Comparisons of methods to detect glaucomatous optic nerve damage

Discovery and clinical translation of novel glaucoma biomarkers

Glaucoma and other optic neuropathies are characterized by progressive dysfunction and loss of retinal ganglion cells and their axons. Given the high prevalence of glaucoma-related blindness and the availability of treatment options, improving the diagnosis and precise monitoring of progression in these conditions is paramount. Here we review recent progress in the development of novel biomarkers for glaucoma in the context of disease pathophysiology and we propose future steps for the field, including integration of exploratory biomarker outcomes into prospective therapeutic trials. We anticipate that, when validated, some of the novel glaucoma biomarkers discussed here will prove useful for clinical diagnosis and prediction of progression, as well as monitoring of clinical responses to standard and investigational therapies.

Optic Disc Measurements with the 78 Diopter Lens, Zeiss 4-Mirror Contact Lens and Computerized Image Analysing System

We evaluated the 78 diopter (D) lens and Zeiss 4-mirror lens for the measurement of vertical and horizontal optic disc diameters during slit-lamp biomicroscopy and compared the results with the measurements made with the computerized image analysing system (IMAGEnet 640, Topcon, Japan) in 30 eyes of 30 patients. The 78D lens and Zeiss 4-mirror lens measurements both correlated well with the computerized image analysis measurements (r=0.881 for vertical and r=0.895 for horizontal disc diameter measurements with the 78D lens and r=0.883 for vertical and r=0.891 for horizontal disc diameter measurements with the Zeiss 4-mirror lens). The 78D lens measurements overestimated vertical disc diameter by 5.3% and horizontal disc diameter by 4.4%. The Zeiss 4-mirror lens underestimated the vertical disc diameter by 2.4% and horizontal disc diameter by 2.2%. Thus either lens can be used for a quick estimation of the optic disc size, since the results correlate well with the computerized image analysis measurements.

Diagnostic Accuracy of Nonmydriatic Fundus Photography for the Detection of Glaucoma in Diabetic Patients

Purpose. To determine the diagnostic accuracy for glaucoma of a set of criteria with nonmydriatic monoscopic fundus photography (NMFP) in diabetics. Methods. Diabetics recruited from a screening program for diabetic retinopathy and diabetic glaucoma patients recruited from our glaucoma unit were included. Any patient with evidence of diabetic retinopathy was excluded. Diabetic patients had to have no visual field defects to be included as controls. Glaucoma patients had to have a glaucomatous field defect in at least one eye to be included. One NMFP was taken per eye for all subjects. These photographs were evaluated by two masked glaucoma specialists for the presence of the following: bilateral cup to disc (C/D) ratio ≥0.6, notching or thinning of the neuroretinal rim, disc hemorrhages, and asymmetry in the C/D ratio between both eyes ≥0.2. This evaluation led to a dichotomous classification: if any of the above criteria was present, the patient was classified as glaucoma. If none were present, the patient was classified as normal. Results. 72 control subjects and 72 glaucoma patients were included. Evaluation of NMFP had a sensitivity of 79.17% and a specificity of 80.56% for specialist 1 and a sensitivity of 72.22% and a specificity of 88.88% for specialist 2 for the detection of glaucoma. The overall accuracy was 79.83% and 80.55%, respectively. Discussion. NMFP evaluation by a glaucoma specialist may be useful for the detection of glaucoma in diabetics.

Correlation between Optic Nerve Parameters Obtained Using 3D Nonmydriatic Retinal Camera and Optical Coherence Tomography: Interobserver Agreement on the Disc Damage Likelihood Scale

Purpose. To compare stereometric parameters obtained by three-dimensional (3D) optic disc photography and optical coherence tomography (OCT) and assess interobserver agreement on the disc damage likelihood scale (DDLS). Methods. This retrospective study included 190 eyes from 190 patients classified as normal, glaucoma suspect, or glaucomatous. Residents at different levels of training completed the DDLS for each patient before and after attending a training module. 3D optic disc photography and OCT were performed on each eye, and correlations between the DDLS and various parameters obtained by each device were calculated. Results. We found moderate agreement (weighted kappa value, 0.59 ± 0.03) between DDLS scores obtained by 3D optic disc photography and the glaucoma specialist. The weighted kappa values for agreement and interobserver concordance increased among residents after the training module. Interobserver concordance was the poorest at DDLS stages 5 and 6. The DDLS scored by the glaucoma specialist had the highest predictability value (0.941). Conclusions. The DDLS obtained by 3D optic disc photography is a useful diagnostic tool for glaucoma. A supervised teaching program increased trainee interobserver agreement on the DDLS. DDLS stages 5 and 6 showed the poorest interobserver agreement, suggesting that caution is required when recording these stages.

Assessment of optic disc parameters among healthy adult Malays by Heidelberg Retinal Tomograph II

BACKGROUND

This study aims to assess the optic disc characteristics in healthy adult Malays and to correlate them with age, gender and refractive errors.

DESIGN

Cross-sectional study.

