Monocular Contrast Research Articles

Binocular summation revisited: Beyond √2.

Our ability to detect faint images is better with two eyes than with one, but how great is this improvement? A meta-analysis of 65 studies published across more than 5 decades shows definitively that psychophysical binocular summation (the ratio of binocular to monocular contrast sensitivity) is significantly greater than the canonical value of √2. Several methodological factors were also found to affect summation estimates. Binocular summation was significantly affected by both the spatial and temporal frequency of the stimulus, and stimulus speed (the ratio of temporal to spatial frequency) systematically predicts summation levels, with slow speeds (high spatial and low temporal frequencies) producing the strongest summation. We furthermore show that empirical summation estimates are affected by the ratio of monocular sensitivities, which varies across individuals, and is abnormal in visual disorders such as amblyopia. A simple modeling framework is presented to interpret the results of summation experiments. In combination with the empirical results, this model suggests that there is no single value for binocular summation, but instead that summation ratios depend on methodological factors that influence the strength of a nonlinearity occurring early in the visual pathway, before binocular combination of signals. Best practice methodological guidelines are proposed for obtaining accurate estimates of neural summation in future studies, including those involving patient groups with impaired binocular vision.

Binocular temporal visual processing in myopia.

Our ability to utilize binocular visual information depends on the visibility of the retinal images in each eye, which varies with both their spatial and temporal frequency content. Although the effects of spatial information on binocular function have been established, the effects of temporal frequency on binocularity are less well understood. These factors may also vary with refractive error if spatiotemporal sensitivity is affected by structural changes during the emmetropization process that may differentially affect distinct ganglion cells. In a cross-sectional study, we evaluated the potential effects of temporal and spatial frequency on binocularity in young individuals with emmetropia or myopia. Stereopsis and binocular balance were measured as a function of temporal (0–12 Hz) and spatial (1–8 c/deg) frequency. Stereopsis thresholds were measured by determining the minimum disparity at which subjects accurately identified the depth of bandpass-filtered rings. Binocular balance was measured by determining the relative contrast at which subjects reported dichoptic bandpass-filtered letters with equal frequency. Stereopsis thresholds were temporal but not spatial frequency dependent whereas binocular balance was spatial and temporal frequency dependent. There were no differences in monocular spatiotemporal contrast sensitivity between refractive groups in our sample. However, individuals with myopia showed reduced stereopsis with flickering stimuli and greater binocular imbalance at higher spatial and lower temporal frequencies compared to emmetropes. Differences in binocular vision between emmetropia and corrected myopia depend on temporal as well as spatial frequency and may be the cause or consequence of abnormal emmetropization during visual development.

On Sensory Eye Dominance Revealed by Binocular Integrative and Binocular Competitive Stimuli.

PurposeTwo core processes underlie 3-D binocular vision. The first, a binocular combination/summation process, integrates similar feature signals from the two eye channels to form a binocular representation. The second, a binocular inhibitory process, suppresses interocular conflicting signals or falsely matched binocular representations to establish single vision. Having an intrinsic interocular imbalance within one or both processes can cause sensory eye dominance (SED), related to imbalances of combination (SEDcombo) and/or inhibition (SEDinhibition). While much has recently been revealed about SEDcombo and SEDinhibition, the relationship between them is still unknown.MethodsWe measured observers' foveal SEDcombo and SEDinhibition, respectively, with a pair of dichoptic horizontal sine wave gratings with different phases and binocular rivalry stimulus with vertical and horizontal gratings. We then measured horizontal and vertical monocular contrast thresholds using sinusoidal grating stimuli, and stereo thresholds using random-dot stereograms.ResultsThere exists a strong correlation between SEDcombo and SEDinhibition. An observer's interocular difference in contrast threshold was not always consistent with his/her SEDcombo and SEDinhihition, suggesting a partial binocular origin for the underlying imbalances. We also found stereo thresholds significantly increased with the magnitudes of SEDcombo, as well as with the magnitude of SEDinhibition.ConclusionsOur findings suggest a common origin for interocular imbalance in the two different binocular processes and that both types of sensory eye dominance are significant factors in impeding stereopsis.

