Visual acuity in the newborn with notes on some objective methods to determine visual acuity.
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Methods of visual acuity determination with the spatial frequency sweep visual evoked potential.
PURPOSE: The spatial frequency sweep visual evoked potential (sVEP) is used to rapidly determine visual acuity in children or non-responsive patients. Two techniques have been used to separate signal from noise: (1) the 95% confidence interval for the signal amplitude (95% CI) or (2) the amplitude of a Fourier frequency adjacent to 2x the signal frequency (DFT). The purpose of this study is to determine if there is a significant difference in acuity estimates with these techniques. METHODS: Ten normal subjects (approximately 0.00 logMAR acuity) and 11 patients with decreased visual acuity took part in this project. Stimulus production and data analysis were done with an Enfant 4010 (Neuroscientific Corp). Standard VEP recording techniques were employed. The stimulus was a horizontal-oriented, sine wave grating that swept up the spatial frequency spectrum (contrast 80%, temporal reversal rate 7.5 Hz). Sweeps were repeated until the confidence intervals for the data were no longer decreasing. The Bailey Lovie logMAR chart was used to determine visual acuity. A line was fit to the high spatial frequency data using either the 95% CI or the DFT as the noise estimate. By using these linear equations, acuity estimates were obtained at 0, 1, and 2 microV signal amplitudes. RESULTS: The average logMAR acuity for the subjects with normal acuity was -0.06 +/- 0.070 (SD). The sVEP acuity estimates were 0.08 +/- 0.098, 0.18 +/- 0.092, and 0.33 +/- 0.195 (0, 1, and 2 microV extrapolations) with the 95% CI used as noise and 0.07 +/- 0.100, 0.18 +/- 0.103, and 0.33 +/- 0.202 (0, 1, and 2 microV extrapolations) with the DFT used as noise. By using the average noise from the Fourier frequency as the extrapolation level, the acuity was 0.10 +/- 0.098 logMAR. The average logMAR acuity for the subjects with decreased visual acuity was 0.67 +/- 0.306 (SD). The sVEP acuity estimates were 0.53 +/- 0.175, 0.66 +/- 0.171, and 0.88 +/- 0.295 (0, 1, and 2 microV extrapolations) with the 95% CI used as noise and 0.53 +/- 0.179, 0.65 +/- 0.176, and 0.86 +/- 0.268 (0, 1, and 2 microV extrapolations) with the DFT used as noise. By using the average noise from the Fourier frequency as the extrapolation level, the acuity was 0.57 +/- 0.186 logMAR. No significant difference was found between the two acuity estimate techniques for all of the subjects (repeated measures ANOVA, p = 0.16, F20 = 2.131). The sVEP estimates of acuity to the 0 microV and noise levels were not significantly different from the logMAR acuity (paired t-test, all p values > 0.05). CONCLUSIONS: The results indicate that the sVEP acuity does not depend on the noise estimation technique. In agreement with prior studies, the sVEP acuity underestimates the logMAR acuity in normally sighted individuals by about an octave.
Adolescent↗
Bioptic telescopes meet the needs of drivers with moderate visual acuity loss.
PURPOSE: Visually impaired people are permitted to use bioptic telescopes for driving in many states in the United States. However, it has been suggested that the telescope is used only to meet the visual acuity criteria for licensure. In this study, a survey was used to establish the extent to which bioptic telescopes are used by and meet the driving needs of people with moderately reduced visual acuity. METHODS: A cross-sectional survey of a convenience sample of 58 bioptic drivers was administered by telephone interview. Bioptic telescope usage patterns were quantified with questions designed specifically for the study. Driving patterns were quantified by use of the Driving Habits Questionnaire. Subjects were recruited from four sources across the United States to ensure a range of bioptic training and driving experience. RESULTS: The majority (74%) rated the bioptic telescope as very helpful, and almost all (90%) would continue to use it for driving, even if it were not required for driving licensure; however, only 62% reported always wearing the bioptic when driving. Subjects had relatively unrestricted driving habits, driving a mean of 222 +/- 211 miles per week, and 85% aged < or =65 years drove to work. With the exception of driving in rain, in bright sunlight, and at night, there was little difficulty with driving in a variety of situations, and levels of driving avoidance due to vision impairment were low (<10%). CONCLUSIONS: The bioptic telescope met the (self-reported) driving needs of the majority of visually impaired drivers in this survey and was found to be a useful aid for tasks requiring resolution of detail.
Adolescent↗
Vitrectomy for epiretinal membranes with good visual acuity.