PARTICIPANTS

A total of 200 voluntary participants (106 women and 94 men) among Malay students aged 20 to 37 years at Health Campus, Universiti Sains Malaysia.

METHODS

The relationship between Heidelberg Retinal Tomograph parameters with age, gender and refractive error were analysed with correlation tests and multiple linear regression analyses.

MAIN OUTCOME MEASURES

  Twelve parameters, that is, disc area, rim area, cup area, cup to disc area, cup volume, rim volume, height variation contour, cup shape measure, mean cup depth, maximum cup depth, mean retinal nerve fibre layer thickness and retinal nerve fibre layer cross-sectional area.

RESULTS

  Disc area, rim area and cup : disc area ratio averaged 2.24 ± 0.52 (mean ± standard deviation), 1.64 ± 0.32 and 0.25 ± 0.12 mm(2) , respectively. Five parameters (disc area, cup area, cup volume, cup : disc area ratio and mean retinal nerve fibre layer thickness) showed statistically significant difference between men and women. Age was negatively and significantly correlated with rim area with coefficient r = -0.21, P = 0.003. All optic disc parameters were significantly correlated (P < 0.05) with disc area, except cup shape measure.

CONCLUSIONS

  One or more of optic disc parameters were affected significantly by age, gender and disc area in healthy adult Malays' eyes. These factors need to be considered during the evaluation of optic disc.

Concordance of flicker comparison versus side-by-side comparison in glaucoma

BACKGROUND

Flicker comparison superimposes baseline photos of the optic nerve head to subsequent photos, alternating them at a high frequency rate to create the perception of motion showing glaucomatous structural changes over time. The primary purpose of this study was to determine the degree of concordance among examiners in judging glaucomatous progression between serial optic nerve head photos using digital image flicker comparison versus the traditional side-by-side photograph comparison method. The secondary purpose was to determine if flicker comparison was quicker than side-by-side comparison.

METHODS

A total of 29 eyes were selected from patient records at Nittany Eye Associates. Fourteen eyes showed various degrees of glaucomatous structural change among photos, while the remaining 15 eyes had no glaucomatous structural change. Three masked optometrists experienced in glaucoma management graded whether the photos represented glaucomatous change or no change when viewing photos randomly assigned to side-by-side or flicker comparison.

RESULTS

Among multiple graders, flicker comparison gave moderate agreement, whereas side-by-side analysis gave fair agreement. The difference in time between the 2 methods was not statistically significant.

CONCLUSIONS

Flicker comparison is a unique, easy to learn, and an accurate way to view serial optic nerve head photographs. More study is needed to determine if flicker comparison is a useful tool in the clinical management of structural glaucoma progression.

Evaluating the optic disc and retinal nerve fiber layer in glaucoma. I: Clinical examination and photographic methods

Glaucoma is a leading cause of blindness worldwide and is characterized in part by specific changes in the optic disc and retinal nerve fiber layer. Currently, subjective clinical examination and fundus photography are the most common ways of detecting structural change in glaucoma and monitoring its progression. In the first part of this two-part article, the authors overview structural changes of the optic disc and retinal nerve fiber layer in glaucoma and describe and evaluate photographic methods for observing these changes. In the second part of this article (this issue), recent developments in computer-based optical imaging techniques that allow objective evaluation of the optic disc and retinal nerve fiber layer are described.

Systems for staging the amount of optic nerve damage in glaucoma: a critical review and new material

The evaluation of the appearance of the optic disk is central to the diagnosis and management of patients with glaucoma. Grouping patients into categories, monitoring change, and quantitating the rate of change all require some type of quantitative staging of the amount of damage. Though the scientific literature regarding the appearance of the optic disk in glaucoma is extensive, there is remarkably little about quantitative staging of the amount of damage. We have identified eight systems, including the cup/disk ratio system of Armaly. Most of the earlier systems suffer from a failure to take into account the importance of the size of the optic disk. Furthermore, only one system includes early amounts of damage. This review is a critical appraisal of the known methods for staging optic disk damage in glaucoma, including the recent Disk Damage Likelihood Scale, which appears to offer substantial advantages over the other systems.

Managing 'suspicious glaucomatous discs' identified during digital-photography-based diabetic retinopathy screening

PURPOSE

An audit to demonstrate the outcome of patients identified with suspicious glaucomatous discs within a digital-photography-based diabetic retinopathy screening programme.

METHODS

Primary care based digital photographic screening was performed utilising mydriasis and two-field digital photography for all patients with diabetes. Patients identified with discs suspicious of glaucomatous optic neuropathy (GON) were initially referred to an accredited community-based optometrist for further assessment. Some patients were then referred to secondary care where appropriate.

RESULTS

From 1st April 2002 to 31st March 2003 a total of 3868 patients were screened for diabetic retinopathy. This audit revealed that 55 subjects were identified by retinal screeners as having discs suspicious of glaucoma. A total of 29 were already under glaucoma clinic review. A total of 23/26 remaining were referred for an assessment by an accredited optometrist. Of these 13 were normal, 6 were referred to secondary care and 4 failed to attend. The three remaining were referred directly to secondary care.

