Retinal nerve fiber layer measurement by nerve fiber analyzer in normal subjects and patients with glaucoma

A Narrative Review of the Association between Obstructive Sleep Apnea and Glaucoma in Adults

BACKGROUND

Obstructive sleep apnea (OSA) is a sleep disorder, primarily of the upper airway, which not only has a significant impact on quality of life but is also associated with various systemic diseases. Several ophthalmological diseases are also associated with OSA, especially glaucoma. The purpose of this review is to take a closer look at the causality and mutual influence.

METHODS

A systematic literature search was conducted using PubMed. A total of 19 studies with 316,178 adult participants were included.

RESULTS

Eleven of the sixteen studies concentrating on the prevalence of glaucoma in patients with OSA showed an association of both entities. One paper found a higher risk for progression of glaucoma in OSA patients. Five of the sixteen included studies failed to show a correlation between OSA and glaucoma. One study out of three surveying specific ophthalmological parameters showed an influence of OSA therapy on retinal nerve fiber layer (RNFL) thinning and vision. One study showed a rise in intraocular pressure (IOP), while two other studies showed no increase under continuous positive airway pressure (CPAP).

CONCLUSIONS

Our findings suggest an association between OSA and glaucoma and, especially, between OSA and thinning of RNFL. CPAP therapy appears to be also suitable for patients with comorbid glaucoma.

Retinal abnormalities, although relatively common in sleep clinic patients referred for polysomnography, are largely unrelated to sleep-disordered breathing

Study objectives.

There has been long-standing interest in potential links between obstructive sleep apnea (OSA) and eye disease. This study used retinal photography to identify undiagnosed retinal abnormalities in a cohort of sleep clinic patients referred for polysomnography (PSG) and then determined associations with PSG-quantified sleep-disordered breathing (SDB) severity.

Methods

Retinal photographs (n = 396 patients) were taken of each eye prior to polysomnography and graded according to validated, standardized, grading scales. SDB was quantified via in-laboratory polysomnography (PSG; n = 385) using standard metrics. A questionnaire (n = 259) documented patient-identified pre-existing eye disease. Within-group prevalence rates were calculated on a per patient basis. Data were analyzed using multivariate logistic regression models to determine independent predictors for retinal abnormalities. P < 0.05 was considered significant.

Results

Main findings were (1) 76% of patients reported no pre-existing “eye problems”; (2) however, 93% of patients had at least one undiagnosed retinal photograph-identified abnormality; (3) most common abnormalities were drusen (72%) and peripapillary atrophy (PPA; 47%); (4) age was the most common risk factor; (5) diabetes history was an expected risk factor for retinopathy; (6) patients with very severe levels of SDB (apnea hypopnea index ≥ 50 events/h) were nearly three times more likely to have PPA.

Conclusion

Retinal photography in sleep clinic settings will likely detect a range of undiagnosed retinal abnormalities, most related to patient demographics and comorbidities and, except for PPA, not associated with SDB. PPA may be indicative of glaucoma, and any association with severe SDB should be confirmed in larger prospective studies.

Changes of Peripapillary Retinal Nerve Fiber Layer in Childhood Glaucoma: A Systematic Review and Meta-Analysis

Objectives: Retinal nerve fiber layer (RNFL) thickness has been detected by numerous studies about alterations and abnormalities in childhood glaucoma, but these studies have yielded inconsistent results about the RNFL thinning region. The investigation of characteristics of RNFL in pediatric patients would contribute to the deep understanding of the neuropathic mechanisms of childhood glaucoma. Thus, the degree of thinning in different quadrants deserves further discussion and exploration. Method: A systematic literature search was conducted using the Cochrane Central Register of Controlled Trials, Medline, Embase, and PubMed databases to identify clinical studies published from inception to April 1, 2021. Results: Ten studies were included in this review with a total of 311 children with glaucoma and 444 in nonglaucomatous controls. The results revealed that average peripapillary RNFL (pRNFL) thickness was attenuated in pediatric patients with glaucoma [weighted mean difference (WMD) = -20.75; 95% CI -27.49 to -14.01; p < 0.00001]. Additionally, pRNFL thickness in eight quadrants (superior, inferior, temporal, nasal, superotemporal, inferotemporal, superonasal, and inferonasal) had different levels of reduction in the pediatric group of glaucoma. Conclusion: This study indicates that eight regions of RNFL thickness show various degrees of thinning in childhood glaucoma. However, caution is required in the interpretation of results due to marked heterogeneity. Future studies, especially larger samples and multicenter, need to confirm our results.

Cup‐to‐disc ratios of Aboriginal and non‐Aboriginal youths

BACKGROUND

The determination of the cup-to-disc ratio (C/D) is a standard procedure in an eye examination and is pivotal in the diagnosis of glaucoma. Determining the size of the C/D ratios of different races of young people may be helpful in determining the genetically predetermined differences between Aboriginal and non-Aboriginal people. The aim of this study was to determine whether there is a statistically significant difference in the average C/D ratios of young Aboriginal and non-Aboriginal people.

METHODS

The overall average C/D ratios of 104 subjects aged between five and 23 years were compared for two age-matched groups by stereoscopic indirect ophthalmoscopy. Differences between the overall average C/D ratios of the two groups were assessed for significance using an unpaired Student's t test.

RESULTS

While the range of C/D ratios within each group was the same (zero to 0.7), there was a statistical difference (p < 0.001) between the overall average C/D ratios of the Aboriginal (C/D = 0.295) and non-Aboriginal (C/D = 0.159) groups.

CONCLUSIONS

Results indicating a difference between the overall average C/D ratios between Aboriginal and non-Aboriginal young people may have implications for initial assessments of glaucoma in patients of any age.

Scanning Laser Polarimetry and Retinal Thickness Analysis before and after Laser in Situ Keratomileusis

Purpose

To evaluate changes in retinal nerve fiber layer (RNFL) thickness after laserin situ keratomileusis (LASIK) using a scanning laser Polarimeter with fixed corneal compensation (GDx) and the retinal thickness analyzer (RIA).

Methods

Thirty-eight eyes of 19 healthy subjects (10 female and 9 male; mean age 37.0±8.8 years) underwent GDx and RTA measurements before and after LASIK. All subjects revealed mild to high myopia (mean spherical refraction: −4.0±2.75 D). Measurements using GDx were followed by RTA measurements after pupil dilation. All measurements were performed the day before LASIK and 1 week postoperatively.

Results

GDX revealed a decrease in nerve fiber layer thickness measurements after LASIK, but did not reach statistical significance (p>0.05). Using RTA, mean RNFL thickness (MRNFL) and RNFL cross sectional area decreased significantly after LASIK (p=0.03 and p=0.02, respectively).

Conclusions

Scanning laser polarimetry revealed a slight decrease in RNFL thickness measurements after LASIK. MRNFL and RNFL cross section were significantly lower after LASIK using RTA. The changes might be artifacts in a small group of myopic subjects.

Peripapillary retina nerve fiber layer thickness and macular ganglion cell layer thickness in patients with obstructive sleep apnea syndrome

PurposeTo investigate the association of the severity of obstructive sleep apnea syndrome (OSAS) with peripapillary retinal nerve fiber layer (RNFL) and macular ganglion cell-inner plexiform layer (GC-IPL).Materials and methodsIn this cross-sectional study, 145 patients with OSAS and 40 healthy subjects were enrolled. OSAS patients were further divided into mild (n=50), moderate (n=36), and severe (n=59) OSAS groups according to their apnea-hypopnea index (AHI) values. Spectral-domain optical coherence tomography was used to measure the peripapillary RNFL and GC-IPL thicknesses.ResultsThere was no statistical difference between the RNFL thickness in OSAS and control groups (P>0.05). Both average GC-IPL and minimum GC-IPL thicknesses were significantly lower in severe OSAS group than in healthy controls (P<0.05 for both). There was a significant negative correlation between AHI and both average GC-IPL (r=-0.232, P=0.005) and minimum GC-IPL (r=-0.233, P=0.005) thicknesses.ConclusionsOur study results suggest that although RNFL thickness did not differ significantly between OSAS and control groups, ganglion cell layer thickness in OSAS patients is much lower than in healthy population. Ganglion cell thickness showed a significant correlation with the severity of OSAS.

