Diagnostic accuracy and variability of autorefraction by the Tracey Visual Function Analyzer and the Shin-Nippon NVision-K 5001 in relation to subjective refraction

Purpose:  To determine the accuracy of distance autorefractions obtained by two 'open field' devices, the Tracey Visual Function Analyzer and the Shin-Nippon NVision-K 5001, by comparison with subjective refraction.
Methods:  Both eyes of 50 healthy phakic participants underwent subjective refraction. Autorefractions were then performed on undilated pupils using the Tracey and a modified Shin-Nippon autorefractor and these were repeated within 50 days. Agreement with subjective refraction was calculated for sphere, mean spherical equivalent (MSE) and cylindrical vectors J ₀ and J ₄₅. Intratest and intertest variability were also evaluated.
Results:  The mean age of the participants was 37.4 years. Subjective refraction MSE ranged from −6.25 D to +3.62 D, mean −0.49 D ± 1.79 D. Bias between subjective refraction and Tracey was −0.001 D, +0.045 D, +0.017 D, and −0.015 D for sphere, MSE, J ₀ and J ₄₅ respectively; these were not significant. Bias between subjective refraction and Shin-Nippon was +0.004 D, +0.033 D, +0.106 D, and −0.021 D; only the J ₀ vector was significantly different ( p  < 0.0001) although this difference was small. Intratest variability for Tracey was low, measured at 0.189 D for sphere and 0.178 for MSE, and for the Shin-Nippon 0.099 D and 0.086 D respectively. Tracey intertest variability revealed small, statistically significant bias for sphere and MSE (+0.071 D and +0.070 D, p  = 0.011, 0.013). Shin-Nippon reproducibility showed no significant bias.
Conclusions:  Autorefraction measurements captured by both the Tracey and Shin-Nippon devices agree well with subjective refraction. The Shin-Nippon shows lower intratest variability.     

Evaluation of potential visual acuity in eyes with macular oedema secondary to retinal vein occlusion

Purpose:  To evaluate the potential visual acuity (VA) of eyes with macular oedema (MO) associated with retinal vein occlusion (RVO).
Methods:  Thirty-one eyes of 31 patients with MO associated with RVO were examined and then treated with an intravitreal injection of bevacizumab. Of these 31 eyes, 22 showed complete resolution of the MO at 1 month after treatment, at which time potential VA was determined; 12 eyes had good function and 10 had poor function at this time. Optical coherence tomography was used to detect the junctions between inner and outer segments of the photoreceptors (IS/OS) as a hallmark of integrity of the outer photoreceptor layer.
Results:  In the poor function group, pretreatment VA was significantly worse ( P  = 0.0106) and pretreatment central macular thickness was significantly greater ( P  = 0.0121). Preservation of the foveal photoreceptor layer before treatment was associated closely with good visual function after resolution of MO, and IS/OS line beneath the fovea was detected more frequently before treatment in eyes with good function ( P  = 0.0053).
Conclusions:  In eyes with MO associated with RVO, when the IS/OS line was detected beneath the fovea, they would be expected to have good vision after resolution of the MO.     

Cataract surgery in high-risk age-related macular degeneration: a randomized controlled trial

Background:  To investigate if cataract surgery causes progression, from high-risk early age-related macular degeneration (AMD) to choroidal neovascularization (CNV), in the postoperative period.
Methods:  Randomized controlled trial. Patients, with visually significant cataract and fundus features of early AMD at high risk of progression to CNV, were randomized into two groups and were evaluated at baseline and 6 months. The study patients ( n  = 27) underwent immediate cataract surgery. The control group ( n  = 29) comprised patients who had cataract surgery deferred until after the 6-month visit. Assessment included visual acuity, quality of life (QoL) and fundus fluorescein angiography (FFA).
Results:  Of 68 eligible eyes, 60 participated and 56 completed the study. Three referred eyes (3.2%) were ineligible on the basis of a pre-existing, unsuspected occult CNV that was detected by baseline FFA. All three cases had end-stage exudative AMD in the fellow eye. Of the study eyes in the immediate surgery arm ( n  = 27), one (3.7%) developed CNV compared with none (0/29) in the deferred arm (χ²; P  = 1.0) at 6 months. In the operated group, there was a 2.8-line improvement in logMAR visual acuity and 2.1-fold average gain in QoL at 6 months.
Conclusions:  No increased short-term risk of progression of AMD to CNV in high-risk fundi following uncomplicated phacoemulsification surgery was found. A low threshold for performing preoperative imaging in patients with AMD, especially in those with exudative AMD in the fellow eye, to exclude undetected CNV is recommended. Provided there is no CNV, there are distinct benefits of cataract surgery in people with early AMD.     