CONCLUSIONS

All nine referrals to secondary care were deemed appropriate by a glaucoma specialist. This suggests that the system described does not lead to over-referral of suspicious discs - although the issue of how many glaucomatous discs are missed during screening (false negatives) will only be answered in the longer term.

Wertigkeit der Nervenfaserfotografie in der Glaukomdiagnostik

PURPOSE

Primary open-angle glaucoma is characterized by a loss of retinal nerve fibres. The aim of our present study was to evaluate the diagnostic value of retinal nerve fibre layer (RNFL) photography as a routine examination for the early diagnosis of glaucomatous damage.

METHODS

Between 1991 and 2000 we monitored 96 patients with ocular hypertension in a prospective study. RNFL photography was performed in 91 subjects. These photos were evaluated by two independent observers.

RESULTS

The mean image quality of the photos was mediocre. The correlation coefficient for the intraindividual reproducibility (image quality) was 0.713-0.863 (Kendall's coefficient). For the interindividual reproducibility the correlation coefficient was 0.541-0.581 (Somers' coefficient). Regarding the evaluation "RNFL defect yes/no", the correlations were better but there was a discrepancy between the observers.

CONCLUSION

Quality, reproducibility and prognostic value of RNFL photography were disappointing. Although RNFL photography may be convincing and informative in several situations, it is not efficient as a routine technique for the early diagnosis of RNFL damage in glaucoma patients.

Quantitative Analysis of Retinal Nerve Fiber Layer Thickness of Normal Children and Adolescents

PURPOSE

To determine the normal range of retinal nerve fiber layer (RNFL) thickness of normal children and adolescents by optical coherence tomography (OCT).

METHODS

This study analyzed 144 eyes of 72 normal children and adolescents by OCTIII (Zeiss-Humphrey, San Leandro, CA., USA) and the results were compared with the RNFL thickness of Korean adults.

RESULTS

The mean RNFL thickness of the 72 normal children and adolescents was 105.53 +/- 10.33 microm. The mean values for left and right eyes were 104.28 +/- 7.68 microm and 106.79 +/- 12.98 microm, respectively. There was no significant difference in mean RNFL thickness between the 4 quadrants of the left and right eyes (p=0.926). Additionally, the mean RNFL thickness showed a similar size pattern regardless of age (p=0.99). RNFL thickness was found to be greater in adults than in children or adolescents, although the difference was not statistically significant (p=0.295). Likewise, no significant difference was found with gender (p=0.822) or in the pattern of RNFL thickness of 12 sectors between children and adults (p=0.08).

CONCLUSIONS

This study reports RNFL thickness, as determined by OCT, for normal children and adolescents. We found this measurement method to be suitable for the early diagnosis of glaucoma and to the examination of its progression in these subjects. The findings could be used as clinical parameters for adolescent glaucoma.

The Finnish evidence-based guideline for open-angle glaucoma

In most patients, chronic open-angle glaucoma is a slowly progressive disease. Eyes with very high intraocular pressure (IOP > 30 mmHg) represent an exception to this and should be treated and followed extremely intensively. As lowering IOP is, so far, the only means of treating glaucoma, the majority of research reports deal with the IOP-lowering effect of the treatment. The primary goal of treatment, however, is to prevent glaucomatous damage to the structures and function of the eye. The effectiveness of treatment is monitored with optic disc and retinal nerve fibre layer imaging and with visual field examinations. If the glaucomatous changes are progressing, more effective treatment should be given. In the course of follow-up, it should be noted that the changes in the optic nerve structure and function appear and progress at different time-points with delays of up to several years. The assessment of abnormalities is dependent on the examination method and requires a great deal of experience on the part of the examiner. The important risk factors in glaucoma are elevated IOP (even if IOP is within normal range in half of patients ), age, positive family history, exfoliation, race and myopia.

Comparison of clinical optic disc assessment with tests of early visual field loss

PURPOSE

Clinical optic disc assessment may identify glaucomatous optic neuropathy prior to a patient developing visual field abnormalities on achromatic automated peri-metry (AAP). Tests targeting axons that are selectively damaged or whose redundancy is low, such as short wavelength automated perimetry (SWAP) and frequency doubling perimetry (FDP), may detect visual field loss before it is seen on AAP. This study investigated whether patients in whom characteristic glaucomatous optic disc damage was present without AAP abnormalities had visual field abnormalities with SWAP and FDP.

METHODS

A sample of patients (n = 50) with ocular hypertension (normal AAP) were selected, who had SWAP, FDP and stereofundus photography performed. The photographs were then analysed by two glaucoma subspecialists who were masked to the assessments of the other and to the patients' SWAP and FDP results. A categorization of the optic discs was made as either normal or abnormal and this was compared with their SWAP and FDP findings.

RESULTS

On comparing SWAP and FDP with clinical optic disc assessment as the 'gold standard', the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 33%, 92%, 57% and 81%, respectively, for SWAP and 25%, 89%, 49% and 79%, respectively, for FDP.

CONCLUSION

In glaucoma suspects, the study suggests that SWAP and FDP identify subjects with early glaucomatous optic neuropathy missed by AAP.