Binocular contrast summation and inhibition depends on spatial frequency, eccentricity and binocular disparity.

When central vision is compromised, visually-guided behaviour becomes dependent on peripheral retina, often at a preferred retinal locus (PRL). Previous studies have examined adaptation to central vision loss with monocular 2D paradigms, whereas in real tasks, patients make binocular eye movements to targets of various sizes and depth in 3D environments. We therefore examined monocular and binocular contrast sensitivity functions with a 26-AFC (alternate forced choice) band-pass filtered letter identification task at 2° or 6° eccentricity in observers with simulated central vision loss. Binocular stimuli were presented in corresponding or non-corresponding stereoscopic retinal locations. Gaze-contingent scotomas (0.5° radius disks of pink noise) were simulated independently in each eye with a 1000 Hz eye tracker and 120 Hz dichoptic shutter glasses. Contrast sensitivity was higher for binocular than monocular conditions, but only exceeded probability summation at low-mid spatial frequencies in corresponding retinal locations. At high spatial frequencies or non-corresponding retinal locations, binocular contrast sensitivity showed evidence of interocular suppression. These results suggest that binocular vision deficits may be underestimated by monocular vision tests and identify a method that can be used to select a PRL based on binocular contrast summation.

Amblyopic Suppression: Passive Attenuation, Enhanced Dichoptic Masking by the Fellow Eye or Reduced Dichoptic Masking by the Amblyopic Eye?

To test the amblyopic suppression at mid to low spatial frequencies when compensating for signal attenuation. Eight amblyopes with (n = 5) or without (n = 3) strabismus and 10 normal controls with normal or corrected to normal visual acuity (≥20/20) and normal stereopsis (≤40 arcseconds) participated. Using a quick contrast sensitivity function approach, we measured individuals' monocular contrast sensitivity functions when the untested eye saw a mean luminance background and when the untested eye saw a bandpass filtered noise whose peak spatial frequency was matched to that of the test grating. Interocular suppression was quantified by the difference in thresholds occurring between these two conditions for each eye. The contrast of the noise mask was set at five times the threshold of the untested eye. Selected spatial frequencies (0.67-1.31 cyc/deg) were identified where neither ceiling (five times the mask contrast threshold in the amblyopic eye <100%) nor floor (threshold of the amblyopic eye when there was a noise mask in the fellow eye <100%) effects occurred for all observers. Within this frequency range, we found no interocular suppressive imbalance in normal observers. However, in amblyopes, the amblyopic eye exerted significantly less suppression than the fellow eye, while the suppression from the fellow eye to the amblyopic eye was similar to that found in the normal controls. We conclude that the reduced dichoptic masking by the amblyopic eye, within the context of normally balanced interocular inhibition, produces the amblyopic suppression at mid to low frequencies.

The effects of the age of onset of strabismus on monocular and binocular visual function in genetically identical twins

ObjectiveBoth genetic and environmental factors are thought to play a role in the pathogenesis of strabismus and subsequent ocular dominance and amblyopia. Our purpose was to compare the characteristics of sensory visual function in 2 adult monozygotic (genetically identical) twins who presented with esotropia at different ages. MethodsMonocular and binocular visual function was measured in the twins. Contrast sensitivity was used to assess monocular function. Suppressive and stereoscopic measurements were undertaken to assess binocular function. All tests were run using a 2-alternative forced choice psychophysical procedure. Eighteen short tandem repeats (STR) were genotyped across the genome in both twins to determine their exact relationship. ResultsTwin 1 (nondominant eye OD) was diagnosed with esotropia at 6 months of age, whereas twin 2 (nondominant eye OS) was diagnosed with esotropia at 5 years of age. They underwent a similar corrective surgical intervention soon after diagnosis to correct their esodeviations. Monocular contrast sensitivity was poorer for twin 1, particularly at intermediate spatial frequencies. In addition, twin 1 demonstrated complete suppression and unmeasurable stereoscopic function (>300 seconds). On the other hand, twin 2 demonstrated fusion, exhibited only mild suppression, and had near-normal (28 seconds) stereoscopic function. All STR alleles were identical in the twins, proving monozygosity. ConclusionsSensory measurements of monocular and binocular visual function in these genetically proven monozygotic twins were significantly different, with the earlier onset of esotropia associated with reduced visual function. Twin 2, whose esotropia was diagnosed at the age of 5 years, had near-normal visual function, both monocularly and binocularly. To the best of our knowledge, this represents the first study of a genetically identical sibling pair with strabismus. By eliminating the genetic differences between these patients, we are able to make powerful observations about the effect of environment on visual function in strabismus.

