The Visual Hand Display: A Focus on Collaboration

When young children experience subnormal vision, an array of evaluation tools and techniques is used to assess visual function. Some children who have retinopathy of prematurity may require surgery. Post-operatively, at the Children's Low Vision Center in Boston, the pediatric ophthalmologist evaluates the child's visual functioning using a variety of devices. A tool called the Visual Hand Display has been introduced to enhance the physician's methods of evaluation, thereby achieving greater understanding of the child's visual responses. Collaborations among the doctors, educators, therapists, and patients are emphasized.

Congenital Combined Deficiency of Factor V and Factor VIII

A case of congenital combined deficiency of factor V and factor VIII was reported. The patient, a 9 year old boy, gave a history of epistaxis, hematomas, and of hemorrhages following dental extraction since the age of 2 ; plasma levels of factor V and factor VIII were found to be 16% and 8% of normal, respectively. No one in his family had a deficiency of either factor. The effects of transfusion of normal fresh plasma and whole blood from a patient with hemophilia A were studied. While the former were similar to the pattern as seen in classical hemophilia, the latter consisted of an immediate increase of factor V activity and a delayed increase of factor VIII activity, despite the fact that factor VIII activity was almost absent from the donor’s blood.

Neurovisual abnormalities preceding the retinopathy in patients with long-term type 1 diabetes mellitus

BACKGROUND

Changes in the retina caused by diabetes may lead to visual impairment in dim light, even with good visual acuity and visual fields. To evaluate the visual abnormalities preceding the retinopathy in patients with type 1 diabetes mellitus (DM), we applied electrophysiological methods.

METHODS

The visual evoked responses were recorded with sinusoidally modulated vertical gratings at 10 spatial frequencies presented sequentially on a high-resolution monitor in patients with type 1 DM and in normal volunteers. Similarly, the contrast visual evoked responses of 10 contrast levels were recorded at five spatial frequencies. Both amplitudes at the second harmonic were calculated by discrete Fourier transform. The visual acuity and contrast thresholds were determined objectively.

RESULTS

There was dissociation between the Snellen and the estimated visual evoked response acuity measurements in patients with diabetes (r2=0.077, P=0.44). The saturation phenomena were observed at lower levels of contrast stimuli than in normal individuals at. 1.0, 2.0, 4.0 and 8.0 cycles per degree (P=0.0001). The contrast sensitivity function was deeply abnormal in all tested patients despite the metabolic control. The values of the area under the curve of the visual evoked response amplitude-contrast level function at five spatial frequencies were smaller in patients with DM than in the control group (P<0.05) at all spatial frequencies tested.

CONCLUSIONS

Patients with type 1 DM without retinopathy showed significant lower amplitude of the visual evoked responses at all spatial frequencies tested, with the saturation phenomena observed at lower level of contrast stimuli. In addition, there was a dissociation between the sweep visual evoked responses and the Snellen acuity measurements. A significant and nonselective neuronal visual loss involving the visual pathway precedes the ophthalmoscopically detectable retinopathy in patients with type 1 DM.

Visual Ability Score -- a new method to analyze ability in visually impaired children

PURPOSE

We analyzed the correlation between the Preferential Looking (PL) acuities and the Visual Ability Scores (VAS) of 600 patients (many with severe retinopathy of prematurity) to determine their ability to perform various activities within the daily environment.

METHODS

Visual acuity was measured by PL. Sixteen visual activities within the environment were analyzed. The VAS (range, 1-16) were calculated from the results of each activity and correlated with PL acuity.

RESULTS

The PL acuities of the 600 patients ranged from 20/20 (1.0) to <20/3200 (0.006) [mean, 20/337(006)]. The VAS ranged from 1 to 16 points (mean, 10.65; SD, +/-4.80) and showed a high correlation with the PL acuities (r=0.917, p=0.0001).

CONCLUSIONS

In addition to PL vision testing, analyzing the environmental visual behavior of young, severely visually impaired patients is important to accurately evaluate visual abilities. We found the VAS to be an important aid for low-vision specialists, especially for those with no access to a vision evaluation system such as PL.

Objective measurement of contrast sensitivity function using contrast sweep visual evoked responses

AIM/BACKGROUND

The contrast sensitivity function (CSF) measurement provides information that is not accessible by standard visual acuity determinations. The contrast sweep pattern reversal visual evoked responses (CSVER) technique was used to objectively measure the CSF in clinical practice.

METHODS

The contrast thresholds were measured at five spatial frequencies in 10 normal subjects. The CSVER were recorded with sinusoidally modulated vertical gratings at 10 contrast levels (96, 64, 48, 32, 16, 8, 4, 2, 1, and 0.5%) presented in five spatial frequencies (0.5, 1.0, 2.0, 4.0, and 8.0 cycles per degree). Each of 10 contrast levels was displayed for 2 seconds at the desired spatial frequency. The CSVER amplitudes at the second harmonic were calculated by discrete Fourier transform. The results were compared with those obtained using a psychophysical method.

RESULTS

An inverted U-shaped CSF which peaked at 2.0 cycles per degree with a contrast sensitivity of 34.5 (contrast, 2.9%) was observed. The CSF assessed electrophysiologically was 0.62 to 0.79 log units lower than the sensitivity measured using the psychophysical method. However, the overall shapes were highly correlated.

CONCLUSION

One can objectively measure CSF with CSVER and this may be useful in patients in whom the psychophysical method is limited.

Comparison of preferential looking acuity and pattern reversal visual evoked response acuity in pediatric patients

BACKGROUND

We compared the visual acuities obtained with preferential looking (PL), the most widely used method of pediatric vision assessment, with those obtained with the spatial frequency sweep pattern-reversal visual evoked response (SPVER).

METHODS

Eighty patients (ages 1.5 months to 12 years) with various ocular pathologies participated in this study. The PL acuity was determined using the up-and-down staircase procedure. The PVER was recorded with the spatial frequency sweep method using 10 spatial frequencies; the acuity was determined by placing the best-fit regression line on the descending slope of the PVER amplitude-spatial frequency function toward the higher spatial frequency to the baseline.

RESULTS

The PL acuities ranged from 20/25 to < 20/1600 (mean 20/155). The correlation between the two methods was good (r = 0.847). Fifty-six patients (70%) had an acuity agreement within 1.0 octave. When the PL acuity was > 20/128, it was on average better than the PVER acuity. When the PL acuity was lower, the PVER acuity was usually better. This tendency was marked when the visual acuities were very poor (y = 0.552x + 0.362).