Glaucomatous optic disc changes in the contralateral eye of unilateral normal pressure glaucoma patients

OBJECTIVE

To evaluate the optic disc for structural abnormalities in the contralateral eye of unilateral normal pressure glaucoma patients.

DESIGN

Cross-sectional study.

PARTICIPANTS

Fifty-three unilateral normal pressure glaucoma patients.

TESTING

Optic disc imaging with the Heidelberg Retina Tomograph (HRT).

MAIN OUTCOME MEASURES

Optic disc structural parameters.

RESULTS

Of the contralateral (normal visual field) eyes, 79.2% were found to have an abnormal optic disc by HRT analysis. Of the glaucomatous (abnormal visual field) eyes, 94.3% were found to have an abnormal disc. The patterns of disc abnormality were defined as marked or moderate diffuse thinning of the neuroretinal rim (NRR) or broad or narrow focal thinning of the NRR. The most common pattern in the contralateral eyes was moderate diffuse thinning of the NRR (45.2%). The most frequently abnormal segments were the nasal superior (73. 8%) followed by the nasal inferior and the global NRR parameter (both 54.8%).

CONCLUSIONS

A high frequency of NRR thinning was found in the contralateral (normal visual field) eyes of unilateral normal pressure glaucoma patients by HRT analysis. Knowing whether these abnormalities predict future progression to the development of visual field abnormality must wait until longitudinal studies are completed. If a disc abnormality is shown to predict future field loss, then early identification will allow early treatment.

Identifying early glaucomatous changes. Comparison between expert clinical assessment of optic disc photographs and confocal scanning ophthalmoscopy

OBJECTIVE

To compare the ability of expert clinicians, using qualitative assessment of stereoscopic optic disc photographs, and confocal scanning laser ophthalmoscope imaging to discriminate between healthy persons and patients with early glaucoma.

DESIGN

Comparative instrument validation study.

PARTICIPANTS

Seventy-two healthy persons and 51 patients with early glaucoma (average visual field mean deviation, -3.6 dB). Early glaucoma was defined as a history of ocular hypertension and a reproducible visual field defect scoring 5 or less in the Advanced Glaucoma Intervention Study classification, regardless of optic disc appearance.

INTERVENTION

Stereoscopic optic nerve head (ONH) photography and Heidelberg Retina Tomograph (HRT) imaging, (Heidelberg Engineering GmbH, Dossenheim, Germany).

MAIN OUTCOME MEASURES

Ability of clinical assessment of stereoscopic ONH photographs and analysis of HRT parameters, taking into account the optic disc size, to detect early glaucomatous optic disc changes.

RESULTS

The specificity of the majority opinion of five observers to detect early glaucomatous optic disc changes was 94.4%, with a sensitivity of 70.6%. Using the HRT analysis, the specificity was 95.8% and the sensitivity was 84. 3%.

CONCLUSIONS

Heidelberg Retina Tomograph image analysis that takes into account the optic disc size is more sensitive than clinical assessment of stereoscopic optic disc photographs in distinguishing between healthy persons and patients with early glaucoma.

Optic nerve evaluation among optometrists

PURPOSE

To determine agreement among optometrists regarding assessment of optic nerve C/D ratios and perceived glaucomatous damage and to separately analyze these results on the basis of residency training, practice setting, and glaucoma patient experience.

METHODS

Fifty-six optometrists from various modes of professional practice evaluated 33 stereoscopic optic nerve photographs. Observers were asked to estimate the vertical cup-to-disk (C/D) ratio and determine the glaucomatous status of the optic nerve. The mean vertical C/D ratio, percentage perceived as glaucomatous, and levels of interobserver and intraobserver agreement (kappa) are reported.

RESULTS

Estimated C/D ratios differ significantly on the basis of training (p = 0.02) practice setting (p = 0.001), glaucoma patient experience (p = 0.001). Glaucomatous damage interpretation was significantly different (p = 0.006) based upon an optometrist's practice setting. Interobserver agreement regarding C/D ratios is significantly higher among optometrists who have completed a residency (kappaw = 0.59) and practice in clinical settings (optometry school/medical center/hospital) (kappaw = 0.59) compared with non-residency-trained optometrists (kappaw = 0.52) and those practicing in commercial settings (kappaw = 0.54). Interobserver agreement of glaucomatous damage is significantly higher among optometrists who have completed a residency (kappa = 0.50) compared with non-residency-trained optometrists (kappa = 0.42).

CONCLUSIONS

Intraobserver agreement is higher than interobserver agreement among optometrists when C/D ratios are estimated and the glaucomatous status of the optic nerve is assessed. Optic nerve evaluation among optometrists is significantly influenced by residency training, practice setting, and glaucoma patient encounters.

Effect of aging on optic nerve appearance: a longitudinal study

AIM

To determine whether aging causes detectable changes in the appearance of the optic disc.