Customized hydrogel contact lenses for keratoconus incorporating correction for vertical coma aberration

Purpose:  To study the effects on visual performance of a novel custom hydrogel contact lens, which employs a correction for vertical coma aberration, in keratoconic eyes.
Methods:  Six subjects (8 eyes) with mild or moderate keratoconus were recruited for the study. Preliminary measurements included corneal topography, wavefront aberrometry, subjective refraction, visual acuity (VA) and 50% contrast VA. Based on the aberrometry data, customized lenses were made and fitted to the subjects. Evaluation of the on-eye performance of the lenses was carried out, including wavefront aberrometry, over-refraction, VA and 50% contrast VA. In two of the subjects, both eyes were fitted with the customized lenses, and binocular performance was evaluated.
Results:  Monocular visual performance with a 4 mm pupil, with the lenses worn, was improved, and reached the mean values of −0.003 (LogMar units) of 100% high contrast VA, and 0.049 (in LogMar units) of 50% contrast VA. Vertical coma aberration and total higher-order aberrations (HOAs) were reduced (naked eyes: −0.64 ± 0.21 root mean square (rms) of vertical coma and 0.86 ± 0.15 rms of total HOAs; with the lenses worn: −0.29 ± 0.23 rms of vertical coma and 0.57 ± 0.17 rms of total HOAs, all for a 4 mm pupil). Binocular VA results from two of the subjects were on average −0.040 (LogMar units) 100% high contrast acuity and −0.060 (LogMar units) 50% contrast visual acuity.
Conclusions:  Customized hydrogel contact lenses implementing correction of vertical coma, have been found to improve both monocular and binocular visual performance of eyes affected with mild or moderate keratoconus.     

The development of the Quality of Life Impact of Refractive Correction (QIRC) questionnaire

Purpose:  Binocular summation (binocular sensitivity > monocular sensitivity) and binocular inhibition (binocular sensitivity < monocular sensitivity) have been shown in various laboratory and clinical situations. The occurrence of habitual binocular summation/inhibition is unknown. The aim of this study was to investigate binocular performance in 100 'ocularly normal' subjects over the age of 45 years attending an optometric practice. In addition, very little data exist on habitual quality of life (QOL) scores in normal subjects. We aimed to investigate whether binocular performance for different visual tasks affected QOL scores.
Methods:  Right eye, left eye and binocular contrast sensitivity (CS), near and distance logMAR acuity (VA), and face recognition (FR) were measured. Vision-related quality of life (QOL) scores were measured using the standard NEI–VFQ 25 questionnaire.
Results:  Habitual binocular summation ratios were similar to those reported under laboratory conditions. Binocular summation ratios for visual acuity were 26%, 47% for CS and 11% for FR. Binocular inhibition was shown by 12 subjects with VA, seven people in CS and 31 subjects with FR. No significant associations were shown between the summation ratios of distance VA, near VA, CS & FR and the 13 different QOL categories.
Conclusions:  Face recognition showed the poorest summation as it falls under the complex pattern recognition known to produce lower summation under laboratory conditions. Binocular summation ratios were not significantly associated with either the age of the subject or to the differences between the two eyes. The lack of correlation between binocular summation ratios and QOL was because of the high scores shown by the normal subjects.     

Correlation between CFH Y402H and HTRA1 rs11200638 genotype to typical exudative age-related macular degeneration and polypoidal choroidal vasculopathy phenotype in the Japanese population