CONCLUSION

The methods correlate well, although there is a dissociation of acuities in the presence of very low vision. PVER may be a useful addition to PL in assessment of vision in infants and young children.

Comparison of Snellen acuity and objective assessment using the spatial frequency sweep PVER

BACKGROUND

We compared the vision objectively assessed by spatial frequency sweep pattern-reversal visual-evoked response (SPVER) with the Snellen acuity in patients.

METHODS

SPVER acuity and Snellen acuity were measured in 100 patients with various ocular pathologies, including macular diseases, diffuse retinal degeneration, optic nerve diseases, glaucoma, and high myopia. For SPVER, 10 sinusoidally modulated vertical gratings were presented as stimuli. The responses were averaged and displayed through the discrete Fourier transform on the monitor display. The PVER acuity was determined by extrapolating the SPVER amplitude-spatial frequency function to baseline.

RESULTS

Vision ranged from 20/15 to 20/400 with Snellen acuity, and from 20/25 to 20/190 with SPVER. The overall correlation between the two acuities was r = 0.666. The correlation varied from r = 0.895 in eyes with glaucoma to r = 0.436 in eyes with optic nerve disease. Seventy-seven eyes (77%) had a visual acuity agreement of within 1.0 octave between the two measurements.

CONCLUSION

The SPVER acuity and the Snellen acuity correlated to a certain degree. Discrepancies were found in certain diseases, with the highest disparity in patients with optic nerve disease. We conclude that the SPVER is effective in estimating vision objectively, particularly in patients in whom the standard Snellen test is impossible to perform or yields unreliable results.

Five years' experience with the Grating disc. A simplified method of evaluating vision in young children

The Grating Disc (GD) is a simplified visual test designed for children 18 months to 4 approximately 5 years. Two hundred pediatric patients (103 males, 97 females; aged 5 months to > 6 years) participated in this study to determined how the GD visual acuity (VA) correlates with the Preferential Looking (PL) VA. Forty-six percent of the patients had varying degrees of retinopathy of prematurity. The PL acuity was determined using the up-and-down staircase procedure. To measure GD acuity, six GDs with vertical gratings equivalent to acuities of 20/1920 to 20/60 were used. The examiner presented one GD simultaneously with the homogeneous disc from 57 cm. The VA was determined by the finest GD that the child could differentiate from the homogeneous disc. The overall correlation between the PL and the GD acuities was very high (R2 = 0.861). One hundred twenty-eight patients (64.0%) had an acuity agreement within 0.5 octave and 178 (89.0%) patients were within 1.0 octave. When the PL acuity was > or = 20/100, the GD and PL acuities showed good agreement. When the PL acuity was poorer, the GD acuity was poorer than the PL acuity. Although the GD acuity tended to be lower than the PL acuity in severely visually impaired patients, the GD acuity agreed with the PL in most visual assessments of young children. GD testing could be a useful alternative when sophisticated assessment systems such as the PL are unavailable.

Spatial tuning loss of pattern reversal visual evoked response in optic nerve disease

We compared the pattern reversal visual evoked response (PVER) amplitude-check size functions from 25 eyes (25 normal subjects; visual acuities > or = 20/20) with those from 32 eyes (22 patients; visual acuities 20/15 to 20/50; mean, 20/25.5) with mild optic nerve disease to determine if spatial tuning loss of the PVER occurs in the presence of optic nerve dysfunction. The steady-state PVER was recorded with five check sizes (range, 160 to 10 minutes of arc). To analyze the PVER amplitude-check size function, we calculated the difference between the maximum and minimum PVER amplitudes and then calculated the area of spatial tuning (the area under the function). Values were significantly smaller in patients than in normal subjects (1.81 +/- 1.27 microV versus 5.73 +/- 3.27 microV; F = 41.24, p = 0.0001; 3.87 +/- 2.70 area units versus 12.57 +/- 7.60 area units; F = 38.62, p = 0.0001). There was no shift in the distribution of peak check sizes. Results suggest that a spatial tuning loss occurs in optic nerve disease. The shape of the function, including the area of spatial tuning, appears to be a sensitive indicator of early or mild optic nerve dysfunction.

Spatial frequency sweep pattern reversal VER acuity vs Snellen visual acuity: effect of optical defocus

The effect of artificially induced image defocusing on visual acuities (VAs) measured by spatial frequency sweep pattern reversal visual evoked response (SPVER) and Snellen measurement was studied in six normal subjects. The steady-state SPVER was recorded using vertical gratings of 10 different spatial frequencies ranging from 0.52 to 30.36 c/deg. The SPVER acuity was compared with Snellen acuity (SA) measured under the same conditions of optical defocus. With moderate defocusing [< + 1.0 diopter (D), VA > 20/40], the SPVER acuities were equal to or poorer than the SAs. With more defocus (> + 1.5 D, VA < 20/70), the SPVER acuities became better than the SAs. The discrepancies between the SA and SPVER acuities may be the result of the influence of the parafoveal area on the SPVER at lower visual acuity levels.

Tonometry in pediatric patients: a comparative study among Tono-pen, Perkins, and Schiötz tonometers

Measuring the intraocular pressure (IOP) in children can be difficult. We compared the accuracy of IOP measurements in pediatric patients using three tonometers: Perkins, Schiötz, and Tono-pen. Seventy-seven children (132 eyes; average age, 1 year, 7 months; range, 1 month to 60 months), mainly afflicted with retinopathy of prematurity (107 eyes), were evaluated. A good correlation (r = 0.867) was found between the Tono-pen and the Perkins tonometers. No statistical difference was found between the mean difference of IOP values obtained with the Tono-pen and the Perkins (P > .05). The Schiötz measurements were significantly higher than those obtained with the Perkins and the Tono-pen tonometers (P < .05). We concluded that the Tono-pen tonometer has a higher correlation coefficient, comparable to the Perkins tonometer, and can be used reliably to assess IOP in pediatric patients.