Patterns of Retinal Nerve Fiber Layer Loss in Different Subtypes of Open Angle Glaucoma Using Spectral Domain Optical Coherence Tomography

PURPOSE OF THE STUDY

The purpose of the study was to determine whether there are different patterns of retinal nerve fiber layer (RNFL) thinning as measured by spectral domain optical coherence tomography (SD-OCT) for 4 subtypes of open angle glaucoma (OAG): primary OAG (POAG), normal tension glaucoma (NTG), pseudoexfoliation glaucoma (PXG), and pigmentary glaucoma (PDG) and to compare them with normal controls.

MATERIALS AND METHODS

SD-OCT RNFL thickness values were measured for 4 quadrants and for 4 sectors (ie, superior-nasal, superior-temporal, inferior-nasal, and inferior-temporal). Differences in RNFL thickness values between groups were analyzed using analysis of variance. Paired t tests were used for quadrant comparisons.

RESULTS

Two hundred eighty-five participants (102 POAG patients, 33 with NTG, 48 with PXG, 13 with PDG, and 89 normal patients) were included in this study. All 4 subtypes of OAG showed significant RNFL thinning in the superior, inferior, and nasal quadrants as well as the superior-temporal and inferior-temporal sectors (all P-values <0.0001) compared with normals. POAG and NTG patients had greater RNFL thinning inferiorly and inferior-temporally than superiorly (P-values: 0.002 to 0.018 and 0.006, respectively) compared with PXG patients. In contrast, PDG patients had greater RNFL thinning superiorly and superior-nasally than inferiorly compared with other OAG subtypes (ie, POAG, NTG, PXG groups, with P-values: 0.009, 0.003, 0.009, respectively). Of the 4 OAG subtypes, PXG patients exhibited the greatest degree of inter-eye RNFL asymmetry.

CONCLUSIONS

This study suggests that SD-OCT may be able to detect significant differences in patterns of RNFL thinning for different subtypes of OAG.

Thickness alterations of retinal nerve fiber layer in children with sleep-disordered breathing due to adenotonsillar hypertrophy

OBJECTIVE

This study is designed to assess whether hypoxia which is caused by apnea and hypopnea episodes, has an effect on retinal nerve fiber layer (RNFL) thickness, using optical coherence tomography (OCT) in pediatric patients with Adenotonsillar hypertrophy (ATH).

METHODS

Fifty-seven children patient with AHT, and 31 healthy non-AHT children (between 6 and 12 ages) were enrolled in this study. Obstructive symptoms of the patients with ATH were assessed by using OSA-18 survey. The patients were divided into 2 groups as mild (>60 and <80) and severe (>80) OSAS patients, according to OSA-18 survey total scores. RNFL thickness, in the four quadrants (superior, nasal, inferior and temporal) patient's both eyes, was measured by optical coherence tomography. RNFL parameters of control and patient groups were compared. Correlation between OSA survey scores and RNFL thickness of the patient groups were examined.

RESULTS

A positive correlation was found between ages and RNLF thickness of all subjects enrolled in this study (r=+0.107, p<0.05). And also a poor correlation was found between OSA-18 survey scores and RNFL parameters in patient group (between -0.031 and +0.016 at right and left eyes, p>0.05). No statistically significant alteration in RNFL thickness was found between the patient and control groups (p>0.05).

CONCLUSION

Age range (6-12) of the patients with ATH in our study considers that possible OSAS time was not long enough to affect RNLF thickness. Remembering the risk of optic injury development in children with ATH (in a long term), tonsillectomy and/or adenoidectomy operations shouldn't be delayed.

Relationships among serum lipoprotein lipase mass, visceral fat, and retinal nerve fiber layer thickness

PURPOSE

The purpose of the study was to determine whether there were significant correlations among the serum lipoprotein lipase mass, visceral fat, and the retinal nerve fiber layer (RNFL) thickness.

METHODS

We studied 118 consecutive subjects. Optical coherence tomography (OCT) was used to measure the RNFL thickness. The Pearson correlation coefficient was used to determine the relationships among lipoprotein lipase (LPL) mass, visceral fat area by computed tomography, OCT, and other parameters. We performed a multiple regression analysis to identify independent factors for the RNFL sectors that were the most strongly correlated with the LPL mass and visceral fat area.

RESULTS

The LPL mass was significantly correlated with the nasal RNFL thickness in both eyes (right eye: r = 0.24, p = 0.008, left eye: 0.32, 0.0008) and inferior RNFL thickness in the left eye ( r = 0.23, p = 0.01). The visceral fat area was significantly correlated with the nasal RNFL thickness in both eyes (right eye: r = -0.19, p = 0.04, left eye: -0.30, 0.0008) and the inferior RNFL thickness in the left eye ( r = -0.23, p = 0.01). The subcutaneous fat area was not significantly correlated with any OCT parameters. The multiple regression analysis revealed that age, LPL mass, and visceral fat area were independent contributors to the nasal RNFL thickness in the left eye (age, standard regression coefficient = -0.34 , p = 0.0004; LPL mass, 0.26, 2.49, 0.01; visceral fat area, -0.21, 0.03).

CONCLUSION

A reduction of lipoprotein lipase and accumulation of visceral fat might produce retinal neurodegenerative disorders that decrease the RNFL thickness, especially on the nasal side.

Relationship between severity of obstructive sleep apnea syndrome and retinal nerve fiber layer thickness

PURPOSE

To determine whether there is a significant correlation among the peripapillary retinal nerve fiber layer (RNFL) thickness, foveal thickness, total macular volume, and severity of obstructive sleep apnea syndrome.

DESIGN

Prospective study.

METHODS

We studied 124 consecutive subjects who underwent polysomnography. Optical coherence tomography (OCT) was used to measure the peripapillary RNFL, foveal thickness, and total macular volume. The Pearson correlation coefficient was used to determine the relationship between the apnea-hypopnea index and OCT and other parameters. Multiple regression analysis was used to determine the independent factors for the RNFL sectors that were the most strongly correlated with the apnea-hypopnea index.

RESULTS

The apnea-hypopnea index was significantly and negatively correlated (right eye, r = -0.31, P = 0.0004; left eye, r = -0.39, P < 0.0001) with the nasal RNFL thickness (Pearson correlation analysis). The foveal thickness and total macular volume were not correlated. The intraocular pressure, body mass index, plaque score, and incidence of hypertension were negatively correlated, and the lowest oxygen saturation and mean oxygen saturation were positively correlated with the nasal RNFL thickness in the left eye. Multiple regression analysis showed that the apnea-hypopnea index and age were independent contributors to the nasal RNFL thickness in the left eye (apnea-hypopnea index, standard regression coefficient, -0.30, t value, -2.76, P = 0.007; age, -0.24, -2.36, 0.02, respectively). The nasal RNFL thickness in both eyes decreased significantly based on the severity of the obstructive sleep apnea syndrome.

CONCLUSION

Exacerbation of obstructive sleep apnea syndrome may produce unique retinal neurodegenerative disorders that decrease the nasal RNFL thickness.

