Optotype Test Research Articles

Visual results and subjective satisfaction after implantation of two different trifocal diffractive intraocular lenses models (AcrySof IQ PanOptix and AT LISA tri 839 MP).

This study aimed to compare visual results following the implantation of two distinct diffractive trifocal IOLs utilizing various vision evaluation techniques and subjective satisfaction. The study included 32 eyes receiving AcrySof IQ PanOptix implantation and 32 receiving AT LISA tri 839 MP. Post-operative examination at one year included uncorrected visual acuity (UCVA), distance-corrected visual acuity (DCVA) at 4 m, 80 cm, 60 cm, and 40 cm, Contrast sensitivity under photopic and mesopic conditions, and a questionnaire on subjective quality of vision, optical phenomena, and spectacle independence. The two groups were similar in baseline demographics, pre-operative visual, biometric data (except for axial length), and surgical paraments. The PanOptix outperformed the AT LISA tri in the intermediate range when using the standard visual acuity testing (UCVA: 0.23 ± 0.14 logMAR vs. 0.31 ± 0.17 logMAR, p = 0.04; BCVA: 0.21 ± 0.12 vs. 0.28 ± 0.14, p = 0.03) and in the intermediate and far range when using the interactive computer program (intermediate: UNVA "E" optotype test: 0.05 ± 0.12 vs. 0.12 ± 0.13, p = 0.03; Far: UNVA "E" optotype: 0.07 ± 0.12 vs. 0.13 ± 0.10, p = 0.05). In addition, the PanOptix group had higher contrast sensitivity under photopic and mesopic conditions with and without glare at all spatial frequencies. There was no difference in subjective outcomes between the groups. Patients who received PanOptix IOL had better visual outcomes for intermediate and far with higher contrast sensitivity under various conditions. Based on patients ' needs and demands, these results could support discussion when tailoring the optimal multifocal IOl.

Can children measure their own vision? A comparison of three new contrast sensitivity tests.

To investigate the feasibility of children measuring their own contrast sensitivity using a range of tablet- and paper-based tests. Forty children aged 5-15 years with amblyopia (N = 10), bilateral vision impairment (N = 10) or good vision (N = 20) measured their own vision on a screen-based optotype test (Manifold), a gamified vision test (PopCSF) and a paper-based test (Spotchecks) in a laboratory with minimal supervision. Completion rate, test-retest repeatability, test duration and participants' preferences were recorded for each test. Most participants (36/40) were able to perform all three tests. All tests were correlated with clinically measured visual acuity and contrast sensitivity (p < 0.001). The 95% coefficient of repeatability was 0.30 dB for Manifold, 0.29 dB for PopCSF and 0.13 dB for Spotchecks. All tests differentiated between children with reduced contrast sensitivity and control participants. PopCSF and Spotchecks were also able to differentiate between children with amblyopia and those with good vision. Median test time was 152, 130 and 202 s for Manifold, PopCSF and Spotchecks, respectively. Twenty-two participants preferred the PopCSF test, 10 preferred Spotchecks and 6 preferred Manifold. Thirty-nine out of the 40 children (98%) said they would measure their own vision at home using at least one of these tests every month. Children and young people can test their own contrast sensitivity with repeatable results. Of these three tests, the most repeatable was Spotchecks, the quickest was PopCSF and participants' favourite was PopCSF. Nearly all of the participants said they would be willing to use at least one of the three tests at home.

Grating visual acuity impairment assessed by sweep visually evoked potentials in children with optic pathway tumors unable to perform optotype acuity tests.

To determine visual impairment due to optic pathway tumors in children unable to perform recognition acuity tests. Grating visual acuity scores, in logMAR, were obtained by sweep visually evoked potentials (SVEP) in children with optic pathway tumors. The binocular grating visual acuity deficit was calculated by comparison with age-based norms and then assigned to categories of visual impairment as mild (from 0.10 to 0.39 logMAR), moderate (from 0.40 to 0.79 logMAR), or severe (≥0.80 logMAR). Interocular differences were calculated by subtraction and considered increased if >0.10 logMAR. The participants were 25 children (13 boys; mean ± SD age, 35.1 ± 25.9 months; median age, 32.0 months) with optic pathway tumors (24 gliomas and 1 embryonal tumor), mostly located at the hypothalamic-chiasmatic transition (n=21; 84.0%) with visual abnormalities reported by parents (n=17; 68.0%). The mean grating acuity deficit was 0.60 ± 0.36 logMAR (median, 0.56 logMAR). Visual impairment was detected in all cases and was classified as mild in 10 (40.0%), moderate in 8 (32.0%), and severe in 7 (28.0%) children, along with increased interocular differences (>0.1 logMAR) (n=16; 64.0%). The remarkable ophthalmological abnormalities were nystagmus (n=17; 68.0%), optic disc cupping and/or pallor (n=13; 52.0%), strabismus (n=12; 48.0%), and poor visual behavior (n=9; 36.0%). In children with optic pathway tumors who were unable to perform recognition acuity tests, it was possible to quantify visual impairment by sweep-visually evoked potentials and to evaluate interocular differences in acuity. The severity of age-based grating visual acuity deficit and interocular differences was in accordance with ophthalmological abnormalities and neuroimaging results. Grating visual acuity deficit is useful for characterizing visual status in children with optic pathway tumors and for supporting neuro-oncologic management.