Correlating preferential looking visual acuity and visual behavior in severely visually handicapped children

We developed a series of questions that reflects the functional abilities of severely visually handicapped children. The study population comprised 100 patients aged 30 to 60 months (mean 43.23), mostly afflicted with retinopathy of prematurity. Visual acuity was measured by preferential looking. Preferential looking acuities of the patients ranged from 20/25 (0.8) to 20/6400 (0.003) (mean 20/470 (0.04)). Ten activities were analyzed and correlated with preferential looking acuity. Among the selected visual activities, when children are not interested in television (p = 0.0001), toys (other than those that make sounds (p = 0.0001), and people (p = 0.001)), their preferential looking acuities were very low. For example, 73 out of 100 patients who were visually interested in television had preferential looking acuities (mean 20/245 (0.082)) that were significantly higher (p = 0.001) than 21 patients not interested in television (mean 20/2806 (0.007)). Patients with nystagmus (n = 79) had significantly lower preferential looking acuities (p = 0.0001) (mean 20/1114 (0.018)) than patients with no nystagmus (mean 20/57 (0.35)). When evaluating visual function in young, severely visually impaired patients, in addition to preferential looking testing, analyzing visual behavior within the environment is important to accurately evaluate their remaining visual abilities.

Contrast visual acuities in cataract patients. III. Changes of contrast acuity profiles in normal and pathological eyes

We compared pre- and postoperative visual acuities in 45 cataract patients without ocular pathology except lens opacity (group 1) and 20 patients with ocular pathologies and lens opacity (group 2) using Variable Contrast Visual Acuity Charts. Charts 1 and 4 have 90% contrast; chart 4 has white optotypes on a black background (reverse polarity), charts 2 and 3 have 15% and 2.5% contrast, respectively. The mean preoperative visual acuities of groups 1 and 2 measured with the high-contrast Landolt optotypes ranged from 0.02-0.80 and 0.22-0.40, respectively. Visual acuity improvements between the pre- and postoperative periods ranged from 1.37-1.61 and 0.52-1.24 octaves in groups 1 and 2, respectively, with the different charts. Visual acuity improvement was poorest with chart 3. The group 1 mean preoperative visual acuity measured with chart 2 was 1.11 octaves lower than with chart 1. In group 2, the visual acuity reduction was 1.81 octaves. The relation between the visual acuities measured with the high-contrast intermediate-contrast optotypes are important for predicting postoperative visual acuity improvement. An abnormal contrast acuity profile may indicate the presence of additional ocular pathologies.

Pattern-reversal visual-evoked response in bull's eye maculopathy associated with Stargardt's disease

Using steady-state pattern-reversal visual-evoked response (PVER), we studied the macular function in patients with bull's eye maculopathy. The results were correlated with fluorescein angiography. Study patients with an established (25 eyes of 14 patients) and a suspected (8 eyes of 4 patients) diagnosis of Stargardt's disease with bull's eye maculopathy were divided into group G (good vision group: 15 eyes with visual acuity of 20/40 or better) and group P (poor vision group: 18 eyes with visual acuity of 20/50 or worse). The diameters of the atrophic area and the normal or less affected central area of the bull's eye were measured form the fluorescein angiograms. The mean diameter of the central area in group G (2.0 degrees) was significantly larger than that in group P (0.6 degrees; d.f. = 17, p = 0.0227). The PVER amplitudes were reduced in the patient groups with all check sizes and the amplitude-check size functions were flat. Amplitude differences were observed between the patient groups with the 20' checks (d.f. = 17, p = 0.0638), probably due to the difference in the mean central diameters (2.0 degrees vs. 0.6 degrees). Patients with a perifoveal abnormality can have an abnormal PVER despite relatively good visual acuity. We also recorded the PVER in 7 normal controls tested with simulated ring-shaped scotomas, the sizes of which matched the mean diameters of the scotomas in the patient groups (7.0 degrees x 0.6 degrees and 7.0 degrees x 2.0 degrees). The controls also showed markedly reduced responses with all check sizes.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of electroretinographic and fluorescein angiographic findings in unilateral central retinal vein obstruction

BACKGROUND

In central retinal vein obstruction (CRVO), electroretinogram (ERG) abnormalities and extensive retinal capillary dropout (CD) in the fluorescein angiogram (FA) are good indicators of retinal ischemia. We retrospectively studied patients with unilateral CRVO and compared the ERG and FA results.

METHODS

Single white flash ERG, photopic ERG, scotopic ERG and flicker ERG were recorded in 30 cases of unilateral CRVO. We analyzed the correlation between the ERG results and the presence/absence of extensive CD.

RESULTS

The ERG b/a-wave amplitude ratios, photopic and scotopic b-wave amplitudes, and flicker amplitudes were significantly smaller (P < 0.05) in eyes with extensive CD (n = 12, 40%), than in eyes without (n = 18, 60%). When the photopic or scotopic b-wave amplitudes were normal or supernormal, extensive CD on FA was absent in all eyes. When the b/a-wave ratios were > or = 1.0 or when the b-wave amplitudes with white flash or flicker amplitudes were normal or supernormal, extensive CD was present in less than 32% of eyes.

CONCLUSION

These results suggest that the ERG results, especially the b/a-wave amplitude ratio, are significantly correlated with the presence/absence of CD on FA in CRVO.

Pattern reversal visual evoked response and Snellen visual acuity

Because the pattern-reversal visual evoked response (PVER) reflects the central retinal function, PVER results generally agree with those of psychophysical tests. The visual acuities (VAs) calculated from PVER recordings and Snellen acuity (SA) measurements were compared in 500 eyes (261 patients; ages 8 to 88 years; mean, 44.5 years). The best-corrected VA was measured using the ETDRS chart, and the PVER acuity was determined by the smallest check size that produced a definite PVER (critical check size). In 288 eyes with a critical check size of 10 min of arc, the SAs ranged from 20/15 to 20/800 (mean 20/38). In 68 eyes with a critical check size of 20 min, the SAs ranged from 20/15 to 20/800 (mean 20/97). In 70 eyes with a critical check size of 40 min, the SAs ranged from 20/20 to 20/1600 (mean 20/156). In 29 eyes with a critical check size of 80 min and 14 eyes with a critical check size of 160 min, the SAs ranged from 20/50 to 20/1600 (mean 20/312 and 20/398, respectively). In 31 eyes in which the PVER was non-recordable, the SAs ranged from 20/70 to 20/3200 (mean 20/1177). The PVER acuity using the smallest check size seemed to agree with the SA, but large deviations were observed in certain subjects.

