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PubMed1987

Contrast sensitivity and visual acuity of the pigmented rat determined electrophysiologically.

The contrast sensitivity function of the rat was assessed by investigating the relationship between the amplitude of visually evoked cortical potentials (VECP) and the spatial frequency and contrast of grating stimuli. Pattern reversal VECPs were recorded in Area 17 in the region of representation of the central binocular visual field. Transient responses were obtained with a 1 Hz contrast reversal. The mean contralateral monocular CSF peaked around 0.1 c/deg, with a threshold sensitivity of 20-25, low frequency attenuation and a high frequency cut-off of 1.18 c/deg. The mean binocular CSF showed a cut-off of 1.20 c/deg, which matches several behavioural measurements of visual acuity. The greater binocular sensitivity in the low frequency range (0.04 c/deg) could be tentatively attributed to the greater influence of the population of large ganglion cells that reaches its maximal density in the ipsilateral projection.

Animals↗
PubMed1998

Relationships among visual acuity demands, convergence, and nystagmus in patients with manifest/latent nystagmus.

BACKGROUND: We investigated the role convergence plays in nystagmus dampening, in particular, relationships among visual acuity demands, convergence, and nystagmus. Previously we showed that subjects with idiopathic infantile nystagmus exhibit a range of responses to acuity targets, one of which is nystagmus blockage syndrome. We report herein eye movement responses to acuity targets of patients with manifest/latent nystagmus. METHODS: Fourteen patients, 11 with latent or manifest latent nystagmus and 3 with combined manifest latent with infantile nystagmus, were asked to indicate the direction of the gap in Landolt C optotypes while their eye movements were recorded. RESULTS: The tested patients exhibited various responses to acuity demands: (1) dampening of nystagmus with convergence (i.e., nystagmus blockage syndrome) (5/14 patients), (2) changes in vergence without nystagmus dampening (2 patients), (3) decrease of nystagmus without convergence (2 patients), and (4) little change in nystagmus or vergence (5 patients). In nystagmus blockage syndrome the amount of convergence increased with acuity demands in two of five patients and the convergence duration in four of five patients; nystagmus dampening increased with acuity demands in one of five patients and the blockage duration in four of five patients. CONCLUSIONS: Many, but not all, patients with manifest/latent nystagmus, similar to those with infantile nystagmus, used convergence to dampen their nystagmus. The convergence response tended to increase with acuity demands, but the amount of dampening was idiosyncratic and not predictably related to the measured convergence across patients.

Adolescent↗
PubMed2006

Defining myopia using refractive error and uncorrected logMAR visual acuity >0.3 from 1334 Singapore school children ages 7-9 years.

AIM: To determine the association of spherical equivalent (SE) with low uncorrected visual acuity (VA) along with a proposed definition for myopia using logMAR VA >0.3 as the criteria. METHODS: 1334 Chinese schoolchildren (mean age 7.8; range 7-9 years) were enrolled in the study after those who had hyperopia > or =+2.00 dioptres (D) and astigmatism > = -2.00 D were excluded. Uncorrected logMAR VA was measured for both eyes. Cycloplegia autorefraction was achieved by the instillation of three drops of 1% cyclopentolate 5 minutes apart. The average of five successful consecutive refraction and keratometry readings were obtained with calibrated Canon RK5 autokeratorefractometers by well trained optometry students, at least 30 minutes after the instillation of the third drop of cyclopentolate. SE cut-off points (-0.25 D, -0.5D, -0.75 D, -1.0 D) were evaluated. RESULTS: Using different SE cut-off points, the myopia prevalence rates of this sample of schoolchildren varied from 45.8% (SE at least -0.25 D) to 30.7% (SE at least -1.0 D). The cut-off point of > or =-0.75 D had a sensitivity and specificity of 91.8% (95% CI, 89.2 to 94.4) and 93.7% (95% CI, 92.1 to 95.3), respectively, to predict low vision defined as uncorrected logMAR VA > 0.3 (either eye). The next best cut-off point of -0.5D had a higher sensitivity (93.3%), but lower specificity (87.9%). CONCLUSIONS: The cut-off points of -0.75D and -0.5D in SE refraction are appropriate for the prediction of uncorrected logMAR VA worse than 0.3, which is the criterion for the US common state adult driver licensing standard.

Child↗
PubMed1979

Heterogeneity of failure of visual acuity in Graves' disease.

The eye manifestations of Graves' disease are usually mild and self-limiting. Occasionally they follow a progressive course leading to visual loss and total blindness. The ocular manifestations bear no relationship to the metabolic state and may appear before, during or after onset of thyrotoxicosis. Characteristically they become evident at about the time of onset of hypermetabolism. Various factors responsible for the failure of visual acuity are discussed with case illustrations.

Adult↗
PubMed1982

[Fixation in cases of reduced visual acuity (author's transl)].

The authors describe a new device wih a built-in fixation lamp, which enables small children and patients with reduced visual acuity to fix more steadily. The device generates a sequence of flashes for fixation without any risk of triggering photoconvulsive responses.

Adult↗
PubMed2002

Posttreatment visual acuity in patients treated with episcleral plaque therapy for choroidal melanomas: dose and dose rate effects.

PURPOSE: To determine the relationship between the long-term visual function and the dose and dose rates delivered to critical ocular structures in patients with choroidal melanoma treated with 125I episcleral plaque radiotherapy. MATERIALS AND METHODS: From 1987 to 1994, 63 patients underwent 125I episcleral plaque (Collaborative Ocular Melanoma Study [COMS] design) application for the treatment of choroidal melanoma. The mean tumor height was 4.5 mm (range 1.7-8.3). Doses and dose rates at the tumor apex, macula, and optic disc were calculated. Forty-three records were scored to assess whether a decrease in visual acuity of >2 lines on a standard Snellen eye chart had occurred. Patient age and the presence of hypertension or diabetes were noted. Statistical analysis was performed to assess both the rate at which visual decline had occurred and the presence of significant factors that had contributed to this decline. RESULTS: With a median follow-up of 36 months, the 3-year actuarial survival rate was 93.6%. The 3-year actuarial local control rate was 86.9%. The median time to visual loss after therapy was 18.7 months. The 3-year actuarial rate of visual preservation was 40.5%. Multivariate analysis demonstrated higher macula dose rates (p = 0.003) to forecast visual decline. Macula dose rates of 111 +/- 11.1 cGy/h were associated with a 50% risk of significant visual loss. CONCLUSION: Patients in our series treated with 125I plaque brachytherapy for choroidal melanoma experienced favorable tumor control, but with a measurable incidence of visual decline. Higher dose rates to the macula correlated strongly with poorer posttreatment visual outcome. This information may be valuable in selecting the optimal dose rates to treat choroidal melanomas and to predict the risk of visual decline.

Adult↗
PubMed1987

Biofeedback training of visual acuity and myopia: a pilot study.

Biofeedback training of accommodation was performed with nine subjects using the Accommotrac Vision Trainer to attempt to improve visual acuity (VA) and reduce myopia. A single-subject research design was used. Improvements in VA were seen with some subjects, but it is not clear whether the improvements were due to the biofeedback training alone, or to a learning effect observed during repeated measurements of VA. There was no change in refractive error. Implications for future research are discussed.

Accommodation, Ocular↗
PubMedDate not supplied

Visual acuity and binocularity in children with unilateral acquired aphakia.

Seventeen cases of unilateral aphakia secondary to acquired cataracts and dislocated lenses were presented. Final visual acuity was 20/70 or better in 12 of our 17 patients. Binocular single vision has been maintained in four cases. Ten patients had a posttherapy tropia. Early surgery and treatment particularly in the young child is stressed in order to maintain normal binocular single vision. Where once traumatized eyes were felt to be "sick" eyes and better left alone, current surgical and therapeutic methods make restoration of vision and binocularity a reasonable goal.

Adolescent↗
PubMed2003

Visual acuity, amblyopia, and ocular pathology in 12- to 13-year-old children in Northern Mexico.

PURPOSE: The aim of this study was to establish visual acuity (VA) and the prevalence of amblyopia and other ocular disorders in a population of 12- to 13-year-old children in Mexico who have not been vision screened. METHODS: A total of 1,035 12- to 13-year-old children were examined in a field study. The examination included VA, stereopsis, cover testing, refractive retinoscopy, and examination of the red reflex and posterior pole. In cases with unexplained subnormal VA, visually evoked potential/visually evoked response was also performed. RESULTS: A >or=20/20 in at least one eye was found in 93% of the subjects. Bilateral VA <or=20/40 was found in 0.3% of cases. None of the subjects had bilateral VA <20/60. Amblyopia (<or=20/40) was found in 26 subjects (2.5%). In 10 cases, the cause of subnormal VA was unexplained. Ocular albinism was found in 3 cases, whereas strabismus was found in 24 subjects (2.3%). There were very few ocular opacities or posterior pole abnormalities. CONCLUSIONS: The visual status in the Mexican 12- to 13-year-old children tested was good. The prevalence of amblyopia was similar to that in other unscreened populations.

Adolescent↗
PubMed1995

Visual acuity changes throughout adulthood in normal, healthy eyes: seeing beyond 6/6.

There are many useful longitudinal and cross-sectional epidemiological studies of how visual acuity (VA) deteriorates with age. However, few studies have evaluated age-related VA changes in normal, healthy eyes. Data from three previous studies that included VA measurements taken with logMAR charts from subjects with normal, healthy eyes were collated and additional data from 42 subjects were added. This provided VA results from 223 subjects (age range 18 to 80 years). Mean logMAR VA improved from -0.13 (Snellen equivalent 6/4.5) in 18- to 24-year-olds to -0.16 (Snellen 6/4(-1)) in 25- to 29-year-olds and then gradually became worse with age to a mean value of -0.02 (Snellen 6/6+1) for subjects over 75 years of age. The inadequacy of 6/6 as a norm value of VA is illustrated. The data show VA levels far superior to the data from the standard references of Pitts (1982) and Weale. (1975, 82) We suggest that this is because we used logMAR charts (providing nontruncated data), the subject's optimal refractive correction (rather than habitual) and strict exclusion criteria ensuring that only subjects with normal, healthy eyes were recruited for the studies.

Adolescent↗
PubMed1990

Explanation for good visual acuity in uncorrected residual hyperopia and presbyopia after radial keratotomy.

It has been observed that, after radial keratotomy (RK), uncorrected residual hyperopes may have better visual acuity than expected and that some presbyopes, corrected only for distance, have adequate near-vision. We offer a possible explanation for these observations by showing that the increased spherical aberration after RK may produce a second focus 1.5 diopters or more in front of the principal focus of the eye.

Contrast Sensitivity↗
PubMed2004

Preschool visual acuity screening with HOTV and Lea symbols: testability and between-test agreement.

PURPOSE: To compare the performance of 3- to 5-year-old children on visual acuity screening with HOTV letters vs. Lea symbols as optotypes. METHODS: Subjects included 1253 Head Start children who were aged either 3 or 4 years on September 1 of the school year of testing. The sample over-represented children who had not passed a Head Start screening. Binocular pretesting at 1 m demonstrated the child's ability to identify the optotypes verbally or by matching optotypes on a lap card. Acuity was tested monocularly at 3 m using crowded single lines of optotypes. Lines tested were based on age at the beginning of the school year (September 1) with 3-year-old children tested with lines 10/100, 10/32, 10/25, and 10/20 and 4-year-old children tested with 10/100, 10/25, 10/20, and 10/16. RESULTS: Overall, 99% of children were able to complete the binocular pretest for each test successfully, and there was no difference between the tests (p = 0.83). Children's ability to complete the pretest increased slightly with age. HOTV test scores were slightly worse than Lea symbols test scores (p = 0.047), primarily because more children were unable to pass the monocular 10/100 card for the HOTV test than for the Lea symbols test (2.6% vs. 1.3%). The percentage of identical results on HOTV vs. Lea overall was 67.3% and increased significantly with age. When the results were different, 3-year-old children, but not 4- and 5-year-old children, tended to have worse results on the HOTV letter test. CONCLUSIONS: The vision of nearly all 3- to 5-year-old children can be screened using either HOTV letters or Lea symbols. HOTV letters may be slightly more difficult than Lea symbols for 3- to 5-year-old children, with the largest difference between acuity results on the two tests occurring in 3-year-old children.