PURPOSE: To evaluate the visual results of vitrectomy for epiretinal membrane in eyes with a preoperative visual acuity of 20/50 or better. METHODS: The visual results and complications were analyzed following vitrectomy for idiopathic epiretinal membranes and epiretinal membranes secondary to retinal tears. This study was a retrospective, consecutive case series of 40 eyes of 40 patients treated by a single surgeon. RESULTS: The mean preoperative visual acuity was 20/50 +2 (range, 20/30 +1 to 20/50 -3). The mean visual acuity improved to 20/40 +2 (P = .02) by the final examination at a mean of 2.4 years following surgery. The status of the lens at the final examination was correlated with the visual results of surgery. Twenty-one eyes were phakic preoperatively, and 14 of these eyes had cataracts removed by the final examination. The mean preoperative visual acuity in seven eyes that were still phakic at the final examination was 20/50, and this decreased to 20/50 -2 (P = .82). The mean preoperative visual acuity was 20/50 +2 in 33 eyes that were pseudophakic by the final examination, and this improved to 20/32 -2 (P = .005). The visual acuity improved by 2 or more Snellen lines in only one in seven eyes (14%) that were still phakic on the final examination and in 14 of 33 eyes (42.4%) that were pseudophakic by the final examination. There were no serious surgical complications. CONCLUSIONS: Vitrectomy for epiretinal membranes is beneficial in eyes with relatively good preoperative visual acuities, but cataract surgery is necessary in phakic eyes to achieve long-term visual acuity improvement.
Aged↗
[Predicting visual acuity in media opacities and uncorrectable refractive errors. Assessing so-called "retinal visual acuity"].
Three different components contribute to the modulation transfer function of the visual system: (1) formation of the optical image (refractive media, pupil); (2) scattering of light in the prereceptoral layers of the retina; (3) neuronal processing in the retina und superior visual centers. In the presence of media opacities or non-correctable refractive errors, the clinical question often arises as to which macular function can be expected under the assumption of normal optical image formation (e.g. prior to cataract extraction, corneal transplantation, or vitrectomy). Simple tests such as light projection, color discrimination, and two-point discrimination cannot provide adequate information about macular function. The same holds true for the global luminance ERG. The X-ray phosphene is obsolete. The Maddox rod (with limitations), transilluminated Amsler grid, and various entoptic phenomena (Purkinje vascular phenomenon, foveal chagrin, Haidinger's brushes, blue field phenomenon) are available as qualitative subjective tests. Maxwellian view systems with pinhole aperture (potential acuity meter PAM) and the interferometers (retinometer, visometer, SITE-IRAS interferometer) provide quantitative subjective methods. The flash VECP is primarily a qualitative objective test that allows semiquantitative acuity prediction under special conditions (unilateral opacities). Psychophysical criteria that are less affected by the quality of the retinal image show promising developments in future subjective tests, e.g. optotypes in positive contrast, optotypes or targets superimposed on a background of optical noise, or hyperacuity. Future objective test developments are pattern VECP or even pattern ERG elicited by interferometric stimulation, speckle VECP and focal ERG.
Cataract↗
[The influrence of visual acuity and contrast sensitivity on subjective evaluation of visual function before and after cataract surgery].
PURPOSE: To assess the influence of visual acuity and contrast sensitivity on subjective evaluation of visual function investigated by means of questionnaires in patients before and after cataract surgery. METHODS: Visual acuity was tested on Snellen projection optotypes and logMAR optotype chart with Landolt rings, contrast sensitivity was tested on Pelli-Robson chart. The questionnaire included Visual Functioning Index VF-14, Cataract Symptom Score and Global Measures of Vision--self-reported trouble and satisfaction with vision. 37 cataract patients were examined, including completing the questionnaire, 1 day before and 7 weeks after the surgery. RESULTS: Most patients (65%) suffer from moderate troubles with their vision and are moderately dissatisfied (51%) before cataract surgery. After the surgery, a majority of patients have no troubles (51%) and are very satisfied (54%). Visual acuity (VA) correlates only with VF-14, namely only VA of non-operated eye (p < 0.01), binocular VA before (p < 0.001) and after surgery (p < 0.05). Contrast sensitivity (of non-operated eye, operated eye, binocular) correlates with more subjective parameters (VF-14, self-reported trouble and satisfaction with vision), namely both before and after the surgery (p < 0.05, p < 0.01, p < 0.001). CONCLUSION: After cataract surgery, visual acuity, contrast sensitivity and subjective parameters of visual functions significantly improve. Subjective parameters correlate more with contrast sensitivity then with visual acuity. Contrast sensitivity is more related than visual acuity to real world in patients with cataract.