The evaluation of retinal nerve fiber layer thickness in patients with obstructive sleep apnea syndrome

Aim. To evaluate the retinal nerve fiber layer (RNFL) thickness in patients with obstructive sleep apnea syndrome (OSAS) by optical coherence tomography (OCT). Materials and Method. We studied 43 new diagnosed OSAS patients and 40 healthy volunteers. Patients underwent an overnight sleep study in an effort to diagnose and determine the severity of OSAS. RNFL analyses were performed using Stratus OCT. The average and the four-quadrant RNFL thickness were evaluated. Results. There was no difference between the average and the four-quadrant RNFL thickness in OSAS and control groups. There was no correlation between apnea-hypopnea index and intraocular pressure. Body mass index of patients with moderate and severe OSAS was significantly higher in patients with mild OSAS. Conclusion. Mean RNFL thickness did not differ between the healthy and the OSAS subjects, however, the parameters were more variable, with a larger range in OSAS patients compared to controls.

Assessment of peripapillary retinal nerve fiber layer thickness using scanning laser polarimetry (GDx VCC) in normal Indian children

Purpose:

To obtain reference values of RNFL thickness in normal Indian children and to study the association of RNFL thickness with central corneal thickness(CCT) and axial length(AL).

Materials and Methods:

200 normal Indian children (mean age 8.6 ± 2.9 yrs) were examined on the GDxVCC. The inferior average (IA), superior average (SA), temporal-superior-nasal-inferior-temporal (TSNIT) average and nerve fiber index (NFI) values were recorded and compared between males and females as well as between the different age groups. The association of TSNIT average with AL and CCT was examined.

Results:

Values for the RNFL parameters were-SA: 64.9 ± 9.7, IA: 63.8 ± 8.8, TSNIT average: 53.5 ± 7.7 and NFI 21.5 ± 10.8. Superior, inferior and TSNIT averages did not differ significantly between males and females (P = 0.25, P = 0.19, P = 0.06 respectively; Mann-Whitney U test). No significant differences were found in TSNIT average across age groups. There was a statistically significant positive correlation between CCT and TSNIT average (r = 0.25, r² = 0.06, P < 0.001). The correlation TSNIT average and AL(r = −0.12; r² = 0.01) was not significant (P = 0.2).

Conclusion:

Reference values for RNFL parameters reported for Indian children are similar those reported in adults. There is a small correlation between central corneal thickness and RNFL as reflected in average TSNIT.

The retinal nerve fibre layer thickness in glaucomatous hydrophthalmic eyes assessed by scanning laser polarimetry with variable corneal compensation in comparison with age-matched healthy children

PURPOSE

To compare the thickness of the retinal nerve fibre layer (RNFL) in hydrophthalmic glaucomatous eyes in children with age-matched healthy controls using scanning laser polarimetry with variable corneal compensation (GDxVCC).

METHODS

Twenty hydrophthalmic eyes of 20 patients with the mean age of 10.64 ± 3.02 years being treated for congenital or infantile glaucoma were included in the analysis. Evaluation of RNFL thickness measured by GDxVCC in standard Temporal-Superior-Nasal-Inferior-Temporal (TSNIT) parameters was performed. The results were compared to TSNIT values of an age-matched control group of 120 healthy children published recently as referential values. The correlation between horizontal corneal diameter and RNFL thickness in hydrophthalmic eyes was also investigated.

RESULTS

The mean ± SD values in TSNIT Average, Superior Average, Inferior Average and TSNIT SD in hydrophthalmic eyes were 52.3 ± 11.4, 59.7 ± 17.1, 62.0 ± 15.6 and 20.0 ± 7.8 μm, respectively. All these values were significantly lower compared to referential TSNIT parameters of age-matched healthy eyes (p = 0.021, p = 0.001, p = 0.003 and p = 0.018, respectively). A substantial number of hydrophthalmic eyes laid below the level of 5% probability of normality in respective TSNIT parameters: 30% of the eyes in TSNIT average, 50% of the eyes in superior average, 30% of the eyes in inferior average and 45% of the eyes in TSNIT SD. No significant correlation between enlarged corneal diameter and RNFL thickness was found.

CONCLUSIONS

The mean values of all standard TSNIT parameters assessed using GDxVCC in hydrophthalmic glaucomatous eyes in children were significantly lower in comparison with referential values of healthy age-matched children.

Retinal nerve fiber thickness is reduced in sleep apnea syndrome

OBJECTIVE

To investigate the prevalence of glaucoma, visual field abnormalities, as well as changes in retinal nerve fiber layer in patients with obstructive sleep apnea syndrome (OSAS).

METHODS

In this cross-sectional study, 51 patients with OSAS were included. Based on apnea hypopnea index (AHI), there were 26, 6 and 19 cases of severe (AHI⩾30), moderate (15⩽AHI<30), and mild (5⩽AHI<15) OSAS, respectively. The control group was matched for age, sex and body mass index. Prevalence of glaucoma and ocular hypertension as well as the following values were assessed and compared between two groups: best-corrected visual acuity, intraocular pressure, central corneal thickness (CCT), cup:disk ratio, mean deviation (MD), pattern standard deviation, and retinal nerve fiber layer (RNFL) parameters using glaucoma diagnosis measurement (GDx).

RESULTS

Seven eyes (6.7%) had intraocular pressure (IOP)>21mmHg; of these, four eyes (3.9%) had glaucoma. No significant difference was detected in CCT between the two groups. IOP was significantly higher in the OSAS group before (p<0.001) and after (p<0.001) correcting for CCT. There was a significant difference between groups in MD and most GDx parameters including DISK (temporal-superior-nasal-inferior-temporal) average (p=0.002), superior average (p=0.05) and nerve fiber indicator (NFI) (p=0.03), where those in the patient group showed lower values. There was a significant positive correlation between AHI and both IOP and NFI.

CONCLUSIONS

OSAS patients had a higher prevalence of glaucoma and ocular hypertension. OSAS patients also had higher IOP, worse visual field indices, and lower RNFL parameters compared with the control group.

Do optic discs get "thinner" or "narrower?"

PURPOSE

To survey the literature to determine how the dimensions of the neuroretinal rim are commonly described, and to clarify and standardize the description of changes in the dimensions of the neuroretinal rim in glaucoma.

MATERIALS AND METHODS

Literature review of 275 articles describing the neuroretinal rim in glaucoma and a survey of ophthalmologists describing 2 disc photographs. Frequencies of descriptors of the neuroretinal rim were surveyed, which included "thinning" and "narrowing."

RESULTS

Of the 275 articles, 80 described the neuroretinal rim clinically. Forty-one articles used "thinning" to describe progressive loss of rim tissue in a radial axis, 13 articles used "narrowing" and rest used "width" to describe the characteristics of neuroretinal rim. Of the 295 ophthalmologists, 264 used "thinner," whereas 31 used "narrower" to describe the neuroretinal rim.

CONCLUSIONS

Accurate phenotyping is an essential part of patient care, research, and training. "Thinning" is currently used more commonly than "narrowing" in the literature to describe progressive loss of the neuroretinal rim in a radial axis. It would be appropriate to use "narrowing" for radial loss or decrease in width and "thinning" for decrease in the thickness of the rim.

Thickness of the retinal nerve fibre layer estimated with the scanning laser polarimeter in healthy children

PURPOSE

The scanning laser polarimeter [GDx variable corneal compensation (VCC)] measures the thickness of the retinal nerve fibre layer (RNFL) and has, therefore, a possible potential for the diagnosis and follow-up of glaucoma in children. The aim of the present study is to establish reference values of the RNFL thickness in children.

METHODS

The RNFL thickness was measured with a GDx VCC in 72 children aged 4 to 15 years without ocular diseases. The difference in the temporal-superior-nasal-inferior-temporal (TSNIT) average (TA), superior average (SA), and inferior average (IA) between the boys and the girls was estimated with a t test. A 95% confidence interval (CI) of the TA, SA, and IA was calculated for the whole group and compared with those of 4 previous studies. The reproducibility of the examination was estimated in 10 consecutive children and was expressed as 95% CI of the differences between the repeated measurements.