Clinical usefulness of the teller acuity cards test in preliterate children and its correlation with optotype test: A retrospective study

This study evaluated the reproducibility of the Teller Acuity Cards (TAC) test, its correlation with the optotype test, and its usefulness for detecting amblyopia in preliterate children. We retrospectively reviewed the medical records of 64 children who had undergone the TAC test more than once and were later followed up with the optotype test. The mean corrected visual acuities (logMAR) of the first and last TAC tests were 0.86 (mean 19.9 months) and 0.69 (27.7 months), respectively. The first optotype acuity was 0.18 (33.7 months). The first TAC acuity result was positively correlated with the age of the child, but it was not statistically significant (r = −0.077, p > 0.05). The first and last TAC test acuities were significantly correlated (r = 0.382, p < 0.01). There was a significant but small correlation between the final TAC and the first optotype acuities (r = 0.193, p < 0.05). Interocular differences in visual acuity were significantly correlated between the last TAC and first optotype tests (r = 0.395, p < 0.05). TAC acuity might be a valid predictor of optotype acuity later on although it was underestimated compared to that in the optotype test. The TAC test can be used to detect unilateral amblyopia in preliterate children.

Spherical power error evaluation and stereopsis by using holographic optotype tests

Two holographic optotypes have been designed and fabricated using polyvinyl alcohol/acrylamide photopolymer in order to measure visual acuity and stereopsis. One of them was a multivergence target for subjective measurements to determine the spherical refractive error of the human eye in the range −5 to +4 diopters (D) in a single step. The amplitude of accommodation is determined at the same time. The second one was a stereopsis test with an embossed picture to determine the degree of stereoscopic difficulties.

Predicting individual contrast sensitivity functions from acuity and letter contrast sensitivity measurements.

Contrast sensitivity (CS) is widely used as a measure of visual function in both basic research and clinical evaluation. There is conflicting evidence on the extent to which measuring the full contrast sensitivity function (CSF) offers more functionally relevant information than a single measurement from an optotype CS test, such as the Pelli–Robson chart. Here we examine the relationship between functional CSF parameters and other measures of visual function, and establish a framework for predicting individual CSFs with effectively a zero-parameter model that shifts a standard-shaped template CSF horizontally and vertically according to independent measurements of high contrast acuity and letter CS, respectively. This method was evaluated for three different CSF tests: a chart test (CSV-1000), a computerized sine-wave test (M&S Sine Test), and a recently developed adaptive test (quick CSF). Subjects were 43 individuals with healthy vision or impairment too mild to be considered low vision (acuity range of −0.3 to 0.34 logMAR). While each test demands a slightly different normative template, results show that individual subject CSFs can be predicted with roughly the same precision as test–retest repeatability, confirming that individuals predominantly differ in terms of peak CS and peak spatial frequency. In fact, these parameters were sufficiently related to empirical measurements of acuity and letter CS to permit accurate estimation of the entire CSF of any individual with a deterministic model (zero free parameters). These results demonstrate that in many cases, measuring the full CSF may provide little additional information beyond letter acuity and contrast sensitivity.

Pacific Acuity Test

The Pacific Acuity Test (PAT) is a new vanishing optotype test designed to measure recognition visual acuities in preverbal children using a face and opposing oval figure in a forced-choice preferential looking format. This study evaluates the testability, validity, and interobserver reliability of the PAT. Fifty-two subjects, aged 6 to 36 months, were tested by a primary observer to determine both recognition and resolution visual acuities using the PAT. Subjects were also tested using the Cardiff Acuity Test (CAT) to provide comparative resolution acuities. Two additional observers independently evaluated video-recorded subject responses for testability and interobserver reliability analysis. An independent grader determined acuity thresholds from each observer's observations, and a logistic regression model was used for additional analysis of acuity thresholds, validity, and testability. Forty-seven of 52 subjects completed testing to obtain visual acuities with the PAT. Sixty-nine percent of subjects followed the desired forced-choice strategy to yield recognition acuities with the PAT. Testability for children younger than 18 months was 44%, whereas 96% of children 18 months and older responded to the recognition testing format. Testability for resolution acuity was 92% and 98% for the PAT and CAT, respectively. The mean difference between PAT recognition and CAT resolution acuity thresholds (PAT-CAT) was +0.11 logMAR (0.15 SD, p < 0.001). The observers were in agreement as determined by intraclass correlation coefficients of 0.90 for both PAT recognition and the CAT. High testability and valid recognition acuity measures were achieved using the PAT with children by approximately 18 months of age. The recognition acuities obtained with the PAT were higher, particