Changes In Contrast Sensitivity Research Articles

Contrast sensitivity and the effect of 60-hour sleep deprivation.

The study aimed to evaluate the possible influence of prolonged sleep deprivation on achromatic and chromatic (red-green and blue-yellow) contrast sensitivity (CS). During 60-hr sleep deprivation, CS was measured in 11 naval officers every sixth hour using videographic (Vigra-C) sine-wave-generated stimuli. When comparing the CS measurements obtained in the first and last 24 hr of the study, no statistically significant mean changes of achromatic CS (2.0, 5.9 and 11.8 cpd) or yellow-blue CS (0.6, 2.0 and 4.7 cpd) were found, while a significantly increased mean red-green CS at 2.0 and 4.7 cpd was recorded in the last 24 hr (p = 0.003 in both). The variance of achromatic and chromatic CS measurements in the group did not differ significantly in the first and last 24 hr test periods. Prolonged sleep deprivation does apparently not cause clinically or occupationally significant changes of contrast sensitivity in otherwise healthy subjects with normal visual acuity.

Changes in color vision and contrast sensitivity after descemet membrane endothelial keratoplasty for fuchs endothelial dystrophy.

The aim of this study is to evaluate contrast sensitivity, color vision, and subjective patient satisfaction after Descemet membrane endothelial keratoplasty (DMEK) in patients with bilateral Fuchs endothelial dystrophy (FED). From a group of 500 DMEK surgeries performed in our center, patients with a history of bilateral FED and unilateral DMEK were identified. A total of 29 patients were included in the study and divided into 2 groups: phakic (n = 12) and pseudophakic unilateral DMEK (n = 17) and their contralateral, untreated FED-affected eye. In addition, a control group of 10 healthy eyes of 10 patients was included. Pelli-Robson contrast sensitivity and Farnsworth-Munsell 100 hue color vision tests were performed. Subjective optical quality was graded with a questionnaire. Compared with untreated FED-affected eyes, best spectacle-corrected visual acuity was higher after DMEK in phakic and pseudophakic eyes (P = 0.030 and P < 0.001, respectively); a similar result was obtained for contrast sensitivity (P < 0.001 and P < 0.001, respectively). Color vision did not differ between untreated FED-affected and DMEK-operated eyes in the phakic group (P = 0.802) and the pseudophakic group (P = 0.227). Subjective optical quality was better in DMEK-operated eyes than in untreated FED-affected eyes in the phakic group (P < 0.001) and in the pseudophakic group (P < 0.001). In FED, DMEK may not only be effective for obtaining a higher visual acuity but particularly improving the contrast sensitivity may also lead to better subjective optical performance. Although frequently mentioned spontaneously by patients, an objective change in color vision could not be substantiated. Hence, quantifying contrast sensitivity before surgery may aid in the decision for surgery, and in the evaluation of surgical outcome.

The relationship between contrast detection and saccadic reaction times with attention.

Visual spatial attention can increase contrast sensitivity and decrease saccadic or manual reaction times (RTs) in attended compared to unattended locations. As stimulus contrast also influences saccadic RT, we asked whether the effect of attention on saccadic RT can be accounted for by the change in contrast sensitivity. We used a dual task paradigm that recorded saccadic RTs and psychophysical responses to targets of various contrast. On each trial, subjects were presented with a central fixation stimulus, which also carried an endogenous cue (an arrow) to the target's radial direction but not its eccentricity. Across trials, the cue was 75% valid, 12.5 % invalid and 12.5 % neutral (no arrow). Circular gratings m-scaled for eccentricity were flashed for 8 ms in one of 8 radial directions around fixation, at either 3 or 6 deg eccentricity, with one of 9 contrasts. The subjects' tasks were to (1) saccade to the location where the target flashed and (2) respond via button press if the target flashed at the nearer (3 deg) or the farther (6 deg) eccentricity. Saccadic RTs and psychophysical responses to targets at the different contrast levels were analyzed to assess the effects of cueing. Valid cueing produced a factor of 1.2 increase in contrast sensitivity, relative to invalid-cue trials. Valid cueing also reduced saccadic RTs for contrast levels at and above the detection threshold. However, the effect of cueing on saccadic RT is accounted for only partly by the increase in psychophysical contrast sensitivity. A comparison of RT vs. contrast for valid and invalid cueing shows a combined effect: a shift consistent with the observed change in contrast sensitivity, and an overall change in latency of roughly 20 msec. Attention appears to influence saccadic RTs in more than one way. Meeting abstract presented at VSS 2014

Green light laser exposure at 532 nm near the exposure limit during a human volunteer vehicle driving task does not alter structure or function in the visual system

This study aimed to verify nonexistence of clinically important pathological effects to the visual system after exposure to 532 nm green laser light close to the exposure limit. The present medical surveillance of vision and visual health reported in this paper is the conjunction with a study of driver performance in the presence of 532 nm laser induced glare. The driving time varied between 25 and 55 s, depending on background luminance. The laser was on during the complete test drive. The peak corneal irradiance typically was 3.5 W·m−2 in one test drive. Considering a typical test drive, the typical time integrated corneal radiant exposure for one test drive was estimated to be 53 J·m−2. The number of test drives varied among drivers but was typically 50, thus resulting in a cumulative corneal exposure dose of approximately 2.7 kJ·m−2. Altogether, ten subjects were recruited according to inclusion and exclusion criteria. All ten subjects were examined for visual acuity, intraocular pressure, contrast sensitivity, color vision, monocular reading speed, and eye structure with clinical slit-lamp microscopy examination and indirect retinoscopy. All subjects were examined before exposure, immediately after exposure, and finally within an interval between 1 week and 4 weeks after exposure. There was no significant change of visual acuity, intraocular pressure, contrast sensitivity, color vision, or monocular reading speed between before and after exposure. No abnormal ocular structure was detected after exposure. This study demonstrates that close to exposure limit, exposure to 532 nm green laser light during a vehicle driving task does not induce structural or functional damage to the human visual system as observed in the interval minutes to weeks after exposure.

Acute effect of alcohol intake on sine-wave Cartesian and polar contrast sensitivity functions

The aim of this study was to assess contrast sensitivity for angular frequency stimuli as well as for sine-wave gratings in adults under the effect of acute ingestion of alcohol. We measured the contrast sensitivity function (CSF) for gratings of 0.25, 1.25, 2.5, 4, 10, and 20 cycles per degree of visual angle (cpd) as well as for angular frequency stimuli of 1, 2, 4, 24, 48, and 96 cycles/360°. Twenty adults free of ocular diseases, with normal or corrected-to-normal visual acuity, and no history of alcoholism were enrolled in two experimental groups: 1) no alcohol intake (control group) and 2) alcohol ingestion (experimental group). The average concentration of alcohol in the experimental group was set to about 0.08%. We used a paradigm involving a forced-choice method. Maximum sensitivity to contrast for sine-wave gratings in the two groups occurred at 4 cpd sine-wave gratings and at 24 and 48 cycles/360° for angular frequency stimuli. Significant changes in contrast sensitivity were observed after alcohol intake compared with the control condition at spatial frequency of 4 cpd and 1, 24, and 48 cycles/360° for angular frequency stimuli. Alcohol intake seems to affect the processing of sine-wave gratings at maximum sensitivity and at the low and high frequency ends for angular frequency stimuli, both under photopic luminance conditions.

Effect of Ginkgo Biloba on Visual Field and Contrast Sensitivity in Chinese Patients With Normal Tension Glaucoma: A Randomized, Crossover Clinical Trial

We evaluated the effect of ginkgo biloba extract on visual field defect and contrast sensitivity in a Chinese cohort with normal tension glaucoma. In this prospective, randomized, placebo-controlled crossover study, patients newly diagnosed with normal tension glaucoma, either in a tertiary glaucoma clinic (n = 5) or in a cohort undergoing routine general physical examinations in a primary care clinic (n = 30), underwent two 4-week phases of treatment, separated by a washout period of 8 weeks. Randomization determined whether ginkgo biloba extract (40 mg, 3 times per day) or placebo (identical-appearing tablets) was received first. Primary outcomes were change in contrast sensitivity and mean deviation on 24-2 SITA standard visual field testing, while secondary outcomes included IOP and self-reported adverse events. A total of 35 patients with mean age 63.7 (6.5) years were randomized to the ginkgo biloba extract-placebo (n = 18) or the placebo-ginkgo biloba extract (n = 17) sequence. A total of 28 patients (80.0%, 14 in each group) who completed testing did not differ at baseline in age, sex, visual field mean deviation, contrast sensitivity, IOP, or blood pressure. Changes in visual field and contrast sensitivity did not differ by treatment received or sequence (P > 0.2 for all). Power to have detected a difference in mean defect as large as previously reported was 80%. In contrast to some previous reports, ginkgo biloba extract treatment had no effect on mean defect or contrast sensitivity in this group of normal tension glaucoma patients. (http://www.chictr.org number, ChiCTR-TRC-08000724).

Exogenous spatial attention: evidence for intact functioning in adults with autism spectrum disorder.

Deficits or atypicalities in attention have been reported in individuals with autism spectrum disorder (ASD), yet no consensus on the nature of these deficits has emerged. We conducted three experiments that paired a peripheral precue with a covert discrimination task, using protocols for which the effects of covert exogenous spatial attention on early vision have been well established in typically developing populations. Experiment 1 assessed changes in contrast sensitivity, using orientation discrimination of a contrast-defined grating; Experiment 2 evaluated the reduction of crowding in the visual periphery, using discrimination of a letter-like figure with flanking stimuli at variable distances; and Experiment 3 assessed improvements in visual search, using discrimination of the same letter-like figure with a variable number of distractor elements. In all three experiments, we found that exogenous attention modulated visual discriminability in a group of high-functioning adults with ASD and that it did so in the same way and to the same extent as in a matched control group. We found no evidence to support the hypothesis that deficits in exogenous spatial attention underlie the emergence of core ASD symptomatology.

A Study of the Short-Term Effect of Artificial Tears on Contrast Sensitivity in Patients With Sjögren's Syndrome

Primary Sjögren's syndrome often includes dry eye manifestations, including a reduction in optical quality from the compromised ocular surface. This study was designed to measure the effect of different artificial tears on the contrast sensitivity of Sjögren's syndrome patients from 5 minutes to 4 hours after instillation. Ten normal subjects and 10 subjects with ocular manifestations of Sjögren's syndrome were compared at baseline, including staining scores, a dry eye questionnaire, and contrast sensitivity testing. Changes in contrast sensitivity in the Sjögren's syndrome group were measured over a 4-hour period after instillation of a variety of artificial tears. Statistically significant differences in staining, subjective questionnaire scores, and contrast sensitivity were measured between the normal and Sjögren's syndrome groups. Statistically significant changes in contrast sensitivity were measured over time after artificial tear instillation, with the greatest effect at 3 to 6 cycles/deg. The more mucoadhesive artificial tears demonstrated a significantly greater effect. The effects of artificial tears on measured contrast sensitivity in dry eye patients in the postinstillation period of 5 minutes to 4 hours appear limited, but an artificial tear with more mucoadhesive properties showed more benefit than those that do not. Modest effects on contrast sensitivity, primarily at medium spatial frequencies, were observed with the more mucoadhesive formulations.

Rapid and reliable assessment of the contrast sensitivity function on an iPad.

Letter acuity, the predominant clinical assessment of vision, is relatively insensitive to slow vision loss caused by eye disease. While the contrast sensitivity function (CSF) has demonstrated the potential to monitor the slow progress of blinding eye diseases, current tests of CSF lack the reliability or ease-of-use to capture changes in vision timely. To improve the current state of home testing for vision, we have developed and validated a computerized adaptive test on a commercial tablet device (iPad) that provides an efficient and easy-to-use assessment of the CSF. We evaluated the reliability, accuracy, and flexibility of tablet-based CSF assessment. Repeated tablet-based assessments of the spatial CSF, obtained from four normally-sighted observers, which each took 3 to 5 minutes, were compared to measures obtained on CRT-based laboratory equipment; additional tablet-based measures were obtained from six subjects under three different luminance conditions. A Bland-Altman analysis demonstrated that tablet-based assessment was reliable for estimating sensitivities at specific spatial frequencies (coefficient of repeatability 0.14-0.40 log units). The CRT- and tablet-based results demonstrated excellent agreement with absolute mean sensitivity differences <0.05 log units. The tablet-based test also reliably identified changes in contrast sensitivity due to different luminance conditions. We demonstrate that CSF assessment on a mobile device is indistinguishable from that obtained with specialized laboratory equipment. We also demonstrate better reliability than tests used currently for clinical trials of ophthalmic therapies, drugs, and devices.

Four-Year Visual, Refractive, and Contrast Sensitivity Outcomes After Wavefront-Guided Myopic LASIK Using an Advanced Excimer Laser Platform

To evaluate the 4-year visual, refractive, and contrast sensitivity outcomes of wavefront-guided LASIK for the correction of low to moderate myopia using the VISX CustomVue technology (Abbott Medical Optics, Inc., Santa Ana, CA). This was a prospective study including 255 consecutive eyes of 145 patients (age range: 19 to 55 years) with low to moderate myopia (mean spherical equivalent: -3.36 ± 1.71 diopters [D]) undergoing laser refractive surgery. Wavefront-guided LASIK was performed in all eyes using the VISX STAR S4 IR excimer laser platform and the CustomVue procedure for the ablation profile design. Visual, refractive, and contrast sensitivity changes were evaluated during a 4-year follow-up period. Postoperative logMAR uncorrected distance visual acuity was 0.1 or better (20/25 Snellen) in 98.0% and 100% of eyes at 1 and 4 years, respectively. At 4 years postoperatively, mean spherical equivalent was reduced significantly to a mean value of -0.22 ± 0.28 D (P < .01), with 97.3% of eyes with a spherical equivalent within ±0.50 D. The astigmatic power vector component J0 of manifest refraction was also reduced significantly (P < .01). Postoperative logMAR corrected distance visual acuity was 0.0 or better (20/20 Snellen) in 96.1% and 98.8% of eyes at 1 and 4 years, respectively. Improvement in contrast sensitivity was observed in some spatial frequencies between 1 and 4 years postoperatively. No significant correlations were found between 4-year contrast sensitivity and corrected distance visual acuity (0.024 ≤ r ≤ -0.120, P ≥ .06). Wavefront-guided LASIK using the VISX CustomVue technology provides an effective and predictable correction of low to moderate myopia in the long term, preserving the patient's visual acuity and quality.

Longitudinal measurements of luminance and chromatic contrast sensitivity: comparison between wavefront-guided LASIK and contralateral PRK for myopia

The present study aimed to compare the postoperative contrast sensitivity functions between wavefront-guided LASIK eyes and their contralateral wavefront-guided PRK eyes. The participants were 11 healthy subjects (mean age=32.4 ± 6.2 years) who had myopic astigmatism. The spatial contrast sensitivity functions were measured before and three times after the surgery. Psycho and a Cambridge graphic board (VSG 2/4) were used to measure luminance, red-green, and blue-yellow spatial contrast sensitivity functions (from 0.85 to 13.1 cycles/degree). Longitudinal analysis and comparison between surgeries were performed. There was no significant contrast sensitivity change during the one-year follow-up measurements neither for LASIK nor for PRK eyes. The comparison between procedures showed no differences at 12 months postoperative. The present data showed similar contrast sensitivities during one-year follow-up of wave-front guided refractive surgeries. Moreover, one year postoperative data showed no differences in the effects of either wavefront-guided LASIK or wavefront-guided PRK on the luminance and chromatic spatial contrast sensitivity functions.

Capturing Age-Related Changes in Functional Contrast Sensitivity With Decreasing Light Levels in Monocular and Binocular Vision

It is challenging to separate the effects of normal aging of the retina and visual pathways independently from optical factors, decreased retinal illuminance, and early stage disease. This study determined limits to describe the effect of light level on normal, age-related changes in monocular and binocular functional contrast sensitivity. We recruited 95 participants aged 20 to 85 years. Contrast thresholds for correct orientation discrimination of the gap in a Landolt C optotype were measured using a 4-alternative, forced-choice (4AFC) procedure at screen luminances from 34 to 0.12 cd/m(2) at the fovea and parafovea (0° and ±4°). Pupil size was measured continuously. The Health of the Retina index (HRindex) was computed to capture the loss of contrast sensitivity with decreasing light level. Participants were excluded if they exhibited performance outside the normal limits of interocular differences or HRindex values, or signs of ocular disease. Parafoveal contrast thresholds showed a steeper decline and higher correlation with age at the parafovea than the fovea. Of participants with clinical signs of ocular disease, 83% had HRindex values outside the normal limits. Binocular summation of contrast signals declined with age, independent of interocular differences. The HRindex worsens more rapidly with age at the parafovea, consistent with histologic findings of rod loss and its link to age-related degenerative disease of the retina. The HRindex and interocular differences could be used to screen for and separate the earliest stages of subclinical disease from changes caused by normal aging.

Changes in Contrast Sensitivity after Surgery for Macula-On Rhegmatogenous Retinal Detachment

To evaluate changes in contrast sensitivity after surgery for macula-on rhegmatogenous retinal detachment (RRD). Prospective, interventional, consecutive, case-control study. This study included 84 eyes of 84 patients with unilateral macula-on RRD undergoing primary scleral buckling or vitrectomy without postoperative macular complication. We examined the logarithm of the minimal angle of resolution best-corrected visual acuity (logMAR BCVA) and contrast sensitivity at 4 spatial frequencies (3, 6, 12, and 18 cycles/degree) using the CSV-1000E (Vector Vision) before and after surgery. From the data obtained with the CSV-1000E, the area under the log contrast sensitivity function was calculated. The logMAR BCVA and contrast sensitivity in the contralateral normal eyes also were measured and were used as normal controls. Clinical data were collected, including age, gender, surgical procedures, the number of retinal tears, circumferential dimension of retinal tears, and area of retinal detachment, to determine the clinical factors related to visual function. Preoperative contrast sensitivity was significantly worse in eyes with RRD than in normal controls, but the preoperative logMAR BCVA was not different from that of normal controls. Contrast sensitivity decreased significantly after surgery, but logMAR BCVA did not change by surgery. Multiple regression analysis revealed that postoperative contrast sensitivity had a significant correlation with the circumferential dimension of retinal tears, whereas no clinical parameters were associated significantly with postoperative BCVA. Surgery for macula-on RRD did not change visual acuity, whereas contrast sensitivity was affected significantly in association with the extent of retinal tears.

Punctal plugs versus artificial tears for treating primary Sjögren’s syndrome with keratoconjunctivitis SICCA: a comparative observation of their effects on visual function

To compare the effects of treatment with punctal plugs versus artificial tears on visual function for primary Sjögren's syndrome with dry eye. Forty-two eyes of 42 patients with primary Sjögren's syndrome were enrolled and were allocated randomly into artificial tears (AT) group and punctal plugs (PP) group. Ocular Surface Disease Index (OSDI) was used, and fluorescent staining for tear film break-up time (BUT), the Schirmer test I (STI) and contrast sensitivity was performed before treatment and was repeated 3 months after treatment. A follow-up of 3 months was achieved in 40 eyes of 40 patients, including 19 eyes in artificial tears group and 21 eyes in punctal plugs group. Statistically significant improvements were observed in the OSDI scores (AT: 52.6 ± 5.7, 15.9 ± 4.2; PP: 55.8 ± 4.9, 15.1 ± 4.2), corneal fluorescein staining scores (AT: 2.60 ± 1.76, 0.30 ± 0.57; PP: 1.91 ± 1.60, 0.09 ± 0.29), STI (AT: 3.85 ± 2.03, 8.95 ± 2.72; PP: 3.36 ± 1.62, 11.41 ± 2.65), and BUT (AT: 2.60 ± 1.39, 6.00 ± 1.81; PP: 2.27 ± 1.12, 7.82 ± 1.84) after treatment compared to those of pre-treatment. The values of STI (AT: 5.10 ± 1.80; PP: 8.05 ± 1.53) and BUT (AT: 3.40 ± 1.31; PP: 5.68 ± 1.13) in punctal plugs group were significantly more improved than those in the artificial tears group. The medium- and high-level frequencies contrast sensitivities were greatly improved in simulated daylight, night, and glare disability conditions after treatment with artificial tears and punctal plugs. However, the changes in contrast sensitivity did not significantly differ between groups. Both artificial tears and punctal plugs relieved dry eye symptoms, repaired corneal lesions, enhanced tear film stability, and improved contrast sensitivity. Punctal plugs could improve tear film stability and elongate the BUT better than artificial tears.

Functional and morphological changes in diabetic macular edema over the course of anti-vascular endothelial growth factor treatment

To evaluate macular morphology and function in diabetic macular edema (DME) over the course of intravitreal anti-vascular endothelial growth factor (VEGF) treatment with Ranibizumab. A consecutive series of 39 study eyes with centre-involving DME were included in this study. In all subjects, best-corrected visual acuity (BCVA) according ETDRS protocol, fluorescein angiography (FA), microperimetric macular sensitivity (MP) and Spectral Domain optical coherence tomography (SD-OCT) cross-sectional scans were obtained before treatment and after 3 monthly applied intravitreal Ranibizumab injections. Six different morphological qualities [IS/OS layer integrity, outer nuclear layer (ONL) cysts, ONL cyst size, inner nuclear layer (INL) cysts, blocking phenomenon and subretinal fluid] were graded of each cross-sectional OCT scan before and over the course of treatment by two experienced graders. Correlation analyses between functional and morphological parameters were obtained. Mean BCVA increased from 26 ± 14 to 33 ± 13 letters after 3 consecutive monthly applied Ranibizumab injections (p < 0.001). Central retinal thickness (CRT) decreased from 504 ± 144 to 387 ± 122 μm (p < 0.001). Over the course of treatment, IS/OS continuity improved (index: 0.56 ± 0.52 to 0.43 ± 0.49, Z = -1.415, p = 0.157), ONL cyst prevalence and size decreased significantly (index: 0.61 ± 0.44 to 0.56 ± 0.35, Z = -3.41, p = 0.001 and 1.75 ± 0.88 to 1.17 ± 1.05, Z = -4.02, p < 0.001), INL cyst prevalence decreased (index: 0.35 ± 0.52 to 0.28 ± 0.52, Z = -1.60, p = 0.109), blocking phenomenon did not change significantly (index: 00.12 ± 0.16 to 0.13 ± 0.15, Z = -0.45, p = 0.656) and subretinal fluid almost disappeared (index: 0.10 ± 0.24 vs. 0.00 ± 0.01, Z = -2.56, p = 0.011). Correlation analyses revealed highest significant correlations between ONL cyst prevalence and their size and CRT as well as BCVA and MP before treatment and over the course of treatment. ONL cysts and their size as morphological parameters correlate with retinal function measured with BCVA and microperimetry before and over the course of anti-VEGF therapy with Ranibizumab in patients with DME.

Long-term results of half-dose photodynamic therapy for chronic central serous chorioretinopathy with contrast sensitivity changes

To evaluate the efficacy and safety of photodynamic therapy (PDT) with half-dose verteporfin in patients with chronic central serous chorioretinopathy (CCSC) and retinal functional changes, by functional acuity contrast test (FACT). In this study, 27 eyes of 24 patients with CCSC were treated with PDT with half-dose verteporfin. Best-corrected visual acuity (BCVA), central foveal thickness (CFT) and resolution of subretinal fluid on optical coherence tomography (OCT), and leakage on fluorescein angiography (FA) and indocyanine green angiography (ICGA) were assessed. Contrast sensitivity test was performed at baseline and at 12th month for investigating retinal functional changes. The mean follow-up period was 25.33 ± 11.08 months. The mean age was 43.7 ± 8.6 years. Seventeen patients were male (70.8%) and seven patients were female (29.2%). Post PDT at 1st, 3rd, 6th, 12th month and at last follow-up, BCVA were significantly improved compared with the baseline BCVA (P<0.001), and CFT post PDT were significantly thinner than the baseline measurement (P<0.001). There was significant difference between pre- and post-PDT 12th month contrast sensitivities at all five different spatial frequency channels (P<0.01). Half-dose PDT is an effective and safe method in the treatment of CCSC with anatomical and functional success. The measurement of contrast sensitivity by FACT can be useful for evaluating the functional effectiveness of half-dose PDT for CCSC.

Detection of Diabetic Retinal Neuropathy Using Standard Clinical Electrodiagnostic Testing

Diabetes can lead to many systemic complications that include the nervous and renal systems. The vision of individuals with diabetes may be affected psychophysically, as noted with changes in dark adaptation, contrast sensitivity, glare recovery, color vision, and visual acuity. The primary ocular complication of diabetes is diabetic retinopathy-one of the leading causes of blindness in American adults.

Changes in visual function under mesopic and photopic conditions after intrastromal corneal ring segment implantation for different stages of keratoconus

To analyze and compare the changes in visual function under mesopic and photopic conditions in different stages of keratoconus before and after Keraring intrastromal corneal ring segment (ICRS) implantation. Clinico San Carlos Hospital and Faculty of Optics and Optometry, Complutense University, Madrid, Spain. Case series. Keratoconic eyes were evaluated under mesopic (0.1 to 0.2 candelas [cd]/m(2)) and photopic (85 cd/m(2)) conditions. LogMAR high-contrast corrected distance visual acuity (CDVA) and low-contrast CDVA were assessed using the Bailey-Lovie test and logarithmic contrast sensitivity, using the Pelli-Robson test. The study evaluated 12 eyes with stage I keratoconus, 21 eyes with stage 2, and 14 eyes with stage 3. The mean change in photopic high-contrast CDVA was 0.16 logMAR ± 0.20 (SD) (P<.00001). Photopic low-contrast CDVA increased by a mean of 0.14 ± 0.26 logMAR (P=.0005), photopic contrast sensitivity by a mean of 0.09 ± 0.22 logMAR (P=.005), and mesopic high-contrast CDVA by a mean of 0.10 ± 0.26 logMAR (P=.03). There were no significant differences between stages. Surgery did not affect the mean changes in mesopic low-contrast CDVA or mesopic contrast sensitivity for any stage. Implantation of ICRS in keratoconic eyes increased photopic high-contrast CDVA, low-contrast CDVA, and contrast sensitivity. Under low luminance, the mean changes in high-contrast CDVA, low-contrast CDVA, and contrast sensitivity did not worsen after ICRS implantation performed 5.0 mm from the visual axis, despite the rings being partially superimposed on the mydriatic pupil.

The changes of the contrast sensitivity after laser in situ keratomileusis for high myopia

Objective To investigate the early change of contrast sensitivity(CS) after laser in situ keratomilileusis (LASIK) under mesopic conditions for high myopia.Methods 66 cases (66 eyes) of high myopia were collected randomly to observe the changes of CS after the operation.Results 1 month postoperatively,mesopic CS decreased in low spatial frequencies (3 cycle/degree),medium spatial frequencies (6and 12 cycle/degree) and high spatial frequencies (18 cycle/degree).6 months postoperatively,low spatial frequencies of CS restored to the preoperative level,but medium and high spatial frequencies of CS could not restore to the preoperative level.All CS with glare were lower than CS without glare preoperatively and 1 month,3 months and 6 months postoperatively.Conclusion CS under mesopic conditions reduces after LASIK for high myopia.Only low spatial frequencies CS can restore to the preoperative level at 6 months postoperatively.Glare has influence on CS. Key words: Keratomileusis,laser in situ; Myopia,high; Contrast sensitivity

Simulating Images Seen by Patients with Inhomogeneous Sensitivity Losses

We aim to simulate how colored images are perceived by subjects with local achromatic and chromatic contrast sensitivity losses in the visual field (VF). The spatiochromatic corresponding pair algorithm, introduced in a previous article (J Opt Soc Am (A) 2004;21:176-186), has been implemented with a linear model of the visual system. Spatial information is processed separately by the chromatic and achromatic mechanisms by means of a multiscale model, with sensors selective to frequency, orientation, and spatial position, whose mechanism-dependent relative weights change with the spatial location of the image. These weights have been obtained from perimetric data from a patient with Leber's Hereditary Optic Neuropathy and an age-matched sample of normal subjects, using achromatic, red-green, and blue-yellow gratings of different spatial frequencies. Distortion contours for each mechanism have been derived from the images simulating the perception of these subjects at different locations in the VF. The images simulating the perception of normal subjects at different locations of the VF show a fast decrease in image quality with eccentricity. The same analysis carried out with the Leber's Hereditary Optic Neuropathy patient reveals worse overall image quality throughout the VF, plus a color vision defect resembling red-green dichromacy at fovea and trichromatic anomaly in the rest of the VF. In the present article, we show that implementing the algorithm with a spatial vision model that considers the changes in contrast sensitivity with spatial location of the stimulus may reveal the local effects that are suffered, in general, by pathological subjects, and that are ignored by simpler spatial vision models.