RESULTS

There were no statistically significant differences in the TA, SA, and IA between the boys and girls. The 95% CI for the TA, SA, and IA was 61.1+/-1.5, 73.5+/-2.3, and 73.5+/-2.0 microm, respectively. These values did not overlap with those reported previously in the adult groups, confirming a statistically significant age-related thinning of the RNFL. The 95% CI of the differences between the repeated measurements was -0.4+/-1.4 microm for TA, -1.5+/-3.6 microm for SA, and 1.6+/-3.9 microm for IA, suggesting that the examination was reproducible.

CONCLUSIONS

The GDx VCC examination is reproducible in children. The present RNFL results should represent useful reference values in the evaluation of pediatric glaucoma.

Measurement of retinal nerve fiber layer thickness in normal and glaucomatous Cocker Spaniels by scanning laser polarimetry

OBJECTIVE

To measure changes in the thickness of the retinal nerve fiber layer in normal and early glaucomatous dogs with scanning laser polarimetry.

ANIMALS STUDIED

A total of 45 eyes, 32 normal and 13 glaucomatous eyes, of American Cocker Spaniels with primary glaucoma were used. All eyes were evaluated through a complete neuro-ophthalmic examination, tonometry, gonioscopy, slit-lamp biomicroscopy, and indirect ophthalmoscopy prior to enucleation.

METHODS

The retinal nerve fiber layer thickness was measured in anesthetized animals with scanning laser polarimetry (Nerve fiber analyzer, GDx; Laser Diagnostic Technologies, LTD, San Diego, CA, USA). Glaucomatous eyes retained some vision at the time of this study.

RESULTS

The mean +/- SD of the retinal nerve fiber layer thickness was 141.69 +/- 18 microm for normal dogs and 105.08 +/- 23.86 microm for visual glaucomatous dogs. The average retinal nerve fiber layer thickness in the superior and inferior retinal quadrants was 148.03 +/- 8.5 and 141.06 +/- 8.73 microm, respectively, for normal dogs, and 106.61 +/- 25.77 and 107.08 +/- 24.99 microm in the superior and inferior retinal quadrants, respectively, for glaucomatous dogs. The superior to nasal retinal nerve fiber layer thickness ratio was 1.45 for normal dogs and 1.26 for visual glaucomatous dogs.

CONCLUSIONS

Using scanning laser polarimetry it was possible to detect changes in retinal nerve fiber layer thickness in glaucomatous dogs at early stages of the disease. Therefore, this instrument has the potential to improve the clinical management of canine glaucoma by detecting progressive changes to the retinal nerve fiber layer.

Nerve fibre layer analysis with GDx with a variable corneal compensator in patients with multiple sclerosis

PURPOSE

To evaluate the ability of GDx with variable corneal compensator (VCC) compared to visual-evoked potentials (VEPs) and standard automated perimetry (SAP) in the detection of early optic nerve damage in patients with multiple sclerosis (MS).

METHODS

46 eyes of 23 MS patients were included. Ten of them had a history of acute retrobulbar optic neuritis. A control group of 20 normal subjects was also included. All subjects underwent a complete ophthalmological examination and testing with SAP, GDx VCC and VEPs.

RESULTS

19 eyes (41.3%) were abnormal with GDx VCC compared to 38 eyes (82.6%) with SAP and 31 (64.4%) with VEPs. In the optic neuritis group, 9 eyes (69.2%) had optic nerve pallor; SAP was abnormal in 8 of these eyes (61.5%) while VEPs and GDx VCC were abnormal in 6 eyes (46.1%). 2/20 eyes (10.0%) in the control group gave a false-positive abnormal result with SAP. GDx VCC and VEP were normal for all the eyes in the control group.

CONCLUSIONS

GDx VCC is less able to detect early defects in MS patients compared to the currently used standard techniques of SAP and VEPs.

Error in refractive correction and its impact on scanning laser polarimetry

PURPOSE

The GDx VCC is a scanning laser polarimeter which measures thickness of the retinal nerve fiber layer (RNFL). A perpendicular incident laser beam in the RNFL is a prerequisite of a correct measurement of the thickness of this layer. An error in refractive correction could cause an obliqueness of the laser beam and consequently a deviation of the RNFL thickness reading. The present study investigated the influence of error in refractive correction on the estimation of the RNFL thickness and the nerve fiber index (NFI).

METHODS

Totally 32 persons were included in this study, 17 without ocular diseases and 15 with glaucoma. The measurement of the RNFL was carried out first routinely with correction of the spherical equivalent refractive error. Then the measurement was repeated 4 times with excessive refractive correction of +1, +2, -1, or -2 D, respectively. The deviation in RNFL thickness and NFI caused by each overcorrection was calculated. An univariate ANOVA analysis was applied to analyze the influence of the error in refractive correction on the result of thickness of RNFL and the NFI.

RESULTS

The error in refractive correction caused a significant deviation in the RNFL thickness reading and the NFI in both the group without ocular diseases and the group with glaucoma. The influence was different between these 2 groups.

CONCLUSION

A careful correction of refractive error is important for glaucoma diagnosis and follow-up with GDx VCC.

Influence of optic disc size on parameters of retinal nerve fiber analysis with laser scanning polarimetry

PURPOSE

The aim of the study was to evaluate the influence of optic disc size on the variables of laser scanning polarimetry (GDx).

PATIENTS AND METHODS

One hundred and nineteen healthy controls and 161 patients with ocular hypertension (OHT) received detailed ophthalmologic investigation with respect to glaucoma including retinal nerve fiber analysis with GDx (Version 3.0.05x1; Laser Diagnostic Technologies Europe). Optic disc size was measured with planimetry using 15 degrees optic disc photographs. With respect to frequency of optic disc size in the normal population patients were divided in quartiles of equal sample size.

RESULTS

The ratio between retinal nerve fiber layer thickness in the superior and inferior areas in relation to the nasal and temporal regions decreases significantly with increasing optic disc size and the difference between the highest and lowest retinal nerve fiber layer thickness decreases significantly with increasing optic disc size. The results of multivariate neural network analysis increased with larger optic disc size in controls as well as in patients with OHT. Linear regression analysis showed an increase of 9 units (the Number) per 1 mm(2) of optic disc size. A Number above 30, which indicates suspected glaucoma, was detected in more than a third of the normal population investigated if the optic disc area was larger than 3.5 mm(2). Overall, patients with OHT had a higher Number than controls (20.5+/-11.5 vs. 18.1+/-10.4; p>0.05), but the difference between the two groups did not reach a significant level.

CONCLUSIONS

Retinal nerve fiber analysis in patients with an optic disc size larger than 3.5 mm(2) should be interpreted carefully; the Number in particular requires corrections for optic disc size.

Age Effect on Retina and Optic Disc Normal Values

PURPOSE

To investigate retinal thickness and optic disc parameters by the Retinal Thickness Analyzer (RTA) glaucoma program in older normal subjects and to determine any age effect.

METHODS

Subjects over 40 years of age without any prior history of eye diseases were recruited. Only subjects completely normal on clinical ophthalmologic examination and on visual field testing by Humphrey Field Analyzer (HFA) using the SITA 24-2 program were included. A total of 74 eyes from 74 subjects with even age distribution over the decades were enrolled and underwent topographic measurements of the posterior pole and of the optic disc by RTA. The 'glaucoma full' program in software version 4.11B was applied.

RESULTS

Mean patient age was 59.9 +/- 10.3 years with a range from 40 to 80 years. The only parameter intraocular pressure (IOP) correlated with was retinal posterior pole asymmetry (r = 0.27, p = 0.02). IOP itself increased significantly with age (r = 0.341, p = 0.003). Mean defect and pattern standard deviation of the HFA did not correlate with any of the retinal or optic disc measurements. Increasing age correlated significantly with some of the morphologic measurements of the RTA: decreasing perifoveal minimum thickness (r = -0.258, p = 0.026), increased cup-to-disc area ratio (r = 0.302, p = 0.016) and increased cup area (r = 0.338 p = 0.007).

CONCLUSIONS

An age effect exists for some of the retina and optic disc measurements obtained by the RTA.

Associations of ambient illumination with mood: contribution of ophthalmic dysfunctions

Evidence suggests that ocular pathology could reduce light-stimulated neuronal signaling to the suprachiasmatic nuclei. This study investigated associations of ambient illumination with moods, while considering the contribution of ophthalmic dysfunctions. Seventy Black (59%) and White (41%) Americans participated in the study. Their average age was 68.27+/-5.97 years; 73% were women. Baseline data included: physical health, mood, and sociodemographics. Ophthalmic factors including visual acuity, visual field defects, intraocular pressure, vertical and horizontal cup-to-disk ratios, and nerve-fiber-layer thickness were assessed at SUNY Downstate's eye clinic. The following week, participants wore the Actiwatch-L at home to monitor ambient illumination and sleep. Cosine analyses were performed on the logarithm of measured illumination, yielding the mesor and acrophase of daily illumination exposure. Sleep was estimated with an automatic scoring algorithm. Of the sample, 25% reported visual impairment and 85% reported good to excellent health; 27% were visually impaired according to American criteria. Partial correlation analyses showed an inverse correlation of daily illumination levels to depressed mood [r(p)=-0.33, P<0.05], when age, sex, ethnicity, income, BMI, diabetes, hypertension, respiratory disease, and habitual sleep duration were controlled. With further control for ophthalmic factors, the magnitude and significance of the correlation diminished [r(p)=-0.26, NS]. Individuals receiving daily illumination later in the day reported more depressed moods [r(p)=0.36, P<0.01]; of note, this correlation was not significant after control for the covariates [r(p)=0.18, NS]. Regression analysis indicated that the ophthalmic factors explained 13% of the variance in depression. Our results show that both the level and timing of ambient illumination are associated with mood. Furthermore, they suggest that visual impairment has a mediating effect on the associations of ambient illumination with depression, supporting the notion that ocular pathology lessens the efficacy of daily illumination in promoting positive moods.

Retinal nerve fibre layer measurements are reduced in patients with obstructive sleep apnoea syndrome

PURPOSE

To determine the retinal nerve fibre layer (RNFL) thickness in patients with obstructive sleep apnoea syndrome (OSAS) in order to investigate the possibility of detecting early signs of glaucoma in this population.

METHODS

A total of 66 consecutive patients admitted for polysomnographic evaluation of suspected OSAS. Patients underwent an overnight sleep study in an effort to diagnose and determine the severity of OSAS. Patients who had the disease were classified as having mild and severe OSAS, while patients who did not have the disease were classified as controls. All patients received physical, neurological, and ophthalmological evaluation including visual acuity, slit-lamp examination, Goldmann applanation tonometry, gonioscopy with a three mirror contact lens, and fundus examination. After these examinations, patients with glaucoma and patients who had ophthalmological and/or systemic disease known to affect RNFL thickness were excluded from the study. The RNFL thickness was assessed with a scanning laser polarimeter (Nerve Fiber Analyzer GDx, Laser Diagnostic Technologies Inc., San Diego, CA, USA).

RESULTS

A total of 34 patients with obstructive sleep apnoea (19 mild, 15 severe) and 20 age-matched controls were included in the study. The thickness of RNFL was reduced in patients with OSAS compared to controls. The decrease in RNFL was found to be correlated with the severity of sleep apnoea (r=0.78, P=0.01).

CONCLUSIONS

The sleep apnoea syndrome is correlated with a proportional decrease in the RNFL. Decreased ocular perfusion related to hypoxia and vasospasm associated with OSAS may cause RNFL thinning, which may precede clinically detectable glaucoma.

Diurnal variation of intraocular pressure and its correlation with retinal nerve fiber analysis in Turkish patients with exfoliation syndrome

PURPOSE

The purpose was to evaluate the diurnal variation (DV) of intraocular pressure (IOP) in patients with exfoliation syndrome (XS), to measure retinal nerve fiber layer (RNFL) thickness by using scanning laser polarimetry, and to compare these measurements with those of normal subjects.

METHODS

Forty-five subjects with XS and 40 healthy, age/sex matched subjects were recruited into the study. A detailed ophthalmologic examination was performed. IOP measurements were obtained at 08:00 am, 12:00 pm, 03:00 pm, and 06:00 pm. The XS group was further divided into DV > or = 5 mmHg and DV < 5 mmHg groups and also according to the existence of IOP fluctuation. The IOP measurements and RNFL thickness measurements were compared between the groups.

RESULTS

The mean IOP value was found to be highest in the morning both in the XS and control groups. IOP showed a gradual decrease from 8.00 am to 6.00 pm in the control group, whereas a second peak at 03:00 pm was observed in the XS group. There was a fluctuation in 53.3% of the XS group, while none of the healthy subjects showed fluctuation. Superior and inferior ratios were statistically lower in XS patients than those in control subjects (p<0.05). Moreover, in patients with XS showing a DV > or = 5 mmHg and/or a fluctuation, the superior ratio, inferior ratio, the number, superior average and superior integral were significantly different (all p values <0.05) from those of control subjects.

CONCLUSIONS

As the XS patients with high diurnal IOP variation and fluctuating pattern of IOP had lower RNFL thickness measurements, it is crucial to follow up these patients by performing scanning laser polarimetry in order to discover any possible glaucomatous damage at an earlier stage than with the use of conventional visual field analysis.

Image analysis of optic nerve disease

Existing methodologies for imaging the optic nerve head surface topography and measuring the retinal nerve fibre layer thickness include confocal scanning laser ophthalmoscopy (Heidelberg retinal tomograph), optical coherence tomography, and scanning laser polarimetry. For cross-sectional screening of patient populations, all three approaches have achieved sensitivities and specificities within the 60-80th percentile in various studies, with occasional specificities greater than 90% in select populations. Nevertheless, these methods are not likely to provide useful assistance for the experienced examiner at their present level of performance. For longitudinal change detection in individual patients, strategies for clinically specific change detection have been rigorously evaluated for confocal scanning laser tomography only. While these initial studies are encouraging, applying these algorithms in larger numbers of patients is now necessary. Future directions for these technologies are likely to include ultra-high resolution optical coherence tomography, the use of neural network/machine learning classifiers to improve clinical decision-making, and the ability to evaluate the susceptibility of individual optic nerve heads to potential damage from a given level of intraocular pressure or systemic blood pressure.

Scanning laser polarimetry in myopic and hyperopic subjects

PURPOSE

To investigate the effect of refraction error and axial length on retinal nerve fiber layer (RNFL) measurements as obtained by scanning laser polarimetry (SLP).

METHODS

Besides ophthalmological standard examination (refractive error, keratometry, visual acuity, slit-lamp examination, applanation tonometry, funduscopy), perimetry, axial length measurement by means of ultrasound, and SLP were performed. Seventy-five myopic eyes (between -0.75 D and -8.5 D), 24 hyperopic eyes (0.75 D-6.5 D) and 40 emmetropic eyes were investigated. SLP parameters were compared in the different groups.

RESULTS

The statistical analysis of the absolute thickness values of SLP revealed highly significant ( P< 0.01) reductions in average thickness, ellipse average, superior average, inferior average, and superior integral in both myopic and hyperopic eyes in comparison with the emmetropic control eyes. The amount of reduction was between 12.9% (inferior average; myopia) and 30.2% (superior integral; hyperopia). There were no significant differences between myopes and hyperopes. A significant linear correlation for many of the SLP parameters with the refractive error (spherical equivalent) but not with axial length was found in both the hyperopic and the myopic group.

CONCLUSIONS

Despite a wide interindividual range, SLP measurement values decrease with increasing myopia and hyperopia. In clinical practice, such reduced RNFL thickness values should be viewed with the necessary caution and additional polarimetric signs for glaucomatous damage should be taken into consideration.

Scanning laser polarimetry in patients with acute angle-closure glaucoma

PURPOSE

To detect differences in retinal nerve fibre layer (RNFL) measurements between patients with acute angle-closure glaucoma (AACG) and normal subjects using scanning laser polarimetry.

METHODS

This was a comparative cross-sectional study, where 32 eyes of 32 patients with AACG and 28 eyes of 28 normal subjects were imaged using scanning laser polarimetry (The Nerve Fibre Analyzer GDx, Laser Diagnostic Technology Inc., San Diego, CA, USA). The average RNFL thickness in four quadrants and various GDx parameters between the two groups were compared using Mann-Whitney tests with Bonferroni correction.

RESULTS

There were no significant differences in RNFL measurements for the average thickness, ellipse average, inferior, superior, nasal, and temporal average values between the AACG eyes and normal eyes. There were significant differences in some GDx parameters, including superior/nasal ratio (P=0.036), superior ratio (P=0.01), the GDx number (P=0.003), inferior ratio (P<0.001), maximum modulation (P<0.001), and ellipse modulation (P<0.001).

CONCLUSIONS

Various GDx parameters exhibit significant changes in patients following short-duration AACG episodes, making GDx RNFL measurements useful for the diagnosis and follow-up of AACG.

Evaluation of neuroprotective qualities of brimonidine during LASIK

PURPOSE

The effects of LASIK-induced increased intraocular pressure on the optic nerve and nerve fiber layer are poorly understood. This study evaluates the effect of LASIK on several optic nerve parameters, both structural (scanning laser polarimetry) and functional (automated perimetry). In addition, the potential neuroprotective effect of perioperative brimonidine is studied.

DESIGN

Randomized self-controlled, masked trial.

PARTICIPANTS

Fifty-one patients scheduled for routine, bilateral, myopic LASIK. Patients served as their own control and received brimonidine in one eye and placebo in their fellow eye.

METHODS

Patients were treated with the VISX Star S3 Excimer Laser. Patients were evaluated preoperatively and at 1 day, 1 month, and 3 months after LASIK. Topical brimonidine or control vehicle was administrated three times daily for 3 days before surgery. In addition, 1 drop of the respective study drug was instilled at the end of the procedure, and the patient continued the study drug three times daily for 3 weeks after surgery in the respective (randomized) eye.

MAIN OUTCOME MEASURES

Visual acuity, nerve fiber layer analysis, automated visual field, contrast sensitivity, color vision, and pupillary function.

RESULTS

Brimonidine did not change the outcome of any of the parameters analyzed in this study. There was not a statistically significant change in any of the visual field parameters (mean elevation or depression, pattern standard deviation, and corrected pattern standard deviation) measured in either the placebo or brimonidine group postoperatively. However, both the placebo and brimonidine group did show a statistically significant change in many of the direct Nerve Fiber Analyzer GDx (NFA GDx) measures. The average thickness, ellipse, and superior average were generally reduced in both groups. There was, however, no statistically significant change after LASIK in either group in indirect NFA GDx parameters such as symmetry, superior ratio, inferior ratio, or superior/nasal ratio. There was no significant change in optic nerve appearance, contrast sensitivity, or color vision between treatment groups before or after LASIK.

CONCLUSIONS

LASIK with or without brimonidine did not affect the structure or function of the parameters of the optic nerve studied. Direct NFA GDx measures were globally reduced after myopic LASIK; however, the ratio measures were generally unaffected. The reduction in direct, retinal nerve fiber layer measures, in the absence of change in ratio measures and other optic nerve parameters and absence of brimonidine effect, suggest an alteration in corneal birefringence after excimer laser ablation.

Retinal nerve fiber loss pattern in high-tension glaucoma by optical coherence tomography

PURPOSE

To identify the pattern of retinal nerve fiber layer thinning in high-tension primary chronic open-angle glaucoma (HT-PCOAG) using optical coherence tomography.

METHODS

Retinal nerve fiber layer thickness was assessed with optical coherence tomography in 68 healthy controls and 68 age- and refractive error-matched patients with HT-PCOAG were recruited. Patients were divided into 3 subgroups according to their visual field mean deviation: early (> -3 dB), moderate (-3 to -7 dB), and moderately advanced (-7 to -15 dB).

RESULTS

Retinal nerve fiber layer thickness values in inferotemporal and superotemporal regions were significantly lower in all groups of glaucomatous eyes than in healthy eyes (P<0.001). Inferotemporal thickness values were significantly lower than the superotemporal thickness values (P<0.001) in the early glaucomatous stage, but not significantly so in moderate and moderately advanced stages.

CONCLUSIONS

Besides a diffuse retinal nerve fiber layer defect, a localized defect may present in the inferotemporal region in early-stage HT-PCOAG. These results also suggest that optical coherence tomography shows promise in providing quantitative data about the location and extent of retinal nerve fiber layer injury in glaucoma, and the findings are consistent with previous knowledge.

Sensitivity and specificity of the GDx: clinical judgment of standard printouts versus the number

PURPOSE

The Number is a standard parameter of the GDx that reportedly distinguishes normal and glaucomatous eyes. The authors evaluated the sensitivity and specificity of the Number and examined whether expert clinical judgment of GDx printouts leads to a better separation.

MATERIALS AND METHODS

Two experienced observers judged 800 GDx scans on 400 randomly presented printouts from 200 glaucoma patients and 200 age-matched normal subjects. The diagnosis was based on the symmetry analysis printout and was per patient rather than per eye. The observers assessed sensitivity for all glaucoma patients together, and separately for mild, moderate, and severe glaucoma. Their specificity was determined in the group of normal subjects. The same procedure was performed for the Number, at various critical values.

RESULTS

Both observers discriminated better than the Number. At a critical value of 23, the specificity of the Number was 81.5%, which matched the lowest specificity of the 2 observers: 82.5% and 92.0% for observers 1 and 2, respectively. At these specificities, the sensitivity of the 2 observers and of the Number were 92.0%, 89.5%, and 85.5%, respectively. The sensitivity increased with the severity of glaucoma. The Kappa values for intraobserver agreement were 0.80 and 1.0.

CONCLUSIONS

The Number yielded acceptable sensitivity and specificity values at a critical value of 23 in this test population. However, the clinical judgments of the printouts by both expert observers resulted in a better separation between normal and glaucomatous eyes, particularly in the group with mild glaucoma.

Effect of individualized compensation for anterior segment birefringence on retinal nerve fiber layer assessments as determined by scanning laser polarimetry

PURPOSE

Scanning laser polarimetry estimates retinal nerve fiber layer (RNFL) thickness through measurement of retardation of a polarized laser light passing through the naturally birefringent RNFL and cornea. The commercial instrument, the GDx Nerve Fiber Analyzer (Laser Diagnostic Technologies, Inc., San Diego, CA), uses an anterior segment compensator of fixed magnitude and slow polarization axis to eliminate the contribution of the cornea to the total signal. Previous studies have shown up to 30% of patients are not adequately compensated by this method. The aim of this study was to determine the effect of individualized anterior segment compensation using a newly designed variable compensator on estimates of retinal nerve fiber layer thickness compared with those as determined with the fixed compensator in the commercial device.

DESIGN

Comparative, observational case series.

PARTICIPANTS

Twenty-eight eyes from 14 normal participants and 24 eyes from 12 patients with bilateral glaucoma.

METHODS

Using information derived from a scan of the macula, a newly designed variable anterior segment compensator for the GDx was set to neutralize anterior segment birefringence. Normal participants and patients with glaucoma underwent RNFL measurements using the standard (fixed) compensator and the variable compensator. The results were compared using Hotelling's generalized means test and Bonferroni's adjustment for multiple comparisons.