A Normative Data Set for the Clinical Assessment of Achromatic and Chromatic Contrast Sensitivity Using a qCSF Approach.

The measurement of achromatic sensitivity has been an important tool for monitoring subtle changes in vision as the result of disease or response to therapy. In this study, we aimed to provide a normative data set for achromatic and chromatic contrast sensitivity functions within a common cone contrast space using an abbreviated measurement approach suitable for clinical practice. In addition, we aimed to provide comparisons of achromatic and chromatic binocular summation across spatial frequency. We estimated monocular cone contrast sensitivity functions (CCSFs) using a quick Contrast Sensitivity Function (qCSF) approach for achromatic as well as isoluminant, L/M cone opponent, and S cone opponent stimuli in a healthy population of 51 subjects. We determined the binocular CCSFs for achromatic and chromatic vision to evaluate the degree of binocular summation across spatial frequency for these three different mechanisms in a subset of 20 subjects. Each data set shows consistent contrast sensitivity across the population. They highlight the extremely high cone contrast sensitivity of L/M cone opponency compared with the S-cone and achromatic responses. We also find that the two chromatic sensitivities are correlated across the healthy population. In addition, binocular summation for all mechanisms depends strongly on stimulus spatial frequency. This study, using an approach well suited to the clinic, is the first to provide a comparative normative data set for the chromatic and achromatic contrast sensitivity functions, yielding quantitative comparisons of achromatic, L/M cone opponent, and S cone opponent chromatic sensitivities as a function of spatial frequency.

The effects of monocular training on binocular functions in anisometropic amblyopia

Intensive monocular perceptual learning can improve visual acuity, contrast sensitivity, and vernier acuity in the amblyopic eye in adults with amblyopia. It is however not clear how much monocular training can enhance binocular visual functions. In the current study, we aimed to evaluate effects of monocular training on a variety of binocular functions. Nineteen anisometropic amblyopes (18.5±1.26yrs, mean±s.e.) were trained in a grating contrast detection task near each individual’s cutoff spatial frequency for 6–10days (630 trials/day). Visual acuity, stereoacuity, monocular and binocular contrast sensitivity functions (CSF), binocular phase combination and binocular rivalry were tested before and after training. Although monocular training can improve visual acuity and contrast sensitivity and eye dominance of the amblyopic eye, the magnitudes of improvements did not correlate with each other; the impact of monocular training on binocular phase combination was not significant. The results strongly suggest that structured monocular and binocular training is needed to fully recover deficient visual functions in anisometropic amblyopia.

The Effect of Acupuncture on Visual Function in Patients with Congenital and Acquired Nystagmus.