Aged↗
[A simple method of assessing monocular visual acuity in nystagmus ].
Visual acuity examined with both eyes-binocularly-often shows a better result than monocular examination. The nystagmus intensity increases when one eye is occluded or vision is blurred by a plus lens. The authors suggest a simple method to examine visual acuity monocularly. The procedure is appropriate to preserve the attenuation of nystagmus under binocular condition.
Humans↗
The relationship between visual acuity, pupillary defect, and visual field loss.
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Eye Diseases↗
[Low visual acuity, disorders of the visual field: how to adapt the imaging of optical pathways to clinical practice?].
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Diagnostic Imaging↗
[Dynamics of visual functions in the conditions of glow and sodium lighting. I. Visual acuity, accommodation, flicker fusion, visual field and heterophoria].
Investigations of the functions cited in the title were performed in 23 persons with a normal visual system in conditions of equal illumination, first the glow and the next day or later--the sodium one. All the tests were carried out three times in the morning hours evaluating in this way their dynamics as the time goes. The authors are analyzing the degree of the variability of the discussed functions in the time, as well as their behaviour in conditions of applied illumination. The results obtained suggest that in conditions of illumination by a high-pressure sodium lamp no negative characteristics of this source of light emerged. Deterioration of a small degree was observed only in the range of accommodation for near.
Accommodation, Ocular↗
[Studies on the kinetic visual acuity; on the influence of flickering light upon the kinetic visual acuity].
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Adult↗
[Physiological basis of visual acuity measurement].
The paper presents information about types of acuity tasks, visual acuity limitations and contrast sensitivity function. Measurements of resolution acuity may be interpreted as estimates of spatial density of the mosaic of photoreceptors and ganglion cells of the living human eye. Physiological basis such as Raleigh's criteria, sampling theory and filtering theory of visual resolution are described.
Form Perception↗
Potential acuity meter versus scanning laser ophthalmoscope to predict visual acuity in cataract patients.
PURPOSE: To compare the relative abilities of the Potential Acuity Meter (PAM) and the Scanning Laser Ophthalmoscope (SLO) to predict the postoperative visual acuity in patients with mild to dense cataract. SETTING: Gimbel Eye Centre, Calgary, Alberta, Canada. METHODS: In this single-masked prospective study of 31 consecutive eyes with mild to dense cataract and a best corrected visual acuity (BCVA) of 20/40 or less, patients had predictive visual acuity (PVA) testing using the PAM and SLO. Preoperative and postoperative BCVA was recorded using Snellen charts. Differences between PVA and postoperative BCVA results were assessed by a two-tailed t-test and correlation analysis. RESULTS: The SLO was correct within two lines of outcome in 30 of 31 eyes and the PAM, in 19 of 31 eyes. A two-tailed dependent t-test showed a significant difference between predicted and final visual acuity for the PAM (P = .0001) and a nonsignificant difference for the predicted and final visual acuity for the SLO. A correlation analysis showed a mild correlation for the PAM (r = .49) and a good correlation for the SLO (r = .81). For a prediction of better or worse than 20/40, the SLO showed a sensitivity of 0.964 and specificity of 1.0 and the PAM, of 0.67 and 1.0, respectively. CONCLUSION: The SLO was more accurate than the PAM in predicting visual acuity after cataract surgery. The relative cost of the SLO is potentially restrictive to its widespread clinical application. However, the cost/benefit in terms of patient satisfaction with predictable surgical results should be considered.
Aged↗
Relationship between visual acuity and observation distance.
The visual acuities of 17 young emmetropes and corrected ametropes were measured over the range of 7.5-0.19 m using a Bailey-Lovie chart. Accommodation stimulus-response measures were also taken over this range using retinoscopy to establish whether variations in visual acuity with observation distance could be attributed to accommodation behaviour. Tonic accommodation was recorded using the Canon R1 autorefractor and was compared with visual acuity and stimulus-response results. In general, visual acuity was found to be dependent on stimulus distance, being significantly reduced for most observers for the closest targets. There were three categories of observer performance for visual acuity as a function of observation distance; one group showing no change in visual acuity with distance, a second showing a flat function for distances 7.55-0.5 m, and then a decrease in visual acuity for shorter distances; and a third category that showed a maximum visual acuity in the 1.2-1.6 m region. This behaviour was unrelated to individual stimulus-response characteristics and there was no significant relationship between tonic accommodation and the distance where acuity was best for the third category observers.