Aging↗
PubMed1990

Corneal topography of patients with excellent Snellen visual acuity after epikeratophakia for aphakia.

A computer-based corneal topographic analysis system was used to evaluate the patterns of power distribution in five patients with at least six months of postoperative follow-up who obtained excellent visual and refractive results after epikeratophakia for aphakia. All grafts were well centered relative to the visual axis. The range of surface power seen within the central 5 mm of the individual grafts ranged from 4.00 to 6.50 diopters. Each graft showed a unique, moderately irregular pattern of power distribution. Fair correlation was seen between the expected corneal power and that shown in the power map displays. These data suggest that moderate degrees of irregular astigmatism are compatible with good Snellen visual acuity after epikeratophakia for aphakia, though the effect of this irregularity on visual performance remains unclear.

Aged↗
PubMed2003

Effect of photorefractive keratectomy and laser in situ keratomileusis in high myopia on logMAR visual acuity and contrast sensitivity.

PURPOSE: To compare effect of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) on contrast sensitivity (CS) and best corrected visual acuity (BCVA) in high myopia. METHODS: 38 myopes (PRK) and 31 patients (LASIK) were examined before and 1, 3, 6, and 12 months postoperatively. Mean preoperative spherical equivalent was -8.0 +/- 1.7D (PRK) and -9.2 +/- 2.1D (LASIK). CS was tested on a computerized system of the Contrast Sensitivity 8010 Type at 6 spatial frequencies (0.74 and 29.55 c/deg), BCVA was measured on logMAR charts. RESULTS: At 12 months postoperatively, mean spherical equivalent was -0.6 +/- 1.0D (PRK) and -1.0 +/- 0.8D (LASIK). Postoperative values of CS were significantly higher in the PRK group, except for spatial frequencies of 3.69 and 7.39 c/deg up to 3 months postoperatively. The initial significant decrease of BCVA lasted up to 6 months after PRK. In the LASIK group BCVA was not significantly different from its preoperative level at the 3-months follow-up. CONCLUSIONS: The significant improvement of CS after PRK suggest that PRK can improve quality of vision in eyes with high myopia. Although recovery of BCVA after LASIK was faster than after PRK, there may be a persistent decrease in CS.

Contrast Sensitivity↗
PubMed2005

Correlation of optical coherence tomography findings with visual acuity and macular lesions in patients with X-linked retinoschisis.

PURPOSE: To evaluate and correlate findings obtained by optical coherence tomography (OCT) imaging with visual acuity (VA) and macular lesions in patients with X-linked retinoschisis (XLRS). DESIGN: Prospective comparative case series. PARTICIPANTS: Thirty-one patients with confirmed XLRS. METHODS: Best-corrected VA was determined using Early Treatment Diabetic Retinopathy Study charts, and a dilated funduscopic examination was performed on all patients. For all patients, the macula in each eye was OCT imaged. A correlation between VA, macular presentation, and OCT images was determined. MAIN OUTCOME MEASURES: Analysis of findings on OCT images, including foveal thickness and the area of macular cystic-appearing lesions, and their correlation with VA. RESULTS: Twenty-five patients with funduscopically evident cystic-appearing macular lesions demonstrated cysticlike spaces on OCT images. No statistically significant correlation was observed between the macular area of the cysticlike spaces, foveal thickness, and VA. Three patients with no funduscopic or OCT evidence of foveal cysts demonstrated thinning of the fovea on OCT images and more extensive reduction of their VA. Retinal papillomacular bundle nerve fiber layer thickness on OCT images showed no significant difference between control and patient groups. CONCLUSIONS: In XLRS patients with cystic-appearing macular lesions, there was a lack of correlation between VA, foveal thickness, and cystic area. The anatomical appearance of smaller perifoveal cysts on OCT imaging was most consistent with their location being primarily within the inner nuclear layer of the retina. In older patients, macular cysts were no longer apparent clinically or by OCT imaging, and foveal thickness was reduced. The findings on OCT images are consistent with the hypothesis of a primary Muller cell defect in patients with XLRS.

Adolescent↗