Electroretinogram b/a wave ratio improvement in central retinal vein obstruction

The electroretinogram (ERG), especially the b/a wave ratio, is considered a good indicator of retinal ischaemia in central retinal vein obstruction (CRVO). Seven CRVO patients who showed b/a wave ratio improvement from < 1.0 [negative type (-) ERG] to > or = 1.0 and one from 1.07 to 1.53 were studied. Three mechanisms of change were observed: firstly, the b-wave amplitude increased without an a-wave amplitude decrease (group A, n = 2); secondly, the b-wave amplitude increased with an a-wave amplitude decrease (group B, n = 4); and, thirdly, both decreased, but the a-wave amplitude decreased more markedly (group C, n = 2). In group A, the visual acuities improved markedly. In group B, the visual acuities improved in two cases in which the b-wave amplitude reached the normal range; the visual acuities did not improve in two cases in which the b-wave amplitude did not reach the normal range. In group C, the visual acuities remained poor. The negative (-) ERG or significantly reduced b/a wave ratio is associated with ischaemic CRVO and did not occur because of the filtering effect of the haemorrhage, which may reduce the stimulus light for the ERG. Improvement of the reduced b/a wave ratio with an increased b-wave amplitude was accompanied by improvements in fundus appearance and visual acuity in CRVO. The results suggest that the retinal ischaemia in CRVO, as revealed by the ERG and fluorescein angiogram, may be reversible in some cases.

Prognostic value of initial electroretinogram in central retinal vein obstruction

We retrospectively studied the correlation between the initial electroretinogram (ERG) recordings and the final visual acuities (VA) of 47 patients with central retinal vein obstruction (CRVO) after follow-up of more than 1 year. The a- and b-wave amplitudes and the b/a ratio with white flash were significantly larger in patients with good vision (VA > 20/200) than in those with poor vision (VA < or = 20/200). The b/a ratio and b-wave amplitude with white flash showed sensitivity and specificity of more than 78% for visual prognosis. The latest VA was < or = 20/200 in all 20 patients with a subnormal b-wave amplitude and in all 15 with b/a ratio < 1.05. These results suggest that the ERG recorded soon after (CRVO) onset correlates strongly with visual prognosis.

Snellen visual acuity versus pattern reversal visual-evoked response acuity in clinical applications

We compared the best-corrected Snellen acuity (SA) and the pattern reversal visual-evoked response (PVER) acuity in normal subjects and patients. Forty-two eyes of 42 normal subjects were controls; 457 eyes of 329 patients comprised the patient group. A steady-state stimulus with five check sizes ranging from 160 to 10 min in 1.0-octave steps was used. The PVER acuity was derived from the best-fit linear function relating the amplitude to the log-adjusted check size. Three intercepts of 0, 1 and 2 microV were used in both groups, and the PVER acuities were called P0, P1 and P2. The SAs in normal subjects ranged from 20/15 to 20/20 (mean, 20/18.3) and in patients from 20/15 to 20/1,600 (mean, 20/56.9). In normals, the P0 showed the best agreement with the SA (mean acuity difference, +0.34 octave). The SA and P0 agreed within +/- 2.0 octaves in 33/42 (78.6%) eyes. In patients, the P0 also showed the best agreement with the SA; 306/457 (67.0%) eyes showed an acuity difference within +/- 2.0 octaves. Unlike normals, 83/457 (18.2%) eyes showed an acuity difference > -3.0 octaves. These eyes mostly had optic nerve disease with a flattened PVER amplitude-check size function curve. The P0 seems to correlate better with SA than P1 and P2, but this analytical method may be less effective in the presence of certain pathologic conditions.

Effects of light scatter, defocusing, mean luminosity, contrast, and central scotoma on the PVER amplitude-check size function curve

We analyzed the effects of various stimulus parameters, ie, light scatter, defocusing, mean luminosity, contrast, and central scotoma, on the normal pattern reversal visual evoked response (PVER), amplitude-check size function curve in six normal subjects. The steady-state PVER was recorded with five check sizes ranging from 160 to 10 min in 1-octave increments. The PVER amplitude, especially with the smaller check sizes, was markedly decreased by light scatter induced by acrylic sheets. The function curve quickly changed to a low pass filter shape when +2.0 diopters of defocus were added, with the decrease most marked in the small check sizes. When the mean luminosity was decreased, the function curve maintained its normal inverted-U shape up to 5 cd/m2, but the shape flattened with lower luminosity. Amplitude decreases were seen with all check sizes in low luminosity. With contrast changes from 95 to 24%, the function curve maintained its normal shape, but with slightly reduced amplitudes. The amplitude decrease was moderate even with the lowest contrast. With a two-degree central scotoma, the PVER amplitude was reduced more with the smaller than the larger check sizes. The function curve became somewhat flatter, with its peak shifting to the larger check sizes. Results indicated that the shape of the PVER amplitude-check size function curve changes in response to different modes of stimulation.

Stargardt's disease/fundus flavimaculatus: psychophysical and electrophysiologic results

Retinal functions were analyzed psychophysically and electrophysiologically in 73 patients (146 eyes) with Stargardt's disease/fundus flavimaculatus. Patients were classified into types 1, 2, 3, and 4; patients with type 3 were subdivided into 3E and 3L (early and late onset of initial symptoms). Most had visual acuity (VA) of 20/200 or greater at initial testing. VA declined 0.25 octave/year during follow-up (mean, 6.1 years). Four of 16 patients (25%) older than 40 years had VA of 20/200 or less in the stronger eye. Psychophysical tests (flicker profile, central scotoma, dark adaptation) showed variable degrees of abnormalities. Electrophysiological tests showed significant photopic b-wave amplitude decreases, particularly in type 3E (42.2% of normal). The electro-oculogram light peak/dark trough ratio was abnormal in 60 of 132 eyes (45.5%), especially in type 3E (25 of 34 eyes, 73.5%). Visual prognosis and overall visual function varied depending upon disease type, location of retinal lesions, and age of onset. In Type 3E, overall retinal function was poorest and accompanied by the most severe decline of central vision and function in the surrounding macula.

Glaucoma as a cause of poor vision in severe retinopathy of prematurity

Despite surgical reattachment of the retina in infants with severe retinopathy of prematurity (ROP), visual acuity may decline. We performed gonioscopy and applanation tonometry on 26 eyes of 17 infants with severe ROP who were randomly selected and followed prospectively for 2 years. Of these 26 eyes, one eye of one patient had only peripheral retinocryopexy for threshold stage III disease and had an attached retina before enrollment into the study. Sixteen infants subsequently underwent vitrectomy, scleral buckle, or both. Retinal reattachment of the posterior pole was present in at least one eye each of 10 of the 17 infants. Glaucoma was diagnosed in 5 of the 10 patients; all 5 showed a decrease in visual acuity of greater than 1 octave. Of the 5 infants without glaucoma, 3 showed visual improvement, and 2 remained the same. Although we studied a small number of cases, our results suggest that glaucoma may be a cause of visual decline in infants with severe ROP. A decline in visual acuity in infants with severe ROP and surgical retinal reattachment may warn us of glaucoma, as this diagnosis is difficult to make in these small infants.