Accommodation, Ocular↗
Grating-acuity in children. Normal values of visual acuity in children up to 13 years as assessed by the acuity card procedure.
The acuity card procedure proved to be a useful method for assessing visual acuity in children. Normal values of visual acuity measured by this method had already been assessed in children up to four years. To enable application of the test in older children this study obtained values in a group of 396 normal children, aged three months to 13 years. The mean curve as well as the 10th centile was calculated in different age groups. A considerable variation of acuity values causing a 'dip' in the 10th centile was found in the ages 18 to 24 months. A smaller 'dip' was found in the ages 48 to 52 months. This has to be attributed to behavioural properties connected with age. The results obtained in the group of children under four years of age corresponded fairly well with other studies. In schoolchildren a fair agreement could also be found between the data obtained using the acuity card procedure and the data obtained with the Landolt-C rings. Obtaining normal values for the acuity card procedure in children covering a wide age range facilitates recognition of visual handicap in children who are difficult to assess.
Adolescent↗
Effect of mental retardation and motor disability on testing with visual acuity cards.
The visual acuity of 77 children (aged between 1 1/2 and eight years) with cerebral palsy and mental retardation was tested using acuity cards. Results varied by no more than one octave in 79 per cent of the cases. The median acuity of children with severe motor disabilities was lower and the variability from test to test was greater than for those with mild motor disabilities. Grouping the children roughly according to degree of mental retardation, the more retarded group tended to be more visually disabled and vary more from test to test. In general, day-to-day variability was greater than within-day inter-observer variability. The use of acuity cards to evaluate visual acuity in severely disabled and mentally retarded children, whose acuity is difficult to evaluate with conventional acuity tests, is a useful alternative method.
Adolescent↗
Fresnel prisms and their effects on visual acuity and binocularity.
1. The visual acuity with the Fresnel membrane prism is significantly less than that with the conventional prism of the same power for all prism powers from 12 delta through 30 delata at distance and from 15 delta through 30 delta at near. 2. The difference in the visual acuity between base up and base down, and between base in and base out, is not significantly different for either the Fresnel membrane prism or for the conventional prism. 3. For both Fresnel membrane prism and the conventional prism, the visual acuity when looking straight ahead. 4. Using Fresnel membrane prisms of the same power from different lots, the visual acuity varied significantly. The 30 delta prism caused the widest range in visual acuity. 5. When normal subjects are fitted with the higher powers of the Fresnel membrane prism, fusion and stereopsis are disrupted to such an extent that the use of this device to restore or to improve binocular vision in cases with large-angle deviations is seriously questioned. 6. Moreover, the disruption of fusion and stereopsis is abrupt and severe and does not parallel the decrease in visual acuity. The severely reduced ability to maintain fusion may be related to the optical aberrations, which, in turn, may be due to the molding process and the polyvinyl chloride molding material. 7. Through the flexibility of the membrane prism is a definite advantage, because of its proclivity to reduce visual acuity and increase aberrations its prescription for adults often must be limited to only one eye. 8. For the same reasons in the young child with binocular vision problems, the membrane prism presently available should be prescribed over both eyes only in powers less than 20 delta. When the membrane prism is to be used as a partial occluder (over one eye only), any power can be used. 9. The new Fresnel "hard" prism reduces visual acuity minimally and rarely disrupts binocularity, thus increasing the potential for prismotherapy to establish binocularity. This prism is currently available only for use as a trial set. Since the cosmetic appearance of the Fresnel "hard" prism is similar to that of the Fresnel membrane prism and it is easier to maintain, it would be the prism of choice (over all other types) for bilateral prescriptions in the young patient with emmetropia. The manufacturer is urged to make these prisms available to fit a special round adjustable frame, such as that developed in Europe for use with the wafer prism.
Adolescent↗
The development of visual acuity in the peripheral visual field of human infants: binocular and monocular measurements.
We measured binocular and monocular grating acuity in the peripheral visual field of infants, using a modified preferential looking procedure. Both binocular and monocular peripheral acuity increased between 2 and 11 months of age, but had not reached adult levels at the end of the first year of life. Binocular acuity was always higher than monocular acuity. At all ages tested, acuity was higher in the temporal than in the nasal visual field. We conclude that, in spite of the relative morphological maturity of the peripheral retina, visual acuity develops in the peripheral visual field.
Adult↗