Silicone oil insulation effects on flash electroretinogram and visual evoked potential in patients with retinal detachment / Efectos del aislamiento del aceite de silicona sobre el electrorretinograma flash y el potencial evocado visual en pacientes con desprendimiento de retina

Background: Silicone oil is used as endotamponade following vitreoretinal surgery to maintain the retina reattached when indicated. This study investigates the hypothesis that silicone oil causes insulation effects on the retina by affecting its response to light. Methods: Electrophysiological responses to a flash stimulus were recorded using full-field electroretinography (ERG) and visual evoked potentials (VEP). Recordings were performed in 9 patients who underwent surgery for retinal detachment, before (1–2 days) and after (2–3 weeks) silicone oil removal (SOR) in both the study and the control eye. Flash ERG and VEP recordings were performed according to the ISCEV standard protocol. Results: Statistically significant differences were found in the study eye in the amplitudes of the ERG responses and their corresponding ratios, i.e. the amplitude after SOR over the amplitude before SOR, in all conditions tested. No differences were observed in the control eye. The mean ratio of photopic ERG response was 3.4 ± 2.4 for the study and 1.0 ± 0.3 for the control eye (p<0.001). The mean ratio of ERG flicker response was 3.1 ± 2.4 and 1.0 ± 0.3, respectively (p = 0.003). Scotopic flash ERG ratio was 5.0 ± 4.4 for the study and 1.3 ± 0.6 for the control eye (p = 0.012). No differences were observed for the amplitude and latency of flash VEP response after SOR. Conclusions: Silicone oil causes a reduction in flash ERG responses; no effect was found on flash VEP responses. ERGs in eyes filled with silicone oil should not be considered representative of retinal functionality, in contrast to VEPs, which are not affected by silicone oil presence.(AU)

Silicone oil insulation effects on flash electroretinogram and visual evoked potential in patients with retinal detachment.

BACKGROUND: Silicone oil is used as endotamponade following vitreoretinal surgery to maintain the retina reattached when indicated. This study investigates the hypothesis that silicone oil causes insulation effects on the retina by affecting its response to light. METHODS: Electrophysiological responses to a flash stimulus were recorded using full-field electroretinography (ERG) and visual evoked potentials (VEP). Recordings were performed in 9 patients who underwent surgery for retinal detachment, before (1-2 days) and after (2-3 weeks) silicone oil removal (SOR) in both the study and the control eye. Flash ERG and VEP recordings were performed according to the ISCEV standard protocol. RESULTS: Statistically significant differences were found in the study eye in the amplitudes of the ERG responses and their corresponding ratios, i.e. the amplitude after SOR over the amplitude before SOR, in all conditions tested. No differences were observed in the control eye. The mean ratio of photopic ERG response was 3.4 ± 2.4 for the study and 1.0 ± 0.3 for the control eye (p<0.001). The mean ratio of ERG flicker response was 3.1 ± 2.4 and 1.0 ± 0.3, respectively (p = 0.003). Scotopic flash ERG ratio was 5.0 ± 4.4 for the study and 1.3 ± 0.6 for the control eye (p = 0.012). No differences were observed for the amplitude and latency of flash VEP response after SOR. CONCLUSIONS: Silicone oil causes a reduction in flash ERG responses; no effect was found on flash VEP responses. ERGs in eyes filled with silicone oil should not be considered representative of retinal functionality, in contrast to VEPs, which are not affected by silicone oil presence.

Small-aperture monovision and the Pulfrich experience: absence of neural adaptation effects.

PURPOSE: To explore whether adaptation reduces the interocular visual latency differences and the induced Pulfrich effect caused by the anisocoria implicit in small-aperture monovision. METHODS: Anisocoric vision was simulated in two adults by wearing in the non-dominant eye for 7 successive days, while awake, an opaque soft contact lens (CL) with a small, central, circular aperture. This was repeated with aperture diameters of 1.5 and 2.5 mm. Each day, monocular and binocular pattern-reversal Visual Evoked Potentials (VEP) were recorded. Additionally, the Pulfrich effect was measured: the task of the subject was to state whether a a 2-deg spot appeared in front or behind the plane of a central cross when moved left-to-right or right-to-left on a display screen. The retinal illuminance of the dominant eye was varied using neutral density (ND) filters to establish the ND value which eliminated the Pulfrich effect for each lens. All experiments were performed at luminance levels of 5 and 30 cd/m(2). RESULTS: Interocular differences in monocular VEP latency (at 30 cd/m(2)) rose to about 12-15 ms and 20-25 ms when the CL aperture was 2.5 and 1.5 mm, respectively. The effect was more pronounced at 5 cd/m(2) (i.e. with larger natural pupils). A strong Pulfrich effect was observed under all conditions, with the effect being less striking for the 2.5 mm aperture. No neural adaptation appeared to occur: neither the interocular differences in VEP latency nor the ND value required to null the Pulfrich effect reduced over each 7-day period of anisocoric vision. CONCLUSIONS: Small-aperture monovision produced marked interocular differences in visual latency and a Pulfrich experience. These were not reduced by adaptation, perhaps because the natural pupil diameter of the dominant eye was continually changing throughout the day due to varying illumination and other factors, making adaptation difficult.