METHODS

A retrospective longitudinal study was performed with quantitative and qualitative evaluations of digitised stereoscopic optic disc photographs of 224 eyes of 224 subjects. There were three groups: 100 normal subjects from the Framingham Eye Study, 68 glaucomatous patients followed longitudinally, and 56 normal subjects and glaucoma patients who had separate sets of disc photos taken on the same day. A disc was considered qualitatively worse if two of three experienced observers agreed that it was worse. Quantitative progression was defined as a >10% decrease in rim/disc area ratio measured with computer assisted planimetry.

RESULTS

With quantitative evaluation, normal eyes (mean follow up 13 years) and same day eyes displayed no statistically significant difference in change of rim/disc area ratios (p=0.095), nor in the number of discs that progressed-five of 100 (5%) v two of 56 (4%) respectively. Glaucomatous eyes (mean follow up 9 years) showed a quantitative loss of disc rim in 24 of 68 (35%), and differed significantly from the normal eyes both in the change of rim/disc area ratio (p<0.0005) and number of discs that progressed (p<0.0005). With qualitative evaluation, the number of progressive discs in the glaucomatous eyes (31%) differed significantly (p<0. 0005) from the normal eyes (3%) and the same day eyes (0%).

CONCLUSIONS

Over a period of follow up appropriate for long term outcome studies in glaucoma, there was no quantitatively or qualitatively detectable neuroretinal rim loss in normal aging optic nerves with stereoscopic optic disc photographs.

The correlation of the visual field with scanning laser ophthalmoscope measurements in glaucoma

PURPOSE

To assess the relationship between Humphrey visual field data and optic disc topographical data collected by the Heidelberg Retina Tomograph (HRT) scanning laser ophthalmoscope in chronic glaucoma patients.

METHODS

The mean deviation (MD) and corrected pattern standard deviation (CPSD) from Humphrey visual fields of 106 eyes of 106 patients with glaucoma were analysed for correlation with the multiple topographical measures calculated by the HRT.

RESULTS

Significant correlations were found between MD of the visual field and several optic disc measurements. These included neuroretinal rim volume, mean nerve fibre layer thickness and cross-sectional area, and the cup shape measure. CPSD correlated significantly only with mean nerve fibre layer cross-sectional area. This pattern was common to the whole circumference of the disc with the exception of the directly temporal segment.

CONCLUSION

Optic disc topography performed by HRT reflects the optic disc pathology in correlation with perimetry.

Vertical cup/disc ratio in relation to optic disc size: its value in the assessment of the glaucoma suspect

AIMS

The vertical cup/disc ratio (CDR) has long been used in the assessment of the glaucoma suspect, though the wide range of CDR values in the normal population limits its use. Cup size is related physiologically to disc size and pathologically to glaucomatous damage. Disc size can be measured at the slit lamp as the vertical disc diameter (DD). The ability of the CDR, in relation to DD, to identify glaucomatous optic discs was investigated.

METHODS

88 normal, 53 early glaucoma, and 59 ocular hypertensive subjects underwent stereoscopic optic disc photography and clinical biometry. Photographs were analysed in a masked fashion by computer assisted planimetry. The relation between vertical cup diameter and DD was explored by linear regression, and expressed in terms of CDR. The upper limit of normal was defined by the 95% prediction intervals of this regression (method 1) and by the upper 97.5 percentile for CDR (method 2). The sensitivity and specificity of CDR to identify an optic disc as glaucomatous was tested with these disc size dependent and disc size independent cut offs in small, medium, and large discs.

RESULTS

The CDR was related to DD by the equation CDR = (-1.31 + (1.194 x DD))/DD. The sensitivity in small, medium, and large discs was 80%, 60%, and 38% respectively for method 1 and 33%, 67%, and 63% respectively for method 2. Specificity was 98.9% (method 1) and 97.7% (method 2).

CONCLUSIONS

The CDR, relative to disc size, is useful clinically, especially to assist in identifying small glaucomatous discs.

Identification of early glaucoma cases with the scanning laser ophthalmoscope

PURPOSE

This study aimed to define the confocal laser scanning ophthalmoscope (Heidelberg Retina Tomograph [HRT]) parameters that best separate patients with early glaucoma from normal subjects.

STUDY DESIGN

A cross-sectional study.

PARTICIPANTS

A total of 80 normal subjects and 51 patients with early glaucoma participated (average visual field mean deviation = -3.6 dB).

INTERVENTION

Imaging of the optic nerve head with the HRT and analysis using software version 1.11 were performed.

MAIN OUTCOME MEASURES

The relation between neuroretinal rim area and optic disc area, and cup-disc area ratio and optic disc area, was defined by linear regression of data derived from the normal subjects. The normal ranges for these two parameters were defined by the 99% prediction intervals of the linear regression between the parameter and optic disc area, for the whole disc, and for each of the predefined segments. Normal subjects and patients were labeled as abnormal if the parameter for either the whole disc or any of the predefined segments was outside the normal range. The sensitivity and specificity values of the method were calculated.