MAIN OUTCOME MEASURES

Standard GDx modulation and thickness parameters as determined with the fixed and variable compensators.

RESULTS

All thickness values were statistically significantly lower as determined with the variable compensator, with no discernible differences in any of the modulation parameters.

CONCLUSIONS

Individualized anterior segment compensation lowers the RNFL thickness values as determined by scanning laser polarimetry compared with those determined with the standard fixed compensator. This may narrow the normal range and increase the discriminating ability of scanning laser polarimetry between normal and disease. However, modulation is less affected, and the modulation parameters may thus prove more useful for distinguishing between normal and glaucoma.

GDx in glaucoma

The purpose of this paper is to review the clinical applications of GDx in the diagnosis and follow-up of glaucoma. The limits and potential of GDx technology are discussed.

Quantitative analysis of axonal loss in band atrophy of the optic nerve using scanning laser polarimetry

AIMS

To measure axonal loss in patients with band atrophy from optic chiasm compression using scanning laser polarimetry (GDx, Laser Diagnostic Technologies, Inc, San Diego, CA, USA) and to evaluate the ability of this instrument to identify this pattern of retinal nerve fibre layer (RNFL) loss.

METHODS

19 eyes from 17 consecutive patients with band atrophy of the optic nerve and permanent temporal hemianopia due to chiasmal compression, and 19 eyes from an age and sex matched control group of 17 healthy individuals were prospectively studied. All patients were submitted to an ophthalmic examination including Goldmann perimetry and evaluation of the RNFL using scanning laser polarimetry. Mean RNFL thickness around the optic disc were compared between the two groups. The diagnostic performance of the deviation from normal analysis provided by the GDx software was also assessed.

RESULTS

The peripapillary RNFL thickness (mean (SD)) of eyes with band atrophy was 47.9 (7.63) micro m, 37.1 (8.48) micro m, 57.0 (9.31) micro m, and 37.2 (8.86) micro m in the superior, temporal, inferior, and nasal regions, respectively. The total average was 43.7 (12.0) micro m. In the control group, the corresponding values were 71.1 (12.2) micro m, 40.4 (10.9) micro m, 85.4 (14.0) micro m, and 49.8 (10.1) micro m. The total average measured 67.9 (11.2) micro m. The measurements from eyes with optic atrophy were significantly different from those in the control group in all regions but the temporal. The deviation from normal analysis provided by the GDx software failed to identify the majority of abnormalities in the temporal and nasal regions of patients with band atrophy.

CONCLUSIONS

Scanning laser polarimetry was able to identify axonal loss in the superior, inferior, and nasal regions, but failed to detect it in the temporal region of the optic disc, despite the fact that this area was clearly altered in eyes with band atrophy. This examination also showed poor sensitivity to detect axonal loss in the nasal region when GDx software analysis was used. The results of this study emphasise that RNFL evaluation using scanning laser polarimetry should be interpreted with caution in the study of eye diseases that lead to axonal loss predominantly in the nasal and temporal areas of the optic disc.

Retinal nerve fiber layer measurement of the Hong Kong chinese population by optical coherence tomography

PURPOSE

To obtain retinal nerve fiber layer (RNFL) measurements by optical coherence tomography in a local, normal Hong Kong Chinese population and to identify the correlation of the measurement with age cross-sectionally.

METHODS

A total of 129 normal Hong Kong Chinese volunteers of different age groups were recruited for this study. The RNFL was measured by optical coherence tomography (OCT; OCT 2000; Humphrey Instruments, San Leandro, CA).

RESULTS

Mean +/- SD peripapillary RNFL measurements at the superior, inferior, temporal, and nasal regions were 145 +/- 24, 154 +/- 26, 98 +/- 32, and 87 +/- 16 microm, respectively. There was a highly significant negative correlation in average RNFL measurement with increasing age (3.3 microm per decade, < 0.001). A significant negative correlation with increasing age was also identified in the RNFL measurements in all the regions ( < 0.05) and decreased at similar extent.

CONCLUSION

The RNFL thickness of the Hong Kong Chinese population, as measured by OCT, appeared to decrease over time. The OCT normative values used for determining RNFL measures "outside of normal" should be developed on an age-specific, or at least age-adjusted, basis.

Disc-to-macula distance to disc-diameter ratio for optic disc size estimation

PURPOSE

To investigate the usefulness of the parameter of disc-to-macula distance (DM) to disc-diameter (DD) ratio in estimating optic disc size.

PATIENTS AND METHODS

A total of 88 normal subjects, 18 subjects with physiological macrodiscs, and 16 early glaucomatous patients were recruited for the study. The DM, which is the horizontal distance between the center of the optic disc and the macula, and DD were determined by planimetry.

RESULTS

No significant differences in DM were observed among the three groups ( = 0.12). The DM:DD ratios were significantly lower ( < 0.0001) in subjects with physiological macrodiscs (1.91 +/- 0.07) compared with normal subjects (2.54 +/- 0.13) and glaucomatous patients (2.50 +/- 0.15). No correlation between the DM:DD ratios and refractive error was found ( = 0.10).

CONCLUSIONS

The DM:DD ratio can be taken as a relative size unit for the optic disc. In particular, the ratio may be clinically useful in the identification of macrodiscs.

Scanning laser polarimetric analysis of retinal nerve fiber layer thickness in Turkish patients with glaucoma and ocular hypertension

PURPOSE

To assess the thickness of the retinal nerve fiber layer (RNFL) in patients with different stages of glaucoma, in comparison with ocular hypertensive (OHT) and healthy subjects in a Turkish population.

METHODS

Scanning laser polarimetry was done with a GDx Nerve Fiber Analyzer (NFA, GDx version, 1.0.08) on 270 eyes with glaucoma, 52 OHT eyes, and 81 normal eyes. The eyes were classified as having early (146 eyes), moderate (66 eyes) and severe (58 eyes) glaucoma based on the Humphrey Visual Field indices. We compared 14 NFA parameters by analysis of variance (ANOVA) and Scheffe multiple comparison analysis. Receiver operator characteristic curves (ROC) and Fisher linear discriminant analysis (LDF) were used to measure the sensitivity and specificity of the NFA parameters.

RESULTS

Except for symmetry, all NFA parameters showed significant differences between the groups (p<0.05). The eyes with glaucoma had significantly thinner RNFL than healthy eyes (p<0.01). The RNFL retardation measurements of OHT eyes were lower than controls, but higher than the early glaucoma group. The sensitivity and specificity of the GDx System were 87% and 72.8%, respectively. Applying LDF, the group with the highest sensitivity and specificity (85.9% and 74.1%) was determined as inferior ratio, superior/nasal ratio, superior maximum and the Number.

CONCLUSIONS

Assessment of RNFL thickness with scanning laser polarimetry can distinguish glaucoma, OHT and normal subjects with relatively high sensitivity and specificity.

Differences by quadrant of retinal nerve fiber layer thickness in healthy eyes

PURPOSE

The purpose of this study was to determine the distribution of retinal nerve fiber layer thickness by quadrant in healthy eyes.

PATIENTS AND METHODS

Forty subjects with healthy eyes were included in the study. A complete ophthalmic examination was performed, including determination of visual fields by automated perimetry. The subjects had no family history of retinal disease or glaucoma. Forty right eyes and 40 left eyes were measured. Retinal nerve fiber layer thickness was measured using simultaneous stereophotographs with stereophotogrammetry at the disc margin. For the total disc and four quadrants, absolute retinal nerve fiber layer thickness and optic disc area was determined using a magnification correction formula.

RESULTS

Comparison of the quadrants showed that the retinal nerve fiber layer thicknesses of the superior, inferior, and nasal quadrants were significantly thicker than the temporal quadrant (P = 0.00006 for right and left eyes). No significant differences were observed between the superior, inferior, and nasal quadrants in the right eye. In the left eye, the superior retinal nerve fiber layer thickness was significantly greater than the inferior (P = 0.028) and nasal retinal nerve fiber layer thicknesses (P = 0.00006), while the inferior was not significantly different from the nasal. No significant difference in quadrant retinal nerve fiber layer thickness was noted between eyes.