Background:  Typical exudative age-related macular degeneration (AMD) and polypoidal choroidal vasculopathy (PCV) are two of the major macular diseases found in Asians. Although genomic studies have shown a contribution by CFH and LOC387715/ HTRA1 polymorphisms to the development of these two diseases, the correlation of the clinical phenotypes to these genotypes has not been determined in Asian patients.
Methods:  The prevalence of the CFH Y402H and HTRA1 rs11200638 genotypes was determined in 116 patients with typical exudative AMD and in 204 patients with PCV. Potential correlations of these polymorphisms were tested retrospectively and cross-sectionally for bilaterality of the disease, final visual acuity and the greatest linear dimension of the choroidal neovascular (CNV) lesion.
Results:  There was no significant difference in the incidence of CFH Y402H ( P  = 0.598) and HTRA1 rs11200638 ( P  = 0.290) between eyes with typical exudative AMD and with PCV. There was a significant association between the lesion size and HTRA1 rs11200638. For eyes with typical AMD, the size of the lesion (6363 ± 2837 µm) was significantly larger in the high-risk homozygous group (AA), than in the low-risk homozygous group (GG) (3866 ± 1947 µm; P  = 0.0003). The same tendency was observed for the size of the lesion in PCV cases (homozygous group: 6347 ± 2673 µm, non-risk homozygous group: 4405 ± 2066 µm, P  = 1.3 × 10⁻⁵).
Conclusions:  A common genetic background may exist between typical exudative AMD and PCV patients. Among the patients with these two clinical entities, those with a homozygous HTRA1 rs11200638 risk allele had larger CNV lesions.     

Current trends in photodynamic therapy

Background:  Patients with wet age-related macular disease (AMD) and subfoveal choroidal neovascular membrane (CNV) may be offered photodynamic therapy (PDT). Currently, Visudyne (Verteporfin) is the only photosensitizer approved by the FDA and randomized trials have shown that treatment can prevent severe vision loss. Combination therapy with Visudyne PDT and intravitreal triamcinolone may be additionally beneficial. In an effort to develop a more effective therapy, we have undertaken studies in primates and in patients with advanced AMD using a new photosensitizer, talaporfin sodium. Following dose-ranging work in the normal primate retina, a study in humans investigated the safety and effectiveness of this drug.
Methods:  Eleven patients with vision of <6/60 and persistent leakage from CNV were recruited. Following talaporfin sodium injection of 0.5 mg kg⁻¹ bodyweight, a light dose of between 24 and 48 J cm⁻² was given with a 664 nm laser. Fluorescein angiography and visual acuity (VA) were performed before and after therapy. Adverse events were recorded. Follow-up was for 14 days, but informal review was longer (in some cases ≥ 40 weeks).
Results:  All patients showed evidence of decreased leakage from CNV. No re-opening of closed choroidal vessels was observed during extended follow-up. At the last follow-up, VA was stable in seven patients, improved in three and decreased in one (using >0.1 logMAR). Three adverse events were reported; two related to photosensitivity of the skin and one patient had closure of a branch retinal vein.
Conclusion:  Talaporfin sodium PDT showed extended closure of CNVs and therefore has potential for treating exudative AMD and other choroidal vascular anomalies.     

Components of the fibrinolytic system in the vitreous body in patients with vitreoretinal disorders

Purpose:  To assess components of the fibrinolytic system in the vitreous humour and serum of patients with vitreoretinal disorders.
Methods:  Forty-three samples of vitreous humour and plasma of 43 patients undergoing pars plana vitrectomy for macular hole, macular pucker, retinal detachment or proliferative vitreoretinopathy were evaluated for their content of plasminogen, a₂-antiplasmin, plasminogen-activator-inhibitor 1, plasmin-a₂-antiplasmin-complex, tissue plasminogen activator, total protein, albumin, d-dimer. Patient groups were compared with each other using the U -test (Mann and Whitney) for non-parametric testing of two independent samples.
Results:  The groups of retinal detachment and proliferative vitreoretinopathy had elevated vitreal levels of plasminogen-activator-inhibitor 1 (352.5 and 370.7 ng/mL vs. 1.86 and 56.6 ng/mL, P  = non-significant), plasmin-a₂-antiplasmin-complex (2416.5 and 1836.2 µg/L vs. 124.2 and 133.4 µg/L, P  < 0.001), albumin (0.08 and 0.15 g/dL vs. 0.03 and 0.07 g/dL, P  < 0.05) and d-dimer (4.76 and 1.64 µg/mL vs. 0.40 and 0.48 µg/mL, P  = non-significant) when compared with patients with macular hole and macular pucker.
Conclusions:  There are significant differences in the vitreal concentration of components of the fibrinolytic system in patients with vitreoretinal disorders. Breakdown of the blood–retinal barrier and complex disease-specific mechanisms are thought to be responsible for an increase of components of the fibrinolytic system in the vitreous.     