Retinal detachments in incontinentia pigmenti

We report on retinal detachments in six eyes of four patients with incontinentia pigmenti. These nonrhegmatogenous traction retinal detachments are characterized by extensive preretinal and vitreous fibrous organization that pull the retina anteriorly behind the lens. The clinical course and fundus appearance of the retinal detachments, beginning with the avascular peripheral retina and leading to traction retinal detachment, are similar to those of cicatricial retinopathy of prematurity. Vitreous surgery was performed on three eyes (two patients), with partial reattachment of a total retinal detachment in one eye and complete reattachment of a partial retinal detachment in a second eye. These cases represent the first successful surgical interventions reported for retinal detachment in incontinentia pigmenti.

Vision in stage 5 retinopathy of prematurity after retinal reattachment by open-sky vitrectomy

Performing vitrectomy in stage 5 retinopathy of prematurity is controversial, partially due to limited anatomical and poor reported visual results. Fifty-five eyes of 50 patients whose retinas were reattached by open-sky vitrectomy in stage 5 retinopathy of prematurity and who were followed up for more than 12 months were analyzed retrospectively to ascertain clinical factors that may influence visual outcome. Vision was evaluated by preferential looking. Visual ability to discriminate stationary objects was obtained in 32 (58.2%) eyes, 18 (32.7%) had motion perception, and five (9.1%) had light stimulus perception. Although visual acuities were relatively low, they were useful to these patients. Age at the time of vitrectomy and the shape of the retinal detachment were found to be important factors in predicting visual prognosis.

Measuring vision with temporally modulated stripes in infants and children with ROP

PURPOSE

To determine differences in preferential looking (PL) acuities using stationary and temporally modulated stripe patterns in patients with various stages of retinopathy of prematurity (ROP).

METHODS

We measured the PL acuities of 134 patients (ages 4 mo to 13 yr) with various stages of ROP. Patients were divided into six subgroups according to PL vision measured with stationary stripes: (1) equal to or better than 20/200 (n = 24); (2) worse than 20/200 to 20/400 (n = 10); (3) worse than 20/400 to 20/800 (n = 15); (4) worse than 20/800 to 20/1600 (n = 13); (5) worse than 20/1600 to 20/6400 (n = 26); and (6) worse than 20/6400 (n = 46; no stationary vision).

RESULTS

In the group with PL acuity equal to or better than 20/200, no difference in vision was apparent between the two methods. In patients with acuities worse than 20/200 to 20/400, the temporally modulated PL acuities were 0.23 octave better than the PL acuities measured with the stationary stripes. The difference increased to 0.86 and 1.12 octaves in the groups with visual acuities worse than 20/400 to 20/800 and worse than 20/800 to 20/1600, respectively. The difference in the group with PL acuities worse than 20/1600 to 20/6400 was 1.69 octaves. The 46 patients with no stationary vision detected only the temporally modulated stripes.

CONCLUSIONS

The results suggest that the PL acuity difference between the temporally modulated and stationary stripes increases with visual impairment. Measuring PL acuity with temporally modulated stripes is an important addition to the evaluation of severely visually impaired subjects.

Effect of hemifield stimulation on simultaneous steady-state pattern reversal electroretinogram and visual evoked response

Steady-state pattern reversal electroretinograms (PERG) and pattern reversal visual evoked responses (PVER) were recorded simultaneously in 4 normal subjects using hemifield stimulation of the upper/lower and nasal/temporal conditions with 95 and 60% stimulus contrasts. A square-wave checker-board pattern (check size 40 min of arc) was used. The temporal frequency (reversal rate) was 6 Hz (12 reversals/s). With nasal/temporal hemifield stimulation, neither the PERG nor the PVER amplitudes differed significantly with either stimulus contrast. With the upper/lower hemifield stimulation, PERG amplitudes were not significantly different; PVER showed a significantly larger amplitude for lower than for upper hemifield stimulation with both contrasts (ANOVA test: p = 0.0064, 95% contrast; p = 0.0018, 60% contrast). PVER amplitudes recorded with lower hemifield stimulation were 2.05 and 2.63 times larger than those elicited with upper hemifield stimulation, for the 95 and 60% contrasts, respectively. The difference in response to the upper/lower hemifield stimulation, observed only in PVER, suggests that the lower stimulus field dominancy may be processed in a visual pathway proximal to the retinal level.

Correlating visual acuity and electrooculogram recordings in Best's disease

The visual function in 54 eyes of 27 patients with Best's disease was analyzed by retrospectively examining the Snellen visual acuities and the electrooculogram (EOG). Visual acuities, generally well maintained in most patients, were 20/40 (0.5) or better in 41 of 54 (75.9%) eyes, and showed no correlation with age. Those in the cicatricial stage had worse visual acuities than those in the previtelliform stage. The EOG was abnormal in 47 eyes (87.0%) with a subnormal light peak/dark trough (Lp/Dt) ratio less than 1.85. Seven eyes (13.0%) with an Lp/Dt ratio 1.85 or higher had significantly smaller Dt values compared with those with a low Lp/Dt ratio. The Lp/Dt ratio did not correlate with patient age or disease stage. No correlation existed between visual acuities and Lp/Dt ratios. The Lp/Dt ratio did not reflect the severity of the macular lesions. The results indicate that not only a low Lp/Dt ratio but also a low dark trough value in cases with a normal Lp/Dt ratio are helpful in diagnosing Best's disease.