Xerophthalmia and acquired night blindness in a patient with a history of gastrointestinal neoplasia and normal serum vitamin A levels.

A 69-year-old male patient presented to our department with a 3-month history of nyctalopia. Reviewing of his general health revealed a history of gastrointestinal tumor treated with a modified WHIPPLE operation. Ocular findings at presentation included mild xerophthalmic features and nonspecific pigmentary retinal changes. A standard full-field electroretinogram (ERG) was obtained that showed normal photopic function and extinguished scotopic function. The ocular symptoms, the history and the ERG findings suggested vitamin A deficiency as a possible cause for his complaints. Serum vitamin A levels were subsequently requested, but the results were within normal limits. Despite the normal serum vitamin A levels, the patient was instructed to commence treatment with high doses of oral vitamin A supplements. One month after the onset of the treatment, the patient reported that his visual function has significantly improved, while repeat ERG testing revealed that scotopic function has improved to normal levels. This case highlights that in patients with acquired night blindness due to vitamin A deficiency, the ERG responses possibly represent a more sensitive marker compared to the serum levels of vitamin A.

Contrast sensitivity in the 'good eye' of adult patients with severe impairment in the other eye.

PURPOSE: It is widely accepted that monocular deprivation results in improved visual performance in the non-pathological eye. The current study investigates the effect of deprivation due to severe impairment in one eye during late childhood or adulthood, on the spatial performance of the fellow 'good' eye. METHODS: Twenty patients (age: 29 ± 9 years) with severe visual impairment in one eye (visual acuity equal or worse than count fingers at 1 m), for a period longer than 2 years, participated in the study. Only patients with an age less than 50 years and monocular deprivation onset greater than 9 years were included. On the basis of the time of deprivation the patients were categorised into two subgroups: (i) long-past deprivation (N = 8, age 28 ± 8 years, 9-20 years of deprivation) and recent deprivation (N = 12, age 30 ± 11 years, 2-4 years of deprivation). Eighteen more participants (age: 28 ± 5 years) with normal binocular vision served as the control group. Best-corrected contrast sensitivity was evaluated using reversing (2 Hz) vertical sinusoidal gratings. Seven spatial frequencies (1, 2, 4, 8, 12, 16 and 24 c/deg) were tested. Performance of the control group was tested both monocularly (dominant eye) and binocularly. RESULTS: In normal subjects, binocular viewing improved contrast sensitivity on average by 4.2 dB (corresponding to a 70% improvement in contrast threshold) compared to monocular recordings. Average contrast sensitivity in subjects with impaired vision in one eye was found to be higher by 5.0 dB (corresponding to an 83% improvement in contrast threshold) compared with the dominant eye of the control group. The increase in sensitivity was independent of spatial frequency. No differences were observed between the two subgroups with recent and long-past deprivation. CONCLUSIONS: Notable improvement in contrast sensitivity was found in the non-pathological eye of patients with severe impairment in the other eye at an age after the "critical" period of visual development. These findings are consistent with growing evidence supporting functional changes as a result of altered experience or injury in the adult vision system.

Comparison of visual acuity charts in young adults and patients with diabetic retinopathy.

PURPOSE: To compare visual acuity (VA) assessed in healthy eyes and eyes with diabetic retinopathy (DR) using three different logMAR charts: the Sloan letter European-wide chart, the tumbling E chart, and the Landolt C chart. METHODS: Measurements on one eye of 40 volunteers (aged 29 ± 4 years) without visual impairment and 31 DR patients (aged 70 ± 9 years) with mild/moderate visual impairment were included. Visual acuity was assessed, with habitual refractive correction, using each of the three charts. Bland-Altman charts were constructed, and 95% limits of agreement were calculated to measure agreement. RESULTS: Mean VA in the group of young adults was -0.05 ± 0.10 (Sloan letter), -0.02 ± 0.13 (tumbling E), and 0.00 ± 0.12 (Landolt C) logMAR. Average VA estimates differed to a statistically significant extent between all charts. Mean VA in the DR group was 0.46 ± 0.25 (Sloan letter), 0.48 ± 0.26 (tumbling E), and 0.59 ± 0.28 (Landolt C). A statistically significant difference was observed for average Sloan letter versus Landolt C (p < 0.001) and tumbling E versus Landolt C (p < 0.001) acuities. Moreover, in healthy eyes, a moderate correlation (r = -0.38, p = 0.015) was found between the discrepancy in Sloan letter and Landolt C acuity and the mean VA estimate. The 95% limits of agreement were wide (more than approximately 0.2 logMAR for each comparison) and wider in the DR group chart comparisons than in healthy eyes. CONCLUSIONS: Landolt C charts resulted in worse VA estimates compared with letter and tumbling E charts in both young adults and visually impaired subjects with DR. These differences seem more pronounced in DR patients who exhibit worse VAs. The specific study population must be considered in comparing outcomes from different clinical practices.

