Predicting perimetric defects from en face maps of retinal nerve fibre layer reflectance

PURPOSE

To develop criteria to predict visual hemifields with deep perimetric defects based on retinal nerve fibre layer (RNFL) reflectance, in a transparent process whose components can be assessed by independent laboratories analysing data from their own small groups.

METHODS

The analysis was carried out in four stages, using three independent groups of patients-30, 33 and 62 participants-with glaucoma and age-similar controls. The first stage used Group 1 to develop a criterion for RNFL reflectance images at 24, 36 or 48 μm below the inner limiting membrane (ILM). The second stage evaluated the criterion using Group 2. The third stage developed a second criterion to improve performance for Groups 1 and 2 combined. The fourth stage evaluated the second criterion with Group 3. Confidence intervals for sensitivity and specificity were then computed by combining results from all three groups.

RESULTS

The first criterion identified all hemifields with deep defects and no hemifields from controls, using a within-eye reference for healthy RNFL. For Group 2, specificity remained high but sensitivity was reduced. The second criterion improved sensitivity by using location-specific reference values. For Group 3, sensitivity remained high but reduced specificity was found. Confidence intervals showed substantial overlap for the two criteria.

CONCLUSIONS

We developed two criteria to identify patients with deep perimetric defects with high specificity and sensitivity. Several improvements are warranted: automated identification of the fovea-disc angle and optic disc locations, evaluation of normal variation in patterns of RNFL thickness, improved segmentation of ILM and major vasculature, reduction of within-eye variability in RNFL reflectance of healthy eyes, assessment of effects of image quality, assessment of effects of comorbidity and effectiveness of other devices.

Structure-function assessment in glaucoma based on perimetric sensitivity and en face optical coherence tomography images of retinal nerve fiber bundles

Many studies have assessed structure-function relations in glaucoma, but most without topographical comparison across the central 30°. We present a method for assessing structure-function relations with en face images of retinal nerve fiber layer (RNFL) bundles allowing topographical comparison across much of this retinal area. Forty-four patients with glaucoma (median age 61 years) were recruited and tested with Optical Coherence Tomography (OCT) and perimetry. Six rectangular volume scans were gathered, and then montaged to provide en face views of the RNFL bundles. We calculated the proportion of locations showing a perimetric defect that also showed an en face RNFL defect; and the proportion of locations falling on an RNFL defect that also showed a perimetric defect. A perimetric defect for a location was defined as a total deviation (TD) value equal to or deeper than -4 dB. We found that the median (IQR) number of locations with abnormal RNFL bundle reflectance that also had abnormal TD was 78% (60%) and for locations with abnormal TD that also had abnormal RNFL bundle reflectance was 75% (44%). We demonstrated a potential approach for structure-function assessment in glaucoma by presenting a topographic reflectance map, confirming results of previous studies and including larger retinal regions.

Refractive Errors and Binocular Vision Anomalies among Young University Students

It has been reported that refractive errors (RE) and binocular vision (BV) anomalies are common among university students. In this study we aimed to assess RE and BV status among university students in Saudi Arabia, and its relation to the academic performance. We recruited 109 participants (aged from 18 to 21 years). Visual acuity (VA) and objective refraction were used to assess the refractive status. Cover test, near-point convergence (NPC) and stereopsis tests were used to assess the BV status. Convergence insufficiency symptom survey (CISS) was applied to quantify near-work related symptoms. Mann-Whitney U test (p value was set as p < 0.05) was used to compare VA, CISS, NPC and the academic performance between the groups who had heterophoria versus orthophoria. We found that there was only 38% emmetrope, while the percentage of heterophoria was 45.8%. The academic performance was not statistically different among the two groups, but CISS and stereopsis scores were significantly different (p < 0.03). We concluded that RE and BV anomalies were common among university students in Saudi Arabia, but did not affect the academic performance. More studies are warranted to understand the low scores of CISS and stereoacuity, and their association with RE and BV anomalies.