RESULTS

The highest specificity (96.3%) and sensitivity (84.3%) values to separate normal subjects and those patients with early glaucoma were obtained using the 99% prediction interval from the linear regression between the optic disc area and the log of the neuroretinal rim area. Similar specificity (97.5%) and lower sensitivity (74.5%) values were obtained with the 99% prediction interval derived from regression between the disc area and cup-disc area ratios. Poor separation between groups was obtained with the other parameters.

CONCLUSIONS

The HRT, using the technique of linear regression to account for the relationship between optic disc size and rim area or cup-disc area ratio, provides good separation between control subjects and patients with early glaucoma in this population.

Quantitative evaluation of the optic nerve head in early glaucoma

AIMS

Progressive loss of neuroretinal rim tissue is known to occur early in glaucoma and measurement of the neuroretinal rim area is possible by magnification corrected analysis of optic disc photographs (planimetry). This study was performed to determine whether the facility to distinguish between glaucomatous and normal optic discs could be improved upon by: (a) taking into account the known relation between optic disc size and neuroretinal rim area, and (b) measuring rim area in a number of segments, in order to detect focal changes.

METHODS

Planimetric examination of the optic disc photographs of 88 control subjects and 51 patients with early visual field defects was performed. In the control group, multiple linear regression analysis was performed between neuroretinal rim area and optic disc area, age, sex, eye side, refraction, and keratometry. This was repeated for the whole disc and for each of twelve 30 degree segments. Normal ranges were defined by the 98% prediction intervals of the regression analysis and the sensitivity and specificity for correct identification of optic discs in the two groups determined.

RESULTS

Multiple linear regression demonstrated significant associations between the neuroretinal rim area and optic disc area and age in normal subjects. Sensitivity and specificity for glaucoma diagnosis, using the cut off derived from the 98% prediction intervals, was 37.7% and 98.9% respectively when total neuroretinal rim area alone was considered, and 88.7% and 94.3% respectively when the 30 degree segments were included. The most frequent pattern of neuroretinal rim loss was diffuse, followed by thinning in more than one sector and then by thinning in the inferotemporal sector alone.

CONCLUSIONS

This method of optic disc analysis enables the examiner to identify glaucomatous optic discs at the stage of early perimetric loss with a high degree of precision. Optic disc photography is simple, and fundus cameras are widely available. This method for glaucoma case identification may therefore be suitable for the primary care setting as well as hospital practice.

Microperimetry of localized retinal nerve fiber layer defects

The aim of this study was to determine the sensitivity of retinal areas involved in a localized retinal nerve fiber layer (RNFL) defect and to assess correlations between microperimetry and the standard full threshold central 30 deg visual field test. Twenty-five patients with focal RNFL defects, evaluated by means of Argon-blue scanning laser ophthalmoscopy (SLO), underwent an automated 30 deg central visual field examination and a microperimetry with SLO. Microperimetry was performed according to standard procedures (infrared laser for fundus imaging; HeNe laser for 10 candles/m2 background illumination, fixation aid and generation of stimuli; manual fundus tracking). The size of stimuli was Goldmann III with 0.1 sec duration. In eyes with focal RNFL defects a deep microperimetric scotoma of at least 5 dB was found in 12 cases and a mild scotoma (1-4 dB) in 13 cases. These scotomas were mainly located throughout the whole defect or grouped in the temporal or nasal sides of the defect and were characterized by sharp and well-defined borders. With automated perimetry, a scotoma, defined by a single point depression of at least 10 dB or a depression of at least 5 dB in two or more contiguous points corresponding to the RNFL, defect, was found in only 14 out of 25 eyes with microperimetric defect. Focal RNFL defects correspond to localized areas of depressed retinal sensitivity as evaluated by microperimetry. The close correspondence between structural and microperimetric findings suggests that, in hypertensive eyes also, localized RNFL defects correspond to visual dysfunction possibly associated with substantial atrophy of ganglion cells.

Inter-observer agreement in clinical optic disc measurement using a modified 60 D lens

PURPOSE

To assess the inter-observer agreement of the measurement of optic disc dimensions by two observers using a modified 60 dioptre (D) fundus examination lens.

METHOD

The vertical disc and cup diameters of 29 eyes were measured by two independent observers using a 60 D lens modified by incorporation of a 0.1 millimetre scale graticule. The vertical cup/disc ratio was calculated. Inter-observer agreement was assessed by calculation of the inter-observer differences and by the weighted kappa statistic.

RESULTS

The two observers showed good agreement for the measurement of disc diameter (mean difference -0.04; range -0.04, 0.2) and for cup diameter (mean difference -0.03; range 0.3, 0.2). Closer agreement for the vertical cup/disc ratio was achieved (mean kappa 0.96; 95% confidence limits 0.90, 1.0). The 95% confidence limit for the mean inter-observer difference in cup/disc ratio was 0.11, suggesting that a change of > 0.1 in the assessment of the cup/disc ratio by this technique is significant at the 5% level.

CONCLUSION

High inter-observer agreement of optic disc measurement can be achieved with this technique. The method has the potential to improve the clinical evaluation of the optic disc and the precision and accuracy of the clinical measurement of other fundal structures.