Interocular differences in visual latency induced by reduced-aperture monovision.

PURPOSE: To explore the interocular differences in the temporal responses of the eyes induced by the monocular use of small-aperture optics designed to aid presbyopes by increasing their depth-of-focus. METHODS: Monocular and binocular pattern-reversal visual evoked potentials (VEPs) were measured at a mean photopic field luminance of 30 cd/m(2) in seven normal subjects with either natural pupils or when the non-dominant eye wore a small-aperture contact lens (aperture diameter 1.5, 2.5 or 3.5 mm, or an annular opaque stop of inner and outer diameters 1.5 and 4.0 mm respectively). Responses were also measured with varying stimulus luminance (5, 13.9, 27.2 and 45 cd/m(2)) and a fixed 3.0 mm artificial pupil. RESULTS: Mean natural pupil diameters were 4.7 and 4.4 mm under monocular and binocular conditions respectively. The small-aperture contact lenses reduced the amplitude of the P100 component of the VEP and increased its latency. Inter-ocular differences in latency rose to about 20-25 ms when the pupil diameter of the non-dominant eye was reduced to 1.5 mm. The measurements with fixed pupil and varying luminance suggested that the observed effects were explicable in terms of the changes in retinal illuminance produced by the restrictions in pupil area. CONCLUSIONS: The anisocoria induced by small-aperture approaches to aid presbyopes produces marked interocular differences in visual latency. The literature of the Pulfrich effect suggests that such differences can lead to distortions in the perception of relative movement and, in some cases, to possible hazard.

Binocular summation improves performance to defocus-induced blur.

PURPOSE: To assess whether there are any advantages of binocular over monocular vision under blur conditions. METHODS: The effect of defocus, induced by positive lenses, was measured on the pattern reversal visual evoked potential (VEP) and on visual acuity (VA). Monocular (dominant eye) and binocular VEPs were recorded from 13 volunteers (average age, 28 ± 5 years; average spherical equivalent, -0.25 ± 0.73 D) for defocus up to 2.00 D using positive powered lenses. VEPs were elicited using reversing 10 arcmin checks (4 reversals/s). The stimulus subtended a circular field of 7° with 100% contrast and mean luminance 30 cd/m(2). VA was measured under the same conditions using ETDRS charts. All measurements were performed at 1 m viewing distance with best spectacle sphero-cylindrical correction and natural pupils. RESULTS: With binocular stimulation, amplitudes and implicit times of the P100 component of the VEPs were greater and shorter, respectively, in all cases than for monocular stimulation. Mean binocular enhancement ratio in the P100 amplitude was 2.1 in focus, increasing linearly with defocus to be 3.1 at +2.00 D defocus. Mean peak latency was 2.9 ms shorter in focus with binocular than for monocular stimulation, with the difference increasing with defocus to 8.8 ms at +2.00 D. As for the VEP amplitude, VA was always better with binocular than with monocular vision, with the difference being greater for higher retinal blur. CONCLUSIONS: Both subjective and electrophysiological results show that binocular vision ameliorates the effect of defocus. The increased binocular facilitation observed with retinal blur may be due to the activation of a larger population of neurons at close-to-threshold detection under binocular stimulation.

Myopia and visual acuity impairment: a comparative study of Greek and Bulgarian school children.

PURPOSE: To compare the proportions of school children with myopia and impaired visual acuity in Greece and Bulgaria. METHODS: A sample of 898 children, aged 10-15 years, was selected from two primary and two secondary schools in a Greek city (Heraklion), and one primary and secondary school in a Bulgarian city (Stara Zagora). Five hundred and eighty eight children were Greek (65.5%, mean age 12.5 +/- 0.08 years) and 310 Bulgarian (34.5%, age 12.4 +/- 0.07 years). VA was assessed with the habitual refractive correction. Refractive error was measured in the absence of cycloplegia using an auto-refractor. RESULTS: The percentage of children, tested with their habitual refractive correction, with decimal VA <0.5 in at least one eye was 11.7% (95% CI 9.1-14.3%) for Greek and 5.2% (95% CI 2.7-7.6%) for Bulgarian pupils. The percentage of myopic children also differed between the two countries with the proportion with myopic refractive error