Visual hand display (VHD) as an introductory procedure for measuring vision in infants and young children with visual impairment

We developed the Visual Hand Display (VHD) to measure vision in visually impaired infants and young children. The VHD is a circular fabric mitten, which is held easily by inserting the hand between the two surfaces. Black-and-white stripes are attached to one surface, 25, 15, 10, 4, and 2 mm per stripe. The VHD acuity is determined by the shortest test distance and the smallest stripes that the patient can detect. The VHD acuities were compared with preferential looking (PL) staircase acuities in 130 patients (53 males, 77 females; age range, 2 to 13 years; median, 21.0 months). Of these, 107 (82.3%) had various degrees of retinopathy of prematurity. The correlation between the VHD and the PL acuities was high (R2 = 0.849). PL acuities were better than the VHD acuities in 98/130 patients (75.4%), with an average difference of 0.51 (SD = 0.70) octave. The visual acuity differences were more pronounced in subjects with slight visual impairment and much less in subjects with severe visual impairment. The VHD seems to be an effective introductory method to evaluate visual acuity in severely visually impaired infants and young children. This method also would be effective with severely mentally and physically disabled patients who cannot undergo PL testing.

Aniseikonia and stereoacuity in pseudophakic patients. Unilateral and bilateral cases

PURPOSE

To evaluate the efficacy of intraocular lens (IOL) implant procedures, analyzing visual function of the operated eyes and the resulting binocular vision.

METHOD

The authors measured aniseikonia and stereoacuity in patients with both bilateral and unilateral posterior chamber intraocular lenses (PC IOLs). The aniseikonia was measured with the New Aniseikonia Test; the stereoacuity was evaluated with the Titmus Stereotest.

RESULTS

In 41 patients with bilateral PC IOLs, aniseikonia measured with the New Aniseikonia Test ranged from 0% to 4% (mean, 0.76%; standard deviation = 1.04%). The average stereoacuity evaluated with the Titmus test was 7.68 circles (less than 60 seconds; range, greater than 800 to 40 seconds of arc), with 36 of 41 patients (87.8%) showing a stereoacuity less than or equal to 100 seconds of arc. In 37 patients with unilateral PC IOLs, the aniseikonia ranged from 0% to 6% (mean, 0.97%; standard deviation = 1.13%). Their stereoacuity also ranged from greater than 800 to 40 seconds (mean, 7.67 circles) (less than 60 seconds). In this group, 34 of 37 (91.8%) patients showed a stereoacuity less than or equal to 100 seconds of arc.

CONCLUSION

Although the problem of aniseikonia still remains, a significant number of patients attain good binocular function after unilateral and bilateral PC IOL implantation.

Contrast visual acuities in cataract patients. II. After IOL implantation

Contrast visual acuities were measured in 100 eyes of 75 patients who attained a best-corrected visual acuity of greater than or equal to 0.8 (20/25) after intraocular lens (IOL) implantation. The variable contrast visual acuity chart (VCVAC), with three contrast levels of 90, 15, and 2.5% and reverse polarity of 90% contrast, was used to measure contrast visual acuities. The follow-up period ranged from 3 to 35 months (mean 7.41). The mean visual acuities measured with the 90, 15, and 2.5% charts were 0.92 (SD = 0.11), 0.59 (SD = 0.13), and 0.33 (SD = 0.14), respectively. The mean visual acuity measured with the 90% reverse polarity chart was 0.97 (SD = 0.11). The decreases in visual acuities compared with the 90% contrast were 0.64 and 1.48 octaves in the 15% and the 2.5% contrast charts, respectively. The pattern of the contrast acuity profile was comparable to normal subjects, but in 28 of 100 (28%) eyes, the visual acuities measured with the reverse polarity chart were slightly better than those measured with the standard 90% contrast chart, suggesting that the glare effect still exists after IOL implantation, though to a lesser degree than in cataractous eyes.

Effect of light scatter on the pattern reversal visual evoked response: comparison with psychophysical results

The effect of light scatter on the pattern reversal visual evoked response (PVER) was studied in 6 normal subjects. The results were compared with contrast visual acuity, contrast sensitivity function, and glare disability. Light scatter was induced by translucent acrylic sheets. Visual acuity measured with the low-contrast charts decreased significantly (P < 0.0001) even with a small degree of light scatter. Contrast sensitivity decreased with a small degree of light scatter especially for high spatial frequencies. PVER amplitudes decreased especially at the smaller checks with its peak shifted to larger checks. PVER was equally sensitive to light scatter compared to psychophysical tests.

Contrast visual acuities in cataract patients. I. Comparison with normal subjects

Contrast sensitivity and glare sensitivity are often abnormal in cataract patients. However, despite significant subjective complaints, relatively good visual acuities often are obtained with high-contrast optotypes. Using Variable-Contrast Visual Acuity Charts (VCVAC), we measured visual acuities of 40 eyes of 24 normal subjects (visual acuity greater than or equal to 1.0) aged 41 to 72 years, and 40 eyes of 28 cataract patients (visual acuity greater than or equal to 0.6) aged 44 to 81 years. The VCVAC consists of 4 different charts (1-4). The contrast is 90% in charts 1 and 4, 15% in chart 2 and 2.5% in chart 3. Chart 4 is the reverse polarity of chart 1. The decrease of visual acuity compared with the high-contrast chart (chart 1) was larger in the cataract group with both in the 15% contrast (0.52 vs. 0.71 octave) and the 2.5% contrast (1.21 vs. 1.75 octaves). In cataract group, 23/40 eyes (57.5%) showed better visual acuity with chart 4 than that of chart 1. In addition to high-contrast optotypes, acuity measurements using intermediate- to low-contrast optotypes, combined with the reverse polarity chart, seem effective in analyzing the visual disabilities caused by early cataract.

Pattern reversal visual-evoked response as a prognostic indicator in macular gliosis

We recorded the preoperative pattern reversal visual-evoked responses in 16 subjects (16 eyes) with macular gliosis who underwent membrane-peeling operations. A postoperative visual improvement of one octave or more was observed in 11 of 16 eyes (68.8%). Preoperatively, ten eyes had peak amplitudes greater than or equal to 2 microV, all 11 eyes had either lowpass or bandpass curve shapes, and ten eyes had recordable responses to 20- or 10-minutes of an arc check sizes. Each of the three preoperative criteria was significantly associated with a postoperative visual improvement of one octave or more (P = .01, .02, and .02, respectively). These results demonstrate that the preoperative pattern reversal visual-evoked response can objectively assess the function of the underlying macula in patients with macular gliosis and, consequently, is helpful in determining which patient would most likely benefit from a membrane-peeling operation.