The effect of micro-incision and small-incision coaxial phaco-emulsification on corneal astigmatism

Purpose:  To evaluate the effect of micro-incision (2.2 mm) and small-incision (2.6 mm or 3.0 mm) coaxial phaco-emulsification on surgically induced astigmatism (SIA).
Methods:  Cataract patients ( n  = 83, 129 eyes) were randomized into three groups: 43 eyes in the 2.2-mm incision group, 42 eyes in the 2.6-mm group and 44 eyes in the 3.0-mm group. Torsional phaco-emulsification was followed by intraocular lens implantation via the Monarch II injector with the C cartridge (Alcon Laboratories Inc., Fort Worth, TX, USA). Corneal astigmatism, SIA and uncorrected distance visual acuity were assessed 30 and 90 days after cataract surgery.
Results:  At 30 and 90 days postoperative, SIA of the 3.0-mm group was greater than SIA of the 2.2-mm and 2.6-mm groups ( P  ≤ 0.015), but SIA was similar between the 2.2-mm group and the 2.6-mm group. Timewise, mean SIA at 30 days was greater than SIA at 90 days in the 3.0-mm group ( P  = 0.04), while SIA did not change with time for the 2.2-mm and 2.6-mm groups. Postoperative uncorrected distance visual acuity tended to be better with the smaller incisions, but this trend did not reach stastical significance ( P  ≥ 0.07).
Conclusion:  Incision size contributed to postoperative corneal astigmatism. When incision size was reduced from 3.0 mm to 2.6 mm, SIA was reduced and refractive stabilization was faster. Reduction of incision size from 2.6 mm to 2.2 mm offered no greater reduction of SIA when using the C cartridge; however, the D cartridge (designed for 2.2-mm incisions) should be evaluated.     

Comparison of VEP with contrast sensitivity and other measurements of central visual function

Purpose: In order to evaluate alternative visual acuity testing techniques, especially to discriminate between small changes and for high visual acuity, we conducted a study covering several state‐of‐the‐art techniques. Methods: In this cross‐sectional study, a homogeneous cohort of healthy and young patients (n = 33; 66 eyes) underwent ETDRS vision acuity (VA) testing, testing for contrast sensitivity (CS), VA determination with spatial frequency sweep visual evoked potentials (VEP) and a series of examinations of perifoveal retinal nerve fibre layer thickness (RNFLT) using Spectralis SD‐OCT. To simulate the effect of artificial media opacity, CS, and VEP were repeated with Bangerter foils. Results: We found that Bangerter foils can be used to reduce VA effectively measured by VA testing and VEP VA. CS correlated significantly with VA (correlation coefficients ranging from 0.54 to 0.77). VEP may be used to estimate VA; nevertheless, we found no significant correlation. RNFLT did not correlate significantly with VA. Conclusion: CS seems to correlate well with VA when used for high VA. All other used examinations seem to have difficulties distinguishing between small differences in VA or when the VA is high.     

Evaluation of retinal nerve fibre layer thickness and visual evoked potentials in optic neuritis associated with multiple sclerosis

Background: The aim was to compare the retinal nerve fibre layer (RNFL) thickness and visual evoked potentials (VEP) among eyes with multiple sclerosis (MS)‐associated optic neuritis, unaffected eyes of the same patients and eyes of disease‐free controls. Changes in RNFL thickness, visual acuity (VA) and VEP over time are evaluated in MS‐associated optic neuritis. Methods: Forty‐six eyes of 23 patients (six male and 17 female), who suffer from MS and were diagnosed with unilateral or bilateral optic neuritis, participated in the study. Forty eyes of 20 age‐ and gender‐matched controls were tested. VA measurement, optical coherence tomography and VEP were performed in all patients at presentation and at one, three and six months thereafter. Results: There was a statistically significant difference in VA between MS eyes with optic neuritis and controls (p < 0.0001), as well as between MS eyes with and without optic neuritis (p < 0.005). VA improved over time. Average RNFL thickness was reduced in MS eyes with or without optic neuritis in comparison to control eyes. This reduction in RNFL thickness was more marked over time. The amplitude of P₁₀₀ was significantly decreased in MS eyes with optic neuritis in comparison to controls (p < 0.0001) and there was a statistically significant delay in peak time of P₁₀₀ in MS eyes with optic neuritis versus the eyes of normal subjects (p < 0.0001), which improved over time. Conclusion: The present study suggests that there is a progressive decrease in RNFL over time in eyes with optic neuritis associated with MS. The amplitude and latency of P₁₀₀ in VEP examination returned to normal ranges over time.     