Background: The aim of this study is to examine the short-term effect of visual function following acupuncture treatment in patients with congenital idiopathic nystagmus and acquired nystagmus (CIN and AN). Methods: An observational pilot study on six patients with confirmed diagnosis of nystagmus (three CIN and three AN patients (2♀, 4♂; mean age 42.67; SD ± 20.57 y)), was performed. Acupuncture treatment was done following a standardized protocol applying needle-acupuncture on the body and the ears. The treatment was scheduled with 10 sessions of 30 min duration over five weeks. To assess the effect of the treatment, we performed before, between, and after acupuncture objective measurement of the BCVA (EDTRS charts), contrast vision (CSV-1000, Vector Vision), nystagmography (Compact Integrated Pupillograph), complemented by evaluation questionnaires. A placebo non-acupuncture control group (Nr: 11, 22 eyes; 8♀, 3♂; mean age: 33.34 y (SD ± 7.33 y)) was taken for comparison. Results: The results showed that, following acupuncture treatment, CIN and AN patients showed improvement (SD± mean) in their binocular BCVA (baseline: 0.45 ± 0.36; between: 0.53 ± 0.34 and post-treatment: 0.51 ± 0.28), and in their monocular contrast sensitivity (baseline: 11.29 ± 12.35; between: 11.43 ± 11.45 and post-treatment: 14.0 ± 12.22). The post-/baseline-difference showed a significant improvement in contrast vision and in BCVA for CIN and AN patients, but not for controls (p = 0.029 and p = 0.007, respectively). The effect of the eye showed also, within CIN and AN, significant values for the examined parameters in the post-/baseline difference (p = 0.004 and p ≤ 0.001). Evaluated only binocularly, the respective between-/baseline and post-/baseline difference in the CIN and AN group showed significant values (p < 0.045). Two AN patients reported reduction of oscillations. Among general subjective symptoms, our patients reported reduction of tiredness and headache attacks, improvement of vision, and shorter sleep onset time. Conclusion: The applied acupuncture protocol showed improvement in the visual function of nystagmus patients and thus, in their quality of life. Further studies are mandatory to differentiate which group of nystagmus patients would benefit more from acupuncture.

Factors Affecting Contrast Sensitivity in Healthy Individuals: A Pilot Study.

Objectives:To determine the demographic and ocular features affecting contrast sensitivity levels in healthy individuals.Materials and Methods:Seventy-four eyes of 37 subjects (7-65 years old) with refractive errors less than 1.0 diopter, no history of ocular surgery, and 20/20 visual acuity were included in the study. The participants were divided by age into three groups: group 1, 7-19 years, n=11; group 2, 20-49 years, n=15; and group 3, 50-65 years, n=11. All subjects underwent anterior and posterior segment evaluation, intraocular pressure measurements, refraction measurements, and clinical evaluation for strabismus. Contrast static test was performed using Metrovision MonPack 3 vision monitor system after measuring pupil diameter. Photopic and mesopic measurements were taken sequentially from right eyes, left eyes, and both eyes together.Results:Contrast sensitivity at intermediate and high spatial frequencies was lower with increasing age. Binocular measurements were better than monocular, and mesopic measurements were better than photopic measurements at all spatial frequencies. Contrast sensitivity at higher spatial frequency was lower with hyperopic refraction values.Conclusion:Increasing age, small pupil diameter, hyperopia, and photopic conditions were associated with lower contrast sensitivity in healthy individuals. Binocular contrast sensitivity measurements were better than monocular contrast sensitivity measurements in all conditions and spatial frequencies.

Effects of Monocular Blur on Clinical Measurements of Stereopsis and Binocular Contrast Sensitivity

Visual conditions such as anisometropia, monovision and monocular undercorrection affect the combination of visual input from both eyes. This study investigated the effects of monocular blur, in binocularly normal participants, on stereoacuity and binocular contrast sensitivity. Fifteen young adults (age range between 19 and 23 years old) with normal visual acuity and binocular vision participated in this study. Stereopsis was measured using the TNO test with a series of positive spherical lenses placed before the dominant eye. The procedure was repeated using the Titmus Stereotest on five participants as a control experiment. Monocular and binocular contrast sensitivities were also measured using the Pelli-Robson Contrast Sensitivity Chart. Blur was induced monocularly with a series of positive spherical lenses placed before the dominant eye and binocular contrast sensitivity was re-measured. Stereopsis scores decreased significantly when monocular blur was imposed. Across blur levels, absolute stereopsis scores measured with TNO test were worse than those measured with Titmus stereotest (all p < 0.05). However, the ratio of scores obtained without blur and under monocular blur appeared to be similar for both tests. Stereopsis without blur was between 6.82× to 8× better than that obtained with the highest level of imposed monocular blur. Binocular contrast sensitivity score decreased significantly with increasing level of monocular blur (p < 0.01). Binocular contrast sensitivity score without blur was 1.62× better than that obtained under binocular viewing with highest level of imposed blur. Stereopsis tests are more sensitive than measurements of binocular contrast sensitivity as an indicator of interocular acuity discrepancies which could occur in anisometropic or monovision patients. However, the choice of stereopsis test is crucial, as the TNO test appears to be more sensitive to monocular blur than the Titmus stereostest. DOI: http://dx.doi.org./10.17576/JSKM-2017-1501-03