A Novel Stimulus to Improve Perimetric Sampling within the Macula in Patients with Glaucoma

SIGNIFICANCE

Identifying glaucomatous damage to the macula has become important for diagnosing and managing patients with glaucoma. In this study, we presented an approach that provides better perimetric sampling for the macular region, by testing four locations, with a good structure-function agreement.

PURPOSE

We previously presented a basis for customizing perimetric locations within the macula. In this study, we aimed to improve perimetric sampling within the macula by presenting a stimulus at four locations, with maintaining a good structure-function agreement.

METHODS

We tested one eye each of 30 patients (aged 50 to 88 years). Patients were selected based on observed structural damage to the macula, whereas perimetric defect (using 24-2) did not reflect the locations and extent of this damage. We used en face images to visualize retinal nerve fiber bundle defects. To measure perimetric sensitivities, we used a blob stimulus (standard deviation of 0.25°) at the 10-2 locations. A perimetric defect for a location was defined as any value equal to or deeper than -4, -5, and -6 dB below the mean sensitivity for 37 age-similar controls (aged 47 to 78 years). We also presented an elongated sinusoidal stimulus for 20 patients at four locations within the macula, in which we defined a perimetric defect as any value below the 2.5th percentile from controls.

RESULTS

The -4, -5, and -6 dB criteria identified perimetric defects in 14, 13, and 11 patients, respectively. When testing with the elongated stimulus, 18 patients were identified with perimetric defect. The perimetric defects were consistent with the structural damage.

CONCLUSIONS

The elongated stimulus showed a good structure-function agreement with only four testing locations as compared with 68 locations used with the blob stimulus. This demonstrates a clinical potential for this new stimulus in the next generation of perimetry.

Effects of Cyclopentolate Hydrochloride Dosage on Anterior Segment Parameters in Young Adults (Measured with Pentacam)

Purpose

To assess the effects of 0.5% and 1% cyclopentolate on the main parameters of the anterior segment (central corneal thickness (CCT), anterior chamber angle (ACA), depth (ACD) and volume (ACV)) in low/moderate myopia and hyperopia along with the effect on IOP.

Patients and Methods

Both eyes of 30 subjects (15 myopic and 15 hyperopic) with mean age±standard deviation of 21.4±3.6 years were enrolled. Each participant was administered two drops of cyclopentolate 1% in the right eye and two drops of cyclopentolate 0.5% in the left eye, 15 minutes apart. All participants underwent intraocular pressure (IOP) measurement using noncontact tonometry, and anterior chamber parameter measurement using Pentacam.

Results

Following the use of 0.5% and 1% cyclopentolate among the hyperopic group, there was a statistically significant increase in ACD for 1% (pre 2.762±0.28 mm and post 2.89±0.25 mm) and 0.5% (pre 2.71±0.28 and post 2.86±0.27 mm) and ACV for 1% (pre 141.40±20.59 mm³ and post 154.35±19.69 mm³) and 0.5% (pre 137.40±20.48 mm³ and post 152.93±20.50 mm³). In contrast, ACA decreased with both doses 1% and 0.5%, but was not statistically significant (p for both >0.05%). With 0.5% and 1% cyclopentolate among the myopia group, there was a significant increase in ACD following cyclopentolate 1% (pre 3.18±0.22 mm and post 3.25±0.21 mm) and 0.5% (pre 3.200±0.22 mm and post 3.26±0.05 mm), p˂0.05. The ACV was significantly increased following 1% cyclopentolate, p˂0.001. The ACA showed a statistically significant decrease following cyclopentolate 1%, P=0.01, but not a significant decrease after cyclopentolate 0.5%, P=0.170. There was a significant increase in the IOP after 1%, p˂0.001, while a decrease with 0.5%, p=0.008.

Conclusion

A topical dosage of cyclopentolate 1% showed significant changes in ACA and ACV among the hyperopia and myopic groups compared to 0.5%. Therefore, it is important to consider the use of a 0.5% cyclopentolate dosage to minimize changes to anterior chamber parameters.

Customizing Perimetric Locations Based on En Face Images of Retinal Nerve Fiber Bundles With Glaucomatous Damage

Purpose

Prior studies suggested the use of customized perimetric locations in glaucoma; these studies were limited by imaging only the superficial depths of the retinal nerve fiber layer (RNFL) and by prolonged perimetric testing. We aimed to develop a rapid perimetric test guided by high-resolution images of RNFL bundles.

Methods

We recruited 10 patients with glaucoma, ages 56 to 80 years, median 68 years, and 10 controls, ages 55 to 77 years, median 68 years. The patients were selected based on discrepancies between locations of glaucomatous damage for perimetric and structural measures. Montaging was used to produce optical coherence tomography en face images of the RNFL covering much of the 24-2 grid locations. In experiment 1, we presented the Goldmann size III stimulus at preselected retinal locations of glaucomatous damage, using just two contrasts. In experiment 2, we developed an elongated sinusoidal stimulus, aligned within the defect, to measure contrast sensitivities; abnormalities were defined based on lower 95% reference limits derived from the controls.

Results

The percentage of predicted locations where size III was not seen at 28 dB ranged from 16% to 80%, with a median of 48%. Contrast sensitivity for the sinusoidal stimulus was below the 95% reference range for 37 of 44 stimuli aligned within the defects.

Conclusions

We developed methods for rapid perimetric testing guided by en face images of the RNFL bundles in patients with glaucoma. Results indicated ganglion cell damage under all of the visible RNFL defects.

Translational Relevance

Customized perimetric locations have potential to improve clinical assessment of glaucoma.

A basis for customising perimetric locations within the macula in glaucoma

PURPOSE

It has been recognised that the 24-2 grid used for perimetry may poorly sample the macula, which has been recently identified as a critical region for diagnosing and managing patients with glaucoma. We compared data derived from patients and controls to investigate the efficacy of a basis for customising perimetric locations within the macula, guided by en face images of retinal nerve fibre layer (RNFL) bundles.

METHODS

We used SD-OCT en face montages (www.heidelbergengineering.com) of the RNFL in 10 patients with glaucoma (ages 56-80 years, median 67.5 years) and 30 age-similar controls (ages 47-77, median 58). These patients were selected because of either the absence of perimetric defect while glaucomatous damage to the RNFL bundles was observed, or because of perimetric defect that did not reflect the extent and locations of the glaucomatous damage that appeared in the RNFL images. We used a customised blob stimulus for perimetric testing (a Gaussian blob with 0.25° standard deviation) at 10-2 grid locations, to assess the correspondence between perimetric defects and damaged RNFL bundles observed on en face images and perimetric defects. Data from the age-similar controls were used to compute total deviation (TD) and pattern deviation (PD) values at each location; a perimetric defect for a location was defined as a TD or PD value of -0.5 log unit or deeper. A McNemar's test was used to compare the proportions of locations with perimetric defects that fell outside the damaged RNFL bundles, with and without accounting for displacement of ganglion cell bodies.

RESULTS

All patients but one had perimetric defects that were consistent with the patterns of damaged RNFL bundles observed on the en face images. We found six abnormal perimetric locations of 2040 tested in controls and 132 abnormal perimetric locations of 680 tested in patients. The proportions of abnormal locations that fell outside the damaged RNFL bundles, with and without accounting for displacement of the ganglion cell bodies were 0.08 and 0.07, respectively. The difference between the two proportions did not reach statistical significance (p = 0.5 for a one-tailed test).

CONCLUSIONS

We demonstrated that it is effective to customise perimetric locations within the macula, guided by en face images of the RNFL bundles. The perimetric losses found with a 10-2 grid demonstrated similar patterns as the damaged RNFL bundles observed on the en face images.