Objective predictors of subjective visual function for different age‐related cataract morphologies

Purpose:  To find objective chart tests that give a measure of visual function in the different age-related cataract morphological groups and can be applied in a clinical setting.
Methods:  Subjects with age-related cataract ( N  = 33) were recruited to the study from both private optometric practice and a hospital eye department. All subjects underwent LOCS III grading of their cataract and had their functional vision assessed using the VF-14 questionnaire. High (96%) and low (16%) contrast logMAR visual acuity were measured together with Pelli–Robson contrast sensitivity. A stepwise linear regression was then performed on the data to find significant predictors for VF-14 in the three age-related cataract morphological groups as well as in a mixed group.
Results:  Low contrast logMAR visual acuity was a significant predictor of VF-14 in the cortical ( p = 0.014 ) and nuclear ( p = 0.024 ) subgroups. For the mixed morphological group both high and low contrast visual acuity were significant predictors ( p < 0.03 ). There were only three subjects with pure posterior subcapsular cataract and so no meaningful analysis could be performed.
Conclusions:  Low contrast logMAR visual acuity may be a better predictor of visual function in cortical and nuclear cataract compared with high contrast logMAR visual acuity or Pelli–Robson contrast sensitivity.     

The impact of optical factors on resolution acuity in children with Down syndrome

PURPOSE: Down syndrome (DS) is associated with reduced visual acuity that cannot be explained by motivational or attentional factors. To isolate the contribution of optical factors to visual performance in DS, two types of resolution acuity were measured: grating resolution acuity, which is limited by optical quality, and interferometric acuity, which effectively bypasses the optics of the eye. METHODS: Twenty-nine children with DS (age range, 9-16 years) were tested. Sixty-eight age-matched, developmentally healthy children acted as controls. All wore best refractive correction, and none had clinically significant ocular disease. Grating resolution and interferometric acuity were measured according to a two-alternative, forced-choice procedure. RESULTS: There was no change in grating resolution acuity or interferometric acuity with age in either group. Mean grating resolution acuities were -0.12 log of the minimum angle of resolution (logMAR; SD +/- 0.07) for the control group and +0.48 logMAR (SD +/- 0.09) for the DS group. Mean interferometric acuities were -0.11 logMAR (SD +/- 0.08) for the control group and +0.004 (SD +/- 0.06) for the DS group. In the DS group, the mean interferometric acuity was reduced by a factor of 1.3, whereas mean grating resolution acuity was substantially reduced, by a factor of 4.1, compared with controls. CONCLUSIONS: Grating resolution and interferometric thresholds are reduced in children with DS. However the discrepancy between developmentally healthy children and those with DS is greater for grating resolution acuity, suggesting that degradation in optical quality is a major contributor to poor visual performance in children with DS.     

Long-term visual and microperimetry outcomes following autologous retinal pigment epithelium choroid graft for neovascular age-related macular degeneration

Background:  To describe the 2- to 4-year visual and microperimetry outcomes of autologous retinal pigment epithelium (RPE)-choroid graft in patients with neovascular age-related macular degeneration (AMD).
Methods:  In this retrospective cohort study, 12 patients with subfoveal neovascular AMD who had undergone autologous RPE-choroid graft between August 2004 and June 2005 were reviewed. Change in visual acuity (VA), contrast sensitivity (CS), fixation stability and retinal sensitivity on microperimetry after 2–3 years and the rates of late postoperative complications were examined.
Results:  Patients were followed for 26–48 months (mean, 39). Median preoperative VA (logMAR) was 0.87 but declined to 1.43 (1 year), 1.46 (2 years) and 1.38 (3 years), P  = 0.001. Median CS (logCS) was 0.75 preoperatively but declined to 0.45 at 2 years. Six patients had serial microperimetry. Fixation stability declined in 1 but improved in 2 patients. All 6 had decline in retinal sensitivity over the graft during follow up. Retinal detachment did not occur after 12 months but 8 developed epiretinal membrane, 12 had cystic retinal change over the graft and 4 developed recurrent choroidal neovascularization. However, 10 grafts retained autofluorescence signal at 18–48 months of follow up.
Conclusions:  Autologous RPE-choroid graft can maintain VA, stable fixation and retinal sensitivity in some patients for over 3 years. The spatial correlation between graft autofluorescence, outer retinal structures on optical coherence tomography and retinal sensitivity are consistent with photoreceptor cell rescue. However, we caution the use of this technique as there is high complication rate and delayed loss of retinal function.     