CONCLUSIONS

Measurements of retinal nerve fiber layer thickness in healthy eyes show the thinnest quadrant to be the temporal, with the other three quadrants having similar thicknesses. This pattern corresponds to the histologic measurements of retinal nerve fiber layer thickness.

Effect of laser in situ keratomileusis on retinal nerve fiber layer thickness measurements by scanning laser polarimetry

PURPOSE

To determine the effect of laser in situ keratomileusis (LASIK) on retinal nerve fiber layer measurements by scanning laser polarimetry in a large clinical trial.

SETTING

Asan Medical Center, University of Ulsan, Department of Ophthalmology, Seoul, Korea.

METHODS

Scanning laser polarimetry measurements were performed in 59 eyes of 59 consecutive patients who had LASIK. The mean retardation values of the whole measurement ellipse and of the superior, inferior, temporal, and nasal sectors of the ellipse before and after LASIK were compared statistically.

RESULTS

The mean spherical equivalent refractive error was -6.10 diopters (D) +/- 2.34 (SD) (range -1.19 to -15.50 D) preoperatively and -0.31 +/- 0.52 D (range +0.68 to -2.13 D) postoperatively. The mean ablation depth was 94.0 +/- 30.49 microm (range 28.0 to 161.1 microm). The mean postoperative retardation values of all the sectors and of the superior, temporal, inferior, and nasal sectors showed reduced nerve fiber layer thickness (P =.000, P =.000, P =.011, P =.000, and P=.002, respectively).

CONCLUSION

Laser in situ keratomileusis affected nerve fiber layer thickness measurements by scanning laser polarimetry. The change in nerve fiber layer thickness was probably due to modification of the corneal architecture. This effect of keratorefractive surgery should be considered when using scanning laser polarimetry as a diagnostic and follow-up tool for glaucoma.

Scanning laser polarimetry in a selected group of patients with glaucoma and normal controls

PURPOSE

To evaluate the ability of scanning laser polarimetry to discriminate between subjects with glaucoma with specific patterns of visual field defect and normal controls.

METHODS

This cross-sectional, prospective study in a glaucoma practice, focused on subjects with glaucoma with predefined types of visual field defect, including advanced (group A, n = 14), localized (group L, n = 46), or mixed (diffuse and localized) defects (group M, n = 22) and normal controls (n = 32). Scanning laser polarimetry was performed in one study eye per subject. Two methods of analysis were used: a subjective analysis, in which examination printouts with the image of the optic disk manually blocked were classified by two observers masked to the diagnosis, and a logistic regression analysis of the retardation parameters included in the printouts.

RESULTS

The observers correctly identified 97% of the controls and 68% of subjects with glaucoma (overall correct classification of 77%), with 93%, 70%, and 47% of patients from groups A, L, and M, respectively, being correctly identified. The best discrimination obtained with the logistic regression correctly identified 69% of controls and 94% of glaucoma subjects (overall correct classification of 87%). The performance was only slightly better for cases from group A compared with L and M.

CONCLUSIONS

Subjective assessment of the scanning laser polarimetry standard printout of single eyes might not be sensitive enough to detect cases of glaucoma with localized or milder mixed types of visual field defect. The discriminating ability of scanning laser polarimetry improves slightly when logistic regression analysis is employed.

The value of polarimetry in the evaluation of the optic nerve in glaucoma

Scanning laser polarimetry (SLP) is a technology used to measure the thickness of the human retinal nerve fiber layer (NFL) in vivo. SLP has been demonstrated to well differentiate between glaucomatous, ocular hypertensive, and normal eyes, despite overlapping data. Recently increased interest is seen in the polarizing properties of the cornea and crystalline lens that may lead to spurious measurements. Although the instruments that use SLP compensate for these anterior segment polarizing properties, recent interest has focused on the extent and effects of incomplete compensation. If well compensated in all, SLP may better separate diseased from normal eyes. Its promising role in the follow-up of glaucoma is still under investigation.

Screening models for glaucoma

For social and economic reasons, glaucoma screening is a useful and necessary task, with possible benefits for individuals and the health care system arising from the early diagnosis and early therapy of patients with glaucoma. Early treatment of patients with glaucoma decreases the probability that those patients will become blind and lowers the direct and indirect costs for patients with glaucoma. Most of the reported studies dealing with glaucoma screening used only one parameter (eg, intraocular pressure) to detect and to discriminate glaucoma patients from healthy subjects. Glaucoma screening devices might be combined to obtain the best specificity and sensitivity. Because the diagnosis of glaucoma is very closely associated with a morphologic change in the optic nerve head, one screening parameter should be the morphology of the papilla. To increase specificity and sensitivity, a combination of morphologic and functional testing might be useful. In this review, we report the context of glaucoma screening in terms of health economics, the testing quality of devices for functional and morphologic screening, and the results of a pilot study.

Nerve fiber analyzer and short-wavelength automated perimetry in glaucoma suspects: a pilot study

PURPOSE

To test the relationship between the results of short-wavelength automatic perimetry (SWAP) and retinal nerve fiber layer (RNFL) measurements with scanning laser polarimetry (Nerve Fiber Analyzer, NFA) in age-matched normal subjects, glaucoma suspects, and early glaucoma patients.

DESIGN

Case-control study.

PARTICIPANTS AND METHODS

Thirty-eight normal subjects, 32 glaucoma suspects, and 14 early glaucoma patients were recruited. All subjects underwent RNFL assessment by NFA, achromatic visual field testing (24-2 threshold), and repeated SWAP (24-2 threshold blue-on-yellow).

MAIN OUTCOME MEASURES

Mean deviation (MD) of visual field testing and RNFL values were obtained.

RESULTS

Glaucoma suspects were divided into two groups according to their SWAP results: high risk (with SWAP abnormalities) and low risk (with normal SWAP result). No statistically significant difference in SWAP MD and RNFL values were observed between normal and low-risk groups (P > 0.05), but these values were found to be significantly lower in high-risk and early glaucoma groups (P < 0.01).

CONCLUSIONS

This study suggests that RNFL examination by NFA may be a useful test for the early detection of glaucomatous damage of glaucoma suspects. It appears to provide agreement with SWAP abnormalities and is more sensitive than conventional standard automated perimetry.

Nerve fibre layer measurement of the Hong Kong Chinese population by scanning laser polarimetry

PURPOSE

To obtain normal retinal nerve fibre layer (RNFL) measurements by scanning laser polarimetry in a local Hong Kong Chinese population and to identify the correlation of the measurements with age.

METHODS

One hundred and fifty-nine normal Hong Kong Chinese volunteers of different ages were recruited for this study. RNFL values were measured using a Nerve Fibre Analyzer GDx (Laser Diagnostic Technologies, CA).

RESULTS

Mean peripapillary RNFL measurements at the superior, inferior, temporal and nasal regions were 95.0 +/- 15.6, 97.0 +/- 16.3, 47.0 +/- 9.0 and 43.9 +/- 15.1 microns respectively (mean +/- SD). There was a highly significant negative correlation in average RNFL values with increasing age (approximately 1.9 microns per decade, p = 0.001). A significant negative correlation with increasing age was also identified in the RNFL values in all four regions and they decreased by similar amounts (p < 0.05). No correlation with age was observed for relative ratio parameters such as superior/nasal ratio, inferior/nasal ratio and max. modulation (p > 0.05).

CONCLUSION

RNFL values of the Hong Kong Chinese population appeared to decrease over time cross-sectionally. Since they decreased by similar amounts at four regions, use of relative ratio parameters for analysis has an advantage over absolute values, as they were not affected by age.