Sensitivity and specificity of optic disc variables and analysis of a new variable (MP/D) for glaucoma diagnosis with the Glaucoma-Scope

AIM

In an attempt to use the quantitative optic disc measurements of the Glaucoma-Scope (OIS Sacramento, CA, USA) to distinguish glaucomatous from normal optic discs, a new variable was investigated, the mean disc corrected for the disc size by dividing by the disc area: MP/D.

METHODS

Glaucoma-Scope disc evaluation was performed on 81 eyes of 51 patients split into the following groups based on Humphrey 24-2 visual field and clinical criteria of glaucoma: chronic glaucoma n = 27 (including only early, n = 17, and low tension glaucoma, n = 10), ocular hypertension n = 24, pseudoglaucomatous large discs, n = 12, and normal eyes, n = 18. Classic optic disc variables (the vertical and horizontal c/d ratios, and the c/d area) were compared with the new MP/D index calculating receiver operating characteristic curves.

RESULTS

The MP/D ratio was able to identify the glaucomatous eyes more easily than other ratios. Areas under the curves were: 0.91 (MP/D); 0.87 (c/d area); 0.85 (c/d vertical); and 0.80 (c/d horizontal). The MP/D index was also correlated with the mean deviation (r = 0.466; p = 0.001).

CONCLUSION

MP/D may prove useful in detecting glaucomatous optic nerve damage and could be an interesting screening tool for primary open angle glaucoma.

Comparison of methods to evaluate the optic nerve head and nerve fiber layer for glaucomatous change

PURPOSE

To compare the rates of optic nerve damage in early human glaucoma as measured by four methods to evaluate change in the optic nerve and nerve fiber layer.

METHODS

Four techniques were used to detect progressive glaucomatous damage in a prospective, longitudinal study: (1) qualitative evaluation of stereoscopic color optic disk photographs, (2) qualitative evaluation of monochromatic nerve fiber layer photographs, (3) manual stereoplanimetric measurements of disk rim area, and (4) computerized measurement of peripapillary nerve fiber layer height. One eye of each patient with glaucoma or ocular hypertension was evaluated at the beginning and end of a follow-up period of not less than one year. The rates of structural change measured by these techniques and the rate of visual field change measured with threshold automated perimetry were determined.

RESULTS

We followed up 193 patients for a mean (+/- S.D.) of 3.3 +/- 1.0 years (range, one to six years). Twenty-nine (15%) of 193 eyes progressed by qualitative optic disk evaluation, 14 (7.2%) of 193 eyes progressed by qualitative nerve fiber layer evaluation, seven (3.6%) of 193 eyes progressed by stereoplanimetry, and 24 (13.2%) of 182 eyes progressed by measurement of nerve fiber layer height. Visual field deterioration was detected in 12 (5.2%) of 193 patients and correlated best with qualitative optic disk and nerve fiber layer evaluations. Evaluation by stereoplanimetry and nerve fiber layer height measurement detected change in eyes with primarily diffuse structural damage, a pattern not well detected by qualitative methods.

CONCLUSION

Both qualitative and quantitative methods of optic disk and nerve fiber layer evaluation contribute to the identification of progressive damage, depending on the stage of disease and the characteristics of optic nerve cupping.

Correlation between the progression of optic disc and visual field changes in glaucoma

Visual field test and optic disc evaluation are the standard examination techniques used to detect the onset and progression of glaucoma. This explorative study was performed to assess the temporal correlation between visual field and optic disc changes in eyes with ocular hypertension and well-established glaucoma. Eighty-six hypertensive and 16 glaucomatous eyes were followed up for a period of up to 9 years (average 4.4 yrs) using kinetic and computerized static perimetry and optic disc manual morphometry. Perimetric changes were based on a series of strict criteria and optic disc changes were based as a reduction in the baseline rim area/disc area ratio (R/D) measurement exceeding the 99% confidence interval for intraobserver reproducibility (7.7%). Optic disc changes were found prior to visual field changes in four hypertensive eyes, whereas visual field changes were found prior to disc changes in six glaucomatous eyes (p = 0.042). The results of our explorative study suggest that quantitative optic disc analysis may be more sensitive than visual field examination in detecting early glaucomatous changes, whereas visual field examination may be more sensitive than quantitative optic disc analysis in detecting glaucomatous progressions in eyes with well established glaucoma.

Morphometric analysis of the optic disc surface. The level of smoothness as a diagnostic parameter for glaucoma

PURPOSE

Since the glaucomatous loss of nerve fibers changes the appearance of the optic disc, we evaluated the morphology of the surface of the optic disc in normal and glaucomatous eyes by using a computerized system to provide the reciprocal position of a large number of points placed on its surface in order to study the clinical significance of differences in the 'smoothness' of optic disc surface.

METHODS

The morphology of the optic disc surface was evaluated by means of simultaneous stereoscopic videographic pictures (IMAGEnet X Rev-3.51b-Topcon Europe, The Netherlands): the reciprocal distribution of a large number of points located on the surface of one eye of 100 subjects randomly chosen (45 normal and 55 glaucoma patients) was studied. In order to define the level of 'smoothness' of the optic disc surface, the differences of the relative position of each surface point were studied by measuring the standard deviation (SD) from the average heights of the points (n. ranging from 623 to 1916 depending on the size of the disc area) that identify the optic disc surface.