Subthreshold transpupillary thermotherapy in Chinese patients with myopic choroidal neovascularization: one- and two-year follow up

Background:  To perform a safety and efficacy study of subthreshold transpupillary thermotherapy (TTT) in Chinese patients with choroidal neovascularization (CNV) secondary to pathologic myopia.
Methods:  In a prospective study, patients with subfoveal or juxtafoveal CNV secondary to high myopia underwent subthrehold TTT with fixed treatment and follow-up protocols. From October 2002 to July 2005, 12 and 24 months of follow up were completed for 21 eyes and 13 eyes respectively.
Results:  The mean best-corrected visual acuities (BCVA) were maintained at the baseline level at 1 and 2 years. Seventy-two per cent of eyes and 63% of eyes had stable or improved BCVA at 12 and 24 months. Thirty-four per cent and 39% of eyes had a moderate gain in vision (improved by three or more lines) at 12 and 24 months respectively. The average number of subthreshold TTT treatments was 1.7. The major complication of subthreshold TTT included laser-related low-grade retinal pigment epithelium atrophy in two eyes of young patients with clear lenses. The final VA was significantly associated with pretreated VA ( r  = 0.614, P  = 0.003). The final VA improvement was significantly associated with pretreatment VA in negative correlation ( r  = −0.731, P  = 0.0002, Person correlation test).
Conclusions:  Subthreshold TTT in Chinese patients with pathologic myopia and subfoveal or juxtafoveal CNV generally maintained vision at 1- and 2-year follow up. Using decreased power of subthreshold TTT, especially in the younger patients with a clear lens, is suggested.     

Spatial vision deficits in infants and children with Down syndrome

PURPOSE: Infants and children with Down syndrome show reduced visual acuity and contrast sensitivity when tested with conventional behavioral techniques. These results may reflect sensory deficits of optical or neural origin or a loss of performance in mechanisms responsible for generating the behavioral response. The purpose of this study was to compare objective acuity and contrast sensitivity measurements recorded with visual-evoked potentials (VEPs), with behavioral clinical test results in a group of children with Down syndrome and a group of control subjects. The goal was to determine whether children with Down syndrome still have a sensory deficit when tested using a procedure that is less cognitively demanding than conventional tests. METHODS: The subject group comprised 58 children with Down syndrome and 44 control subjects, aged 3 months to 14.15 years. Visual acuity and contrast sensitivity were measured with steady state, swept VEPs and behavioral techniques. VEP acuity was obtained from 36 children with Down syndrome and 40 control subjects, and behavioral acuity from 54 children with Down syndrome and 35 control subjects. VEP contrast sensitivity was measured in 24 children with Down syndrome and 34 control subjects, and behavioral contrast sensitivity in 42 children with Down syndrome and 25 control subjects. Group differences in visual acuity and contrast sensitivity were analyzed with an analysis of covariance (ANCOVA), with age as a covariate. RESULTS: Visual acuity thresholds were significantly lower in the group with Down syndrome than in the control group. This was true for both VEP (P < 0.01) and behavioral measures (P < 0.01). The Down syndrome group also had reduced contrast sensitivity when compared with the control subjects, for VEP contrast sensitivity (P < 0.01) and behavioral contrast sensitivity (P < 0.01). The group differences remained when children with ophthalmic anomalies were excluded from the analysis. CONCLUSIONS: The reduced visual acuity and contrast sensitivity in the Down syndrome group support the idea of an underlying sensory deficit in the visual system in Down syndrome.     