Effect of stimulus contrast on simultaneous steady-state pattern reversal electroretinogram and visual evoked response

We studied the effect of stimulus pattern contrast on the simultaneously recorded pattern reversal electroretinogram (PERG) and pattern reversal visual evoked response (PVER) at 5 check sizes. The stimulus contrast ranged from 24 to 95% in 6 steps of 0.1- or 0.15-log unit increments. PERG amplitude showed a linear increase with an increase in pattern contrast at all check sizes. PVER amplitude showed an increase up to a certain pattern contrast, but was saturated upon further increase in stimulus contrast at all check sizes. The PERG amplitude-check size function curve showed a flattened, inverted-U shape only with the highest contrast and low-pass filter shape or flat shape with lower contrasts. The PVER amplitude-check size function curve showed an inverted-U shape (bandpass filter shape) at all contrasts. These characteristics to the changes in contrast and the spatial frequency tuning suggest that PVER is processed in a different location of visual pathway than PERG.

Electrophysiological findings in paraneoplastic retinopathy

Paraneoplastic retinopathy is a cancer-related non-metastatic retinopathy mainly associated with lung cancer. We examined two patients with presumed paraneoplastic retinopathy, both ophthalmologically and electrophysiologically. Both patients presented with initial visual complaints of moderate reduction of visual acuity. No specific fundus anomaly was found in the fundus except for a mild attenuation of the retinal arteries. The electroretinogram and pattern reversal visual evoked responses were either markedly reduced in amplitude or non-recordable. The electrooculogram recorded in one patient demonstrated a markedly reduced light peak/dark trough ratio. These results indicate the presence of a severe and diffuse bilateral retinal dysfunction, despite the relatively good visual acuities and mild fundus changes. Electrophysiological evaluations play an important role in the diagnosis of paraneoplastic retinopathy.

Gyrate atrophy of the choroid and retina in a 5-year-old girl

A 5-year-old Asian-Indian female presented with bilateral cobblestone-like peripheral lesions, a single area of chorioretinal atrophy, infero-nasal to the disc, in her right eye and a non-recordable single flash ERG. Serum ornithine level was assayed at 841 mumol/l, ten times normal levels, and a diagnosis of gyrate atrophy, due to ornithine aminotransferase deficiency was made. The patient was refractory to any form of therapy and her clinical lesions spread rapidly in both eyes, showing both centrifugal and centripetal spread in her right eye. A rapid deterioration in her psychophysical tests was also seen over the 28 months follow-up. The presence of cobblestone-like peripheral lesions in a child should alert the clinician to the possibility of gyrate atrophy, and the rapid spread of the chorioretinal lesions coupled with non-recordable single flash ERGs, in a young patient may suggest a much poorer prognosis.

Development of vision in retinopathy of prematurity

Serial measures (range, two to eight) of preferential-looking grating acuities of 52 infants with retinopathy of prematurity were made. Group 1 patients (n = 11), who had little or no macular displacement, had normal preferential-looking acuity except for two who had mild acuity deficits. None of the group 2 patients (n = 12), who had dragged maculas, ever had normal acuity. On the average, their acuities, which ranged from 1 to 6 octaves less than normal, gradually increased at a rate not significantly different from normal. Group 3 patients (n = 29), who had undergone open-sky vitrectomy, had significantly lower acuity despite reattachment of the retina.

Topographical analysis of peripheral vs central retina with pattern reversal visual evoked response and the scanning laser ophthalmoscope

The contribution of the central and the surrounding peripheral retina to the pattern reversal visual evoked response (PVER) was analyzed simultaneously using double frequency stimulation and the Fast Fourier transform (FFT) method. The Scanning Laser Ophthalmoscope (SLO) was used to project the pattern stimulus, a square subtending 10 degrees on a side, on a specific location in the fundus and to monitor accurately the stimulus' position during PVER testing. When the stimulus area on the central retina was less than or equal to 50 min of arc on a side, or 0.69% of the total area was stimulated (a square of 10 degrees on a side), the contribution from the central retina was negligible, and the PVER was dominated by surrounding peripheral retinal activity. When the stimulus area of the central retina was greater than or equal to 100 min of arc on a side, or 2.78% of the whole area was stimulated, activity from the central retina became more evident. When the stimulus area projected on the central retina became 150 min on a side (6.25% of the area or greater), activity from the central retina showed an increase and exceeded that of the peripheral retina. When the central area became larger, its activity dominated the PVER, and the contribution from the peripheral retina became negligible at this stage. The PVER was highly dependent upon the activity of the central retina, and activity levels from the central and surrounding peripheral retina were correlated.

Retinal function in birdshot retinochoroidopathy

The electroretinograms (ERGs) of 15 patients with birdshot retinochoroidopathy varied from super-normal to non-recordable, depending upon the severity and the stage of the disease. The abnormal ERGs were characterized by a disproportionate decrease of the b-wave amplitude compared with the a-wave amplitude, demonstrating the negative (-) type response. This distinct ERG pattern has not been observed in any other type of uveitis or chorioretinitis, and appears specific to birdshot retinochoroidopathy. ERG findings indicate that in birdshot retinochoroidopathy the neural layers of the retina are more diffusely and severely involved than the receptor-retinal pigment epithelium-choroid complex. In the most advanced stage, the patients becomes night blind with a non-recordable ERG, a situation that is essentially the same as retinitis pigmentosa, except that pigmentation is conspicuously absent in the fundus.

Best's macular dystrophy with a macular hole

The occurrence of a macular hole with Best's dystrophy is an extremely rare finding with only one reported case in the literature. We wish to report two cases with typical Best's dystrophy in one eye and a macular hole in the contralateral eye. In one case the Pattern Reversal VER (PVER) was also recorded and graphed as an amplitude-check size function curve. The PVER changes in this case were grossly subnormal in both the eyes, suggesting a significant degree of bilateral macular impairment. This implies that a significant amount of functional impairment occurs at the vitelliform stage itself, though how this stage progresses to a macular hole is unclear.

Electrooculogram in central retinal vein obstruction

The electrooculograms (EOGs) of 24 patients with central retinal vein obstruction (CRVO) were correlated with fundus appearance and with the electroretinogram (ERG) b/a wave ratio. Of the 24, 17 (70.8%) showed abnormal EOGs [light peak versus dark trough ratio (Lp/Dt) of less than 1.85]. The EOG Lp/Dt ratio was abnormal in 64.7%, although the ERG b/a ratio was within normal limits. Though the exact mechanism is still not entirely clear, the EOG became abnormal in most patients with CRVO and correlated well with the severity of the disease.