RESULTS

The coefficient of variation of the reciprocal location of the points, placed on the optic disc surface at the different measurements performed by a single operator was 10.4%. The differences in Optic Disc Surface Smoothness (ODSS) between glaucoma and normal group were statistically significant (p < 0.0001 using Mann-Whitney U test). No correlation was detectable between age and standard deviation. The best threshold value, calculated using ROC methodology, able to separate the two groups was: normal group: SD < or = 17.79 (-1 x 10(-2) mm); glaucoma group: SD > -17.79 (-1 x 10(-2) mm). Such threshold value had a sensitivity of 82.1%, a specificity of 92.2% and a diagnostic precision (DP) of 86.5% in dividing the glaucoma group from the normal group.

CONCLUSION

ODSS is a global index of optic disc conditions based on quantitative measurements of the morphology of the optic disc surface. As such it does not provide information about the location and the characteristics of optic disc damage. Nevertheless, ODSS measurement is able to separate normal from glaucomatous optic disc with a rather interesting sensitivity, specificity and diagnostic precision (DP). As such it could be useful both for research and clinical applications.

Association between quantitative nerve fiber layer measurement and visual field loss in glaucoma

PURPOSE

To evaluate the association between quantitative nerve fiber layer measurements and visual field loss in patients with primary open-angle glaucoma.

METHODS

Quantitative retinal nerve fiber layer measurements were obtained in 53 patients with primary open-angle glaucoma by using confocal scanning laser ophthalmoscopy (cross-section area) and confocal scanning laser polarimetry (retardation ratio). For each eye, three images were obtained with each instrument. An image that was the mean of those three was created and used in all analyses. We investigated the association between global, regional, and hemifield differences in retinal nerve fiber layer measurements and visual field loss with linear regression techniques.

RESULTS

The retardation ratio decreased with increasing mean visual field loss, measured both globally and regionally; R2 (the amount of variation explained by the model) ranged from 8% to 21%. Retinal nerve fiber layer cross-section area was not significantly associated with global measures of visual field loss. The inferior visual field mean deviation increased with decreasing superior retinal nerve fiber layer cross-section area (R2 = 8.2%, P = .04); superior visual field mean deviation was not associated with inferior retinal nerve fiber layer cross-section area (R2 = 2.6%, P = .25). Hemifield differences in visual field mean deviation increased with increasing hemifield differences in retinal nerve fiber layer cross-section area (R2 = 20.0%, P < .001), but not with retardation ratio (R2 = 0.9%, P = .48).

CONCLUSIONS

Quantitative measures of the retinal nerve fiber layer using both confocal scanning laser ophthalmoscopy and confocal scanning laser polarimetry were correlated with visual field loss in glaucoma patients.

Comparison of clinician judgment with digitized image analysis in the detection of induced optic disk change in monkey eyes

PURPOSE

To compare the ability of clinicians to detect change in the photographic appearance of the optic disk with the performance of a system for digitized image analysis.

METHODS

In 11 monkey eyes, a Topcon Imagenet System was used to acquire eight digitized image pairs and four stereoscopic photographs at an intraocular pressure of 10 mm Hg, and then, again, 45 minutes after intraocular pressure was increased to 45 mm Hg. We recently reported detection of global (ten of 11 eyes) and regional (11 of 11 eyes) change in the digitized images of these eyes by using two new statistical strategies for optic disk analysis. For the current study, we evaluated the ability of three clinicians (the authors) to detect a change within the stereoscopic photographs of these 11 optic disks. For each eye, the eight stereoscopic photographs (four at intraocular pressure of 10 mm Hg and four at intraocular pressure of 45 mm Hg) were developed as stereoscopic slides and arranged into four pairs (10/10, 45/45, 10/45, and 45/10 mm Hg). Thus, two pairs represented no change in intraocular pressure (10/10 and 45/45 mm Hg) and the other two pairs represented either an increase or a decrease in intraocular pressure (10/45 and 45/10 mm Hg). The 44 pairs of stereoscopic slides (four pairs for each of 11 eyes) were masked then randomly mixed. On two separate occasions, each clinician evaluated each pair of stereoscopic slides for the presence of absence of optic disk change.

RESULTS

Reproducibility between the two readings of each clinician ranged from .50 to .64 (kappa statistic). Clinicians correctly detected change (as detected by image analysis) within 45% to 64% of the 10/45 and 45/10 pairs of stereoscopic slides. Clinicians correctly indentified no change within 86% to 100% of the 10/10- and 45/45-mm Hg pairs of stereoscopic slides. Clinicians correctly identified no change significantly more often than change (P < .01, chi 2 test). Change was not detected consistently by all three clinicians in any of the 11 eyes.

CONCLUSION

In a controlled experimental setting, digitized image acquisition with extensive secondary statistical analysis more sensitively detected small short-term changes in the surface of the optic disks of monkeys than did three masked clinicians.