What can this child see? Practical interpretation of visual acuity (VA) measures for parents and teachers of visually impaired children

Introduction:  Many children with developmental disabilities have associated visual impairment. Families and others working with children need to understand their visual abilities and limitations to ensure that material presented to them is easily visible.
Purpose:  To develop a web-based system for displaying and printing high contrast picture and letter images relating to a range of visual acuity (VA) levels.
Methods:  A series of web pages were designed and uploaded to http://www.science.ulst.ac.uk/visionsci/links.htm . Images from the LogMAR acuity test and pictures from the Kay Picture test describing VAs from 6/480–6/12 (for 0.3–3 m working distances) are included.
Results:  Images can be downloaded at threshold level and well above threshold for a range of VAs and a variety of working distances. The importance of working well above threshold is stressed. These images are included in reports sent out from a multi-disciplinary visual assessment clinic at the Royal Victoria Hospital, Belfast. Audit of families, education and health professionals receiving reports support the utility of this information.
Discussion:  The importance of vision in early learning is known. Children with developmental disability must receive early, thorough visual assessment and information gained disseminated in appropriate format to those working with the child (including family). An important part of this is meaningful interpretation of VA data that can be related to the size and complexity of educational and recreational material. Feedback from our clinical work suggests that examples of appropriately sized material for children with varying levels of VA is valued.
Conclusions:  The availability of free downloadable examples of appropriately sized images provides a useful tool for those working with the visually impaired, particularly where communication is problematic.     

Visual acuity in unilateral cataract.

BACKGROUND: Patching the fellow eye in infancy is a well recognised therapy to encourage visual development in the lensectomised eye in cases of unilateral congenital cataract. The possibility of iatrogenic deficits of the fellow eye was investigated by comparing the vision of these patients with untreated unilateral patients and binocularly normal controls. METHODS: Sweep visual evoked potentials (VEPs) offer a rapid and objective method for estimating grating acuity. Sweep VEPs were used to estimate acuity in 12 children aged between 4 and 16 years who had had a congenital cataract removed in the first 13 weeks of life. The acuities of aphakic and fellow phakic eye were compared with the monocular acuities of similarly aged children who have good binocular vision, and with children with severe untreated uniocular visual impairment. Recognition linear acuities were measured with a linear Bailey-Lovie logMAR chart and compared with the sweep VEP estimates. RESULTS: A significant difference was found between Bailey-Lovie acuity of the fellow eye of the patient group and the right eye of binocular controls, and the good eye of uniocular impaired patients (one way ANOVA, p < 0.01). However, this was not evident for a similar comparison with sweep VEP estimates. There was no significant difference between the right and left eye acuities in binocular controls measured by the two techniques (paired t test). CONCLUSION: A loss of recognition acuity in the fellow phakic eye of patients treated for unilateral congenital cataract has been demonstrated with a logMAR chart. This loss was not apparent in children who have severe untreated uniocular visual impairment and may therefore be an iatrogenic effect of occlusion. An acuity loss was not apparent in the patient group using the sweep VEP method. Sweep VEP techniques have a place for objectively studying acuity in infants and in those whose communication difficulties preclude other forms of behavioural test. The mean sweep VEP acuity for the control groups is 20 cpd--that is, about 6/9. When acuities higher than this are under investigation--for example, in older children, slower transient VEP recording may be more appropriate, because higher spatial frequency patterns are not as visible at higher temporal rates (for example, 8 Hz used in sweep VEP recordings).     

Pulsatile ocular blood flow measurements in healthy Asian eyes: reference values for an Indian population

Purpose:  To investigate pulsatile ocular blood flow (POBF) in a healthy Indian population and use the data derived as reference values.
Methods:  Two hundred and fifty-two healthy subjects (121 males, 131 females) underwent intraocular pressure and POBF measurement with the Ocular Blood Flow Analyzer (Paradigm Medical Industries, Salt Lake City, UT, USA and formerly the POBF Tonograph). Before POBF measurement, subjects underwent a complete ophthalmic examination including refraction, slitlamp examination and biomicroscopic fundoscopy and Goldmann applanation tonometry (GAT). Subjects with ocular pathology were excluded from the study. Median age was 29 years (male median 32 years, female median 27 years).
Results:  Average POBF in males was found to be 1052 µL min⁻¹ (95% CI: 988–1116 µL min⁻¹) and in females to be 1293 µL min⁻¹ (95% CI: 1222–1364 µL min⁻¹). Median age was significantly different between males and females (Mann–Whitney U  = 6685; p  = 0.0311) but POBF was found to be independent of age in both sexes. As a group, mean refractive error influenced POBF (Kendall's τ = 0.24; p  = 0.0017).
Conclusions:  Pulsatile ocular blood flow values in Indians appear to be higher than reported in studies conducted on other racial groups. The reasons for this difference could be instrumental or anatomical (i.e axial length, ocular rigidity). Care should be taken in deriving normative data using the Ocular Blood Flow Analyzer in mixed race groups.