Effect of Rigid Gas Permeable Contact Lenses on Nystagmus and Visual Function in Hyperopic Patients with Infantile Nystagmus Syndrome

ABSTRACTPurpose: To determine the effect of rigid gas permeable contact lenses (RGPCL) on involuntary eye movements and visual function in hyperopic patients with infantile nystagmus syndrome. Methods: This prospective interventional case series was conducted on 16 patients with infantile nystagmus and hyperopia equal or more than +0.5 D and astigmatism more than -1 D over a 2-year period. A complete ophthalmological examination including determination of best corrected visual acuity (BCVA), contrast sensitivity, and videonystagmography was performed for all patients before and after at least 3 months of RGPCL use, and the outcomes were compared. Results: Thirty-two eyes of 16 patients with mean age of 18.6±4.9 years were enrolled. Mean spherical equivalent refractive error was +1.5±2.35 (range +1 to +6.25) diopters (D); corresponding values were +2.45±2.44 D (range +0.5 to +7.5) for spherical error and +1.90±0.83 D (range +1 to +4) for astigmatism. Monocular BCVA improved from 0.56±0.23 to 0.51±0.23 Log MAR (P=0.007), and binocular BCVA improved from 0.54±0.25 to 0.48±0.24 Log MAR (P=0.01) after fitting RGPCL. Following the use of RGPCL, contrast sensitivity was significantly improved at low (P=0.02) and intermediate (P< 0.001) frequencies but not at high frequencies (P=0.6). The frequency, amplitude, and intensity of nystagmus were decreased significantly after RGPCL use (P<0.001). Conclusion: RGPCL improved monocular and binocular BCVA and contrast sensitivity in hyperopic patients with infantile nystagmus syndrome. Motor indices of nystagmus (frequency, amplitude, and intensity) were also significantly improved after RGPCL use.

High and Low Contrast Visual Acuity Are Not Affected in Amyotrophic Lateral Sclerosis.

The afferent visual system may be affected by neuro-degeneration in amyotrophic lateral sclerosis (ALS) based on observations of visual function impairment and retinal inclusions on histopathology in ALS patients. To test the hypothesis that visual acuity is impaired in ALS, we compared three measures of visual acuity in ALS patients (n = 25) attending a multidisciplinary ALS clinic and age matched control subjects (n = 25). Bilateral monocular and binocular visual acuities were assessed using high contrast (black letters on white background) and low contrast (2.5%, 1.25% grey letters on white background) visual acuity charts under controlled lighting conditions following refraction. Binocular summation was calculated as the difference between binocular and best monocular acuity scores. There were no associations between binocular or monocular high contrast visual acuity or low contrast visual acuity and amyotrophic lateral sclerosis diagnosis (generalized estimating equation models accounting for age). Binocular summation was similar in both amyotrophic lateral sclerosis and control subjects. There was a small magnitude association between increased duration of ALS symptoms and reduced 1.25% low contrast visual acuity. This study does not confirm prior observations of impaired visual acuity in patients with amyotrophic lateral sclerosis and does not support this particular measure of visual function for use in broad scale assessment of visual pathway involvement in ALS patients.