Electrophysiological findings in peripheral uveitis

Nine patients with peripheral uveitis were studied clinically and electrophysiologically. Electroretinographic findings varied widely from supernormal to nonrecordable responses, depending on the disease duration and severity. These results suggest that the pathology in peripheral uveitis is not necessarily limited to the inferior pars plana but can be diffuse and widespread. In the final stage of the disease, the fundus showed extensive pigmentation and narrow retinal arteries associated with a nonrecordable electroretinogram, similar to retinitis pigmentosa. Burned-out peripheral uveitis should be considered in the differential diagnosis of secondary pigmentary degeneration.

Grating Discs: a simplified method of testing vision in infants and young children

We have developed a simple new method of evaluating visual function in young children about 15 to 36 months of age. Our Grating Discs system consists of six discs with a striped pattern and one homogeneous disc. One striped disc and the homogeneous disc are presented simultaneously, and the examiner observes whether the subject can discriminate between the two. The patterned discs have vertical stripes of different widths from 16 to 0.5 mm. At a testing distance of 57 cm, the visual resolution required for discriminating the grating ranges from 96 min of arc (0.01) to 3 min of arc (0.33) in one-octave steps; at a testing distance of 114 cm the required resolution ranges from 48 min (0.02) to 1.5 min (0.67). Using this system, we evaluated the visual acuity of normal infants and young children. Their ability to discriminate the finer gratings improved with increasing age, and more than 90% of the normal subjects in the 36-month group tested at 0.67. We also examined young children with known ocular pathologies and compared the results with acuity measurements obtained with the preferential looking test. The latter method gave acuities slightly better than those from the Grating Disc system, but the finding with the two techniques were generally in good agreement. Grating Discs are a simple, compact, effective tool for rapid assessment of visual function in young children.

Simultaneous pattern reversal ERG and VER recordings. Effect of stimulus field and central scotoma

The effects of the sizes of the stimulus field and of an artificially created central scotoma on simultaneously recorded pattern-reversal electroretinogram (P-ERG) and pattern-reversal visual-evoked response (P-VER) were investigated. With an increase in the stimulus field from 4 degrees X 4 degrees to 12 degrees X 12 degrees, the amplitude of the P-ERG increased steadily. The amplitude of the P-VER also showed an increase up to a stimulus field of 6 degrees X 6 degrees or 8 degrees X 8 degrees, but showed no increase with further expansion of the stimulus field. A central scotoma, created by placing a square of black paper at the center of the 12 degrees X 12 degrees stimulus field, was increased from 4 degrees X 4 degrees to 10 degrees X 10 degrees by 2-degree increments. Amplitudes of both the P-ERG and the P-VER decreased with increasing central scotoma size. The P-VER decreased significantly with a 4 degrees X 4 degrees central scotoma. Although both the P-ERG and the P-VER were influenced by the overall stimulus field and the central scotoma, there was a distinct difference in their behavior. The P-VER showed saturation above a certain stimulus field size and, with a central scotoma of 4 degrees X 4 degrees, much more reduction than the P-ERG, suggesting that the P-VER depends more on the macular area than does the P-ERG. The P-ERG also exhibited a substantial macular dependency, which, however, was not as great as that of the P-VER. The greater macular dependency of the P-VER compared to the P-ERG, as observed in our study, reflects the larger anatomic representation of the macula at the higher visual level.

Effect of optical defocus on the steady state pattern reversal visual-evoked response

The effects of optical defocusing with convex lenses on the amplitudes of pattern reversal visual-evoked response (PVER) were investigated. With the large check size and high-contrast pattern, PVER amplitudes showed a linear decrease in response to initial defocusing up to +5 to +6 dptr. As the degree of defocus increased, the PVER amplitude, though irregular, continued to show reliable, definite responses up to +25 dptr. With the intermediate check size and pattern contrast, PVER amplitudes displayed a linear decrease, but unlike the large-check/high-contrast condition, diminished to noise level after a defocus of greater than +4 to +5 dptr. From these results, we speculate that two phases in this function curve derive from the large-check/high-contrast condition: first, the contrast- or contour-dependent phase, and, second, the luminosity/movement-dependent phase.

[Fourier analysis of binocular VEP with stimulation of fusional areas]

Dioptic stimulation, by which each eye was stimulated by the same checkerboard pattern but at different pattern reversal rates, was performed and the visually evoked potentials (VEP) were analyzed with a Fourier processor. When both images from each eye were superimposed using fusional targets and prisms, the intermediate frequency component (IFC) was recognized besides two components corresponding to each stimulating frequency reversal rate. The relationship between IFC and the superimposed area (SA) was studied. IFC appeared clearly when the visual angle of SA was above 60 min. (18% of SA). The amplitude of IFC was saturated at a visual angle of 140 min. (53% of SA). Furthermore, when the SA was 200 min. of the visual angle (100% of SA), the IFC showed 0.6 times the activity of the monocular component. When dioptic stimulation was used, only one component corresponding to the stimulating pattern rates was observed and the amplitude became higher with increase of SA. The amplitude of the SA (areas of each eye were fully superimposed) was 1.4 times greater than that of 0% SA.

Electroretinographic findings in fellow eyes of patients with central retinal vein occlusion

In the study of 50 patients with unilateral central retinal vein occlusion, abnormal electroretinograms were observed in the fellow eyes of 18 patients (36%). The abnormal electroretinograms were supernormal in 15 patients (30%) and negative (+) in the fellow eyes of 3 patients (6%). The amplitudes of a and b waves were significantly greater in the fellow eye than those in normal controls. During a 1- to 9-year follow-up, central retinal vein occlusion developed in three fellow eyes (6%). The abnormal electroretinograms in the fellow eyes reflected such factors as circulatory disturbance of the retina that might have led to central retinal vein occlusion in the affected eye.

Recording pattern reversal visual evoked response with the scanning laser ophthalmoscope

We recorded visual evoked responses (VERs) to alternating, checkerboard pattern stimuli using the scanning laser ophthalmoscope (SLO). Retinal position and focus of checkerboard stimuli were monitored on the SLO video monitor throughout testing. Checkerboard size, check size, and retinal positions were varied. Consistent with other, well-established pattern reversal techniques, the SLO method produced: 1) reliable VERs with amplitudes of 2 to 10 microvolts, 2) maximum amplitudes at an intermediate check size for a fixed overall pattern size, and 3) variations in VER amplitude depending on stimulus retinal position relative to the fovea. Hence, the SLO-VER technique would be useful for clinical VER measurements when precise retinal stimulus position and focus are desired.