Trisevgeni Giannakopoulou

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.

Interocular differences in visual latency induced by reduced-aperture monovision

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.

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.

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.

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/m2. Results Interocular differences in monocular VEP latency (at 30 cd/m2) 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/m2 (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

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.

Mechanical optic neuropathy in high myopia

Myopia is a major cause of visual impairment and its prevalence is increasing globally at an alarming rate. High pathologic myopia is described as myopia with associated degenerative changes in the sclera, choroid and retinal pigment epithelium, resulting initially in loss of visual acuity (VA). Excessive elongation of the globe and posterior staphyloma are the hallmark findings in pathological myopia leading to mechanical damage to the retina and the optic nerve as a result of global stretching. Lacquer cracks, representing mechanical breaks of Bruch’s membrane are a typical manifestation of mechanical stretching in high myopic eyes. Moreover, papillary and peripapillary regions are often distorted because of the mechanical stress caused by an elongated myopic eye causing tilted optic discs and acquired megalodiscs. This report describes a case of a 43-yearold Caucasian man with pathological myopia who reported decreased vision in his right eye after an airplane landing. Imaging and clinical workup revealed excessive globe elongation potentially leading to optic nerve dysfunction.