Flicker adaptation and neural transmission speed in the human MC pathway

INTRODUCTION: Flicker-induced adaptation of the human magnocelluar (MC) pathway increases contrast thresholds (Zhuang, Pokorny & Cao, IOVS 2015). This study tests whether flicker adaptation also reduces neural transmission speed for suprathreshold stimuli by measuring the response time to a suprathreshold disc. The working hypotheses are that (#1) flicker presented to a given eye can adapt the monocular pathway and also a subsequent binocular mechanism and (#2) flicker presented to both eyes causes greater adaptation at the binocular level than flicker to only one eye. METHODS: Adaptation was induced with a flickering 16x13 deg rectangular field modulated at 9.4 Hz with 100% Michelson contrast. Adaptation could be in neither eye (baseline using a steady adapting field), in only one eye or in both eyes. The test stimulus for response time, a foveal 0.5 deg diameter disc, could be presented to either eye alone or both eyes. Observers responded to the test stimulus as quickly as possible. RESULTS AND DISCUSSION: Response time was the slowest when a monocular test stimulus was presented to the same monocularly adapted eye. Surprisingly, with a monocular test the response time was significantly faster with binocular adaptation than with same-eye monocular adaptation. This suggests that when both eyes are adapted to flicker, the overall adapting effect for a monocular test is inhibited by flicker adaptation in the fellow eye. Overall, the results confirm that flicker adaptation reduces neural transmission speed for suprathreshold stimuli (consistent with working hypothesis #1), but also show that transmission speed for a stimulus presented to only one eye can be speeded up by adding adaptation in the fellow eye (contrary to #2). The latter finding corroborates a similar conclusion from measurements of monocular and binocular contrast thresholds (Zhuang & Shevell, Vision Research 2015). Meeting abstract presented at VSS 2016

Photopic and Mesopic Performance of 2 Different Trifocal Diffractive Intraocular Lenses.

Purpose To assess photopic and mesopic vision in patients implanted with 2 different trifocal intraocular lenses (IOLs). Methods Fifty patients with cataract in both eyes had surgery with bilateral implantation of a trifocal FineVision (FV, n = 25) or AT LISA tri 839MP (LisaTri, n = 25) IOL. Three months after surgery, high-contrast photopic uncorrected distance visual acuity and corrected distance visual acuity (CDVA) were determined using the Early Treatment Diabetic Retinopathy Study test. Intermediate (65 cm) and near (40 cm) visual acuity were also measured, both with best distance correction (DCIVA and DCNVA, respectively). The CSV1000 test chart was used for binocular and monocular contrast sensitivity. Defocus curves were constructed under photopic and mesopic conditions. Results Mean patient age was 68.4 ± 5.5 years (FV) and 67.3 ± 5.6 years (LisaTri) (p = 0.540). No differences were found in terms of visual acuity between the groups. The CDVA, DCIVA, and DCNVA were 0.05 ± 0.06, 0.25 ± 0.10, and 0.13 ± 0.10 logMAR for FV and -0.04 ± 0.11, 0.32 ± 0.09, and 0.12 ± 0.11 logMAR for LisaTri, respectively (p = 0.09, p = 0.08, and p = 0.12). Photopic and mesopic defocus curves were comparable between the 2 IOL groups (p>0.05). Mesopic values were significantly worse than photopic in both groups for all the measured values (p<0.001). No differences in contrast sensitivity were observed between the 2 IOL groups (p>0.05). Conclusions Both trifocal diffractive IOLs provided good visual quality with a statistically significant decrease in mesopic conditions.

Binocular contrast discrimination needs monocular multiplicative noise.

