Mehul C. Mehta

Retinal function in birdshot retinochoroidopathy

Abstract The electroretinograms (ERGs) of 15 patients with birdshot retinochoroidopathy varied from supernormal to non‐recordable, depending upon the severity and the stage of the disease. The abnormal ERGs were characterized by a disproportionate decrease of the b‐wave amplitude compared with the a‐wave amplitude, demonstrating the negative (‐) type response. This distinct ERG pattern has not been observed in any other type of uveitis or chorioretinitis, and appears specific to birdshot retinochoroidopathy. ERG findings indicate that in birdshot retinochoroidopathy the neural layers of the retina are more diffusely and severely involved than the receptor‐retinal pigment epithelium‐choroid complex. In the most advanced stage, the patients becomes night blind with a non‐recordable ERG, a situation that is essentially the same as retinitis pigmentosa, except that pigmentation is conspicuously absent in the fundus.

Correlation of electroretinographic and fluorescein angiographic findings in unilateral central retinal vein obstruction

Abstract• Background: In central retinal vein obstruction (CRVO), electroretinogram (ERG) abnormalities and extensive retinal capillary dropout (CD) in the fluorescein angiogram (FA) are good indicators of retinal ischemia. We retrospectively studied patients with unilateral CRVO and compared the ERG and FA results • Methods: Single white flash ERG, photopic ERG, scotopic ERG and flicker ERG were recordered in 30 cases of unilateral CRVO. We analyzed the correlation between the ERG results and the presence/absence of extensive CD • Results: The ERG b/a-wave amplitude ratios, photopic and scotopic b-wave amplitudes, and flicker amplitudes were significantly smaller (P<0.05) in eyes with extensive CD (n=12, 40%), than in eyes without (n=18, 60%). When the photopic or scotopic b-wave amplitudes were normal or supernormal, extensive CD on FA was absent in all eyes. When the b/a-wave ratios were ≥ 1.0 or when the b-wave amplitudes with white flash or flicker amplitudes were normal or supernormal, extensive CD was present in less than 32% of eyes • Conclusion: These results suggest that the ERG results, especially the b/awave amplitude ratio, are significantly correlated with the presence/absence of CD on FA in CRVO.

Stargardt's disease/fundus flavimaculatus: Psychophysical and electrophysiologic results

Retinal functions were analyzed psychophysically and electrophysiologically in 73 patients (146 eyes) with Stargardts disease/fundus flavimaculatus. Patients were classified into types 1, 2, 3, and 4; patients with type 3 were subdivided into 3E and 3L (early and late onset of initial symptoms). Most had visual acuity (VA) of 20/200 or greater at initial testing. VA declined 0.25 octave/year during follow-up (mean, 6.1 years). Four of 16 patients (25%) older than 40 years had VA of 20/200 or less in the stronger eye. Psychophysical tests (flicker profile, central scotoma, dark adaptation) showed variable degrees of abnormalities. Electrophysiological tests showed significant photopic b-wave amplitude decreases, particularly in type 3E (42.2% of normal). The electro-oculogram light peak/dark trough ratio was abnormal in 60 of 132 eyes (45.5%), especially in type 3E (25 of 34 eyes, 73.5%). Visual prognosis and overall visual function varied depending upon disease type, location of retinal lesions, and age of onset. In Type 3E, overall retinal function was poorest and accompanied by the most severe decline of central vision and function in the surrounding macula.

Hydrogel Tissue Adhesive for Sealing Corneal Incisions

The purpose of the study was to assess the efficacy of a newly developed hydrogel tissue adhesive for sealing corneal incisions in ex vivo rabbit eyes. Simple through-and-through central linear corneal incisions measuring 1–5 mm were created in enucleated rabbit eyes. As controls, the leaking pressures were measured immediately after the incisions had been made. Afterwards, the incisions were sealed with hydrogel adhesive in group 1 and with a single 10-0 nylon suture in group 2. The leaking pressure of each incision was measured after the wounds had been sealed in both groups. The leaking pressures of the controls and the sealed incisions were compared for statistical significance using the Wilcoxon signed rank test. The difference between the leaking pressures before and after sealing the incisions in groups 1 and 2 were compared using the Mann-Whitney rank sum test. The leaking pressures were significantly higher after sealing in both groups 1 and 2 compared to the controls for all incision sizes. The differences in the leaking pressures before and after adhesive application were higher than before and after suturing in all incision sizes. The differences were all statistically significant except for the 1-mm incisions. We conclude that the hydrogel glue has the potential to be used for sealing corneal incisions measuring up to 5 mm.

Best's macular dystrophy with a macular hole

Abstract The occurrence of a macular hole with Bests dystrophy is an extremely rare finding with only one reported case in the literature. We wish to report two cases with typical Bests dystrophy in one eye and a macular hole in the contralateral eye. In one case the Pattern Reversal VER (PVER) was also recorded and graphed as an amplitude‐check size function curve. The PVER changes in this case were grossly subnormal in both the eyes, suggesting a significant degree of bilateral macular impairment. This implies that a significant amount of functional impairment occurs at the vitelliform stage itself, though how this stage progresses to a macular hole is unclear.

Open-Sky Vitrectomy for Severe Retinal Detachment Caused by Advanced Retinopathy of Prematurity

During the period 1974 through 1989, open-sky vitrectomy was performed in 524 eyes of 338 infants under the age of 3 years who had extensive retinal detachment caused by severe cicatricial retinopathy of prematurity (ROP). Typical leukocoria was seen in 93.5% of the eyes. The retina was reattached in 205 eyes (39.2%), and useful vision was obtained in 41 to 62% of these cases. Stage 5 ROP is a significant threat to vision, however, with open-sky vitrectomy, certain cases can be salvaged to some degree.

Effect of optical defocus on the steady state pattern reversal visual-evoked response

The effects of optical defocusing with convex lenses on the amplitudes of pattern reversal visual-evoked response (PVER) were investigated. With the large check size and high-contrast pattern, PVER amplitudes showed a linear decrease in response to initial defocusing up to +5 to +6 dptr. As the degree of defocus increased, the PVER amplitude, though irregular, continued to show reliable, definite responses up to +25 dptr. With the intermediate check size and pattern contrast, PVER amplitudes displayed a linear decrease, but unlike the large-check/high-contrast condition, diminished to noise level after a defocus of greater than +4 to +5 dptr. From these results, we speculate that two phases in this function curve derive from the large-check/high-contrast condition: first, the contrast- or contour-dependent phase, and, second, the luminosity/movement-dependent phase.

Correlating Visual Acuity and Electrooculogram Recordings in Best's Disease

The visual function in 54 eyes of 27 patients with Bests disease was analyzed by retrospectively examining the Snellen visual acuities and the electrooculogram (EOG). Visual acuities, generally well maintained in most patients, were 20/40 (0.5) or better in 41 of 54 (75.9%) eyes, and showed no correlation with age. Those in the cicatricial stage had worse visual acuities than those in the previtelliform stage. The EOG was abnormal in 47 eyes (87.0%) with a subnormal light peak/dark trough (Lp/Dt) ratio less than 1.85. Seven eyes (13.0%) with an Lp/Dt ratio 1.85 or higher had significantly smaller Dt values compared with those with a low Lp/Dt ratio. The Lp/Dt ratio did not correlate with patient age or disease stage. No correlation existed between visual acuities and Lp/Dt ratios. The Lp/Dt ratio did not reflect the severity of the macular lesions. The results indicate that not only a low Lp/Dt ratio but also a low dark trough value in cases with a normal Lp/Dt ratio are helpful in diagnosing Bests disease.

Effect of Hemifield Stimulation on Simultaneous Steady-State Pattern Reversal Electroretinogram and Visual Evoked Response

Steady-state pattern reversal electroretinograms (PERG) and pattern reversal visual evoked responses (PVER) were recorded simultaneously in 4 normal subjects using hemifield stimulation of the upper/lower and nasal/temporal conditions with 95 and 60% stimulus contrasts. A square-wave checker-board pattern (check size 40 min of arc) was used. The temporal frequency (reversal rate) was 6 Hz (12 reversals/s). With nasal/temporal hemifield stimulation, neither the PERG nor the PVER amplitudes differed significantly with either stimulus contrast. With the upper/lower hemifield stimulation, PERG amplitudes were not significantly different; PVER showed a significantly larger amplitude for lower than for upper hemifield stimulation with both contrasts (ANOVA test: p = 0.0064, 95% contrast; p = 0.0018, 60% contrast). PVER amplitudes recorded with lower hemifield stimulation were 2.05 and 2.63 times larger than those elicited with upper hemifield stimulation, for the 95 and 60% contrasts, respectively. The difference in response to the upper/lower hemifield stimulation, observed only in PVER, suggests that the lower stimulus field dominancy may be processed in a visual pathway proximal to the retinal level.

Pattern Reversal Visual-evoked Response as a Prognostic Indicator in Macular Gliosis

We recorded the preoperative pattern reversal visual-evoked responses in 16 subjects (16 eyes) with macular gliosis who underwent membrane-peeling operations. A postoperative visual improvement of one octave or more was observed in 11 of 16 eyes (68.8%). Preoperatively, ten eyes had peak amplitudes greater than or equal to 2 microV, all 11 eyes had either lowpass or bandpass curve shapes, and ten eyes had recordable responses to 20- or 10-minutes of an arc check sizes. Each of the three preoperative criteria was significantly associated with a postoperative visual improvement of one octave or more (P = .01, .02, and .02, respectively). These results demonstrate that the preoperative pattern reversal visual-evoked response can objectively assess the function of the underlying macula in patients with macular gliosis and, consequently, is helpful in determining which patient would most likely benefit from a membrane-peeling operation.