The effects of signal and noise on contrast discrimination are difficult to separate because of a singularity in the signal-detection-theory model of two-alternative forced-choice contrast discrimination (Katkov, Tsodyks, & Sagi, 2006). In this article, we show that it is possible to eliminate the singularity by combining that model with a binocular combination model to fit monocular, dichoptic, and binocular contrast discrimination. We performed three experiments using identical stimuli to measure the perceived phase, perceived contrast, and contrast discrimination of a cyclopean sine wave. In the absence of a fixation point, we found a binocular advantage in contrast discrimination both at low contrasts (<4%), consistent with previous studies, and at high contrasts (≥34%), which has not been previously reported. However, control experiments showed no binocular advantage at high contrasts in the presence of a fixation point or for observers without accommodation. We evaluated two putative contrast-discrimination mechanisms: a nonlinear contrast transducer and multiplicative noise (MN). A binocular combination model (the DSKL model; Ding, Klein, & Levi, 2013b) was first fitted to both the perceived-phase and the perceived-contrast data sets, then combined with either the nonlinear contrast transducer or the MN mechanism to fit the contrast-discrimination data. We found that the best model combined the DSKL model with early MN. Model simulations showed that, after going through interocular suppression, the uncorrelated noise in the two eyes became anticorrelated, resulting in less binocular noise and therefore a binocular advantage in the discrimination task. Combining a nonlinear contrast transducer or MN with a binocular combination model (DSKL) provides a powerful method for evaluating the two putative contrast-discrimination mechanisms.

Multifocal corneal ablation (Supracor) in hyperopic presbyopia: 1-year results in a cross-sectional study.

To evaluate the efficacy and safety of the multifocal excimer laser corneal ablation profile (the Supracor procedure) in hyperopic presbyopia 1 year after laser treatment. This prospective, consecutive, one-center, cross-sectional study included 20 patients with hyperopic presbyopia 1 year after treatment with the Supracor procedure. The main outcome measures were monocular uncorrected distance visual acuity (UDVA) and uncorrected near visual acuity (UNVA), photopic contrast sensitivity (Pelli-Robson charts), patient satisfaction, and functioning at 12 months. Thirty-nine eyes of 20 patients (mean age 59 ± 7.2 years) were treated. Mean UDVA improved from 0.56 ± 0.31 (mean 0.34 logMAR) preoperatively to 0.9 ± 0.15 (mean 0.06 logMAR) 12 months after surgery. Mean UNVA increased from 0.15 ± 0.07 (mean 0.84 logMAR) before surgery to 0.62 ± 0.24 (mean 0.23 logMAR) 12 months after treatment. Four eyes lost 2 lines of corrected distance visual acuity (10.3%). Monocular photopic contrast sensitivity was within age-correlated normal range (Pelli-Robson chart, mean contrast sensitivity 1.83 ± 0.18). A total of 75% of the patients would undergo Supracor again (1 not, 4 perhaps). The most frequently reported side effects were increased glare, reduced distance vision, and fluctuations in vision. Most patients used artificial tears. One year after Supracor, UDVA and UNVA improved markedly, photopic contrast sensitivity was in normal age-correlated range, and the majority of patients (75%) was satisfied with the results. Side effects like loss of distance vision, fluctuations of vision, and increased glare have a greater influence on patient satisfaction than the improvement of spectacle-free near vision.

Effect of Photorefractive Keratectomy on Nystagmus and Visual Functions in Myopic Patients With Infantile Nystagmus Syndrome

To determine the effect of photorefractive keratectomy (PRK) on involuntary eye movements, visual acuity, and contrast sensitivity in myopic patients with infantile nystagmus syndrome. Prospective interventional case series. This study was conducted on patients with infantile nystagmus syndrome and myopia equal to or more than-1 diopter (D), who were referred to our clinic over a 2-year period. Patients older than 18 years of age with a stable refraction for at least 1 year who were good candidates for PRK were included. Complete ophthalmologic examinations including assessment of best-corrected visual acuity (BCVA), contrast sensitivity, and videonystagmography were performed for all patients before and 3months after surgery. Twenty-four eyes of 12 patients with mean age of 23 ± 2 years were enrolled in this study. Spherical equivalent refractive error was-2.82 ± 1.65 D and-0.26 ± 0.25 D before and after PRK, respectively (P < .001). Monocular BCVA improved from 0.36 ± 0.21 logMAR to 0.27 ± 0.25 logMAR and binocular BCVA improved from 0.33 ± 0.2 logMAR to 0.17 ± 0.16 logMAR (P < .001). Contrast sensitivity significantly improved at low (P < .001), intermediate (P<.001), and high frequencies (P= .01). The frequency, amplitude, and intensity of nystagmus were significantly decreased after PRK (P < .001). There was no correlation between the degree of myopia correction and improvement in sensory and motor indicesof nystagmus (P > .1, Spearman correlation coefficient). PRK in patients with infantile nystagmus syndrome and myopia improved monocular and binocular BCVA and contrast sensitivity. Furthermore, motor indices of nystagmus (frequency, amplitude, and intensity) were significantly improved after surgery in these patients.

Effectiveness of Technolas torsional eye tracking system on visual outcomes after photorefractive keratectomy.

PurposeTo investigate the efficacy of Technolas 217Z eye tracking system (torsional component) in corneal surface irregularity and high order aberrations (HOAs) after photorefractive keratectomyMethodsPatients with compound myopic astigmatism among persons demanding refractive surgery in Khatam-al-Anbia Eye Hospital with the mean age of 29 years were enrolled in this double-blind randomized interventional study. The mean spherical equivalent (SE) of refractive error was −4.75 diopters(D) (range: −1.5 to −7.0), and the mean astigmatism was 3 D (range:1.0–4). Many studies were performed for each patient including: A complete eye examination, visual acuity and Monocular contrast sensitivity evaluation, and refraction. Corneal topography, Orbscan II, and wavefront aberrometry were conducted. One eye was randomly assigned for aspheric treatment and applying eye tracking system. The other eye was treated without torsional eye tracking system. The outcome measures were uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), contrast sensitivity, corneal irregularity index in 3 mm and 5 mm optical zones in Orbscan II, and mean total HOAs at the 6-monthvisit.ResultsFifty eyes of 25 patients were enrolled. Mean UCVA was improved significantly in both the study and control groups in the 6-month post-operative follow-up. There was no significant difference between the 2 groups in UCVA and BCVA (P = 0.185 and P = 0.176, respectively). Total HOAs increased in both groups after PRK. However, they were lower in eyes treated with the eye tracking system (P < 0.001). Corneal irregularity index in 3 mm and 5 mm central zones in Orbscan II was significantly lower in the study group (P = 0.045 and P = 0.031 respectively). Contrast sensitivity function was not different in the 2 groups (P = 0.15).ConclusionOur study findings suggest that applying ‘Technolas 217z’ eye tracker system (Bausch and Lomb Advanced) results in a more regular anterior surface of cornea. Therefore, we recommend it for surface laser refractive surgery.

Comparative analysis of the visual performance and aberrometric outcomes with a new hybrid and two silicone hydrogel multifocal contact lenses: a pilot study

BackgroundThe aim was to evaluate the visual performance achieved with a new multifocal hybrid contact lens and to compare it with that obtained with two other currently available multifocal soft contact lenses.MethodsThis pilot prospective comparative study comprised a total of 16 presbyopic eyes of eight patients ranging in age from 43 to 58 years. All patients were fitted with three different models of multifocal contact lens: Duette multifocal (SynergEyes), Air Optix AQUA multifocal (Alcon) and Biofinity multifocal (CooperVision). Fittings were performed randomly in each patient according to a random number sequence, with a wash‐out period between fittings of seven days. At two weeks post‐fitting, visual, photopic contrast sensitivity and ocular aberrometry were evaluated.ResultsNo statistically significant differences were found in distance and near visual acuity achieved with the three different types of multifocal contact lens (p ≥ 0.05). Likewise, no significant differences between lenses were found in the monocular and binocular defocus curve (p ≥ 0.10). Concerning contrast sensitivity, better monocular contrast sensitivities for 6, 12 and 18 cycles per degree were found with the Duette and Air Optix multifocal compared to Biofinity (p = 0.02). Binocularly, differences between lenses were not significant (p ≥ 0.27). Furthermore, trefoil aberration was significantly higher with Biofinity multifocal (p < 0.01) and Air Optix (p = 0.01) multifocal compared to Duette.ConclusionsThe Duette multifocal hybrid contact lens seems to provide similar visual quality outcomes in presbyopic patients with low corneal astigmatism, when compared with other soft multifocal contact lenses. This preliminary result should be confirmed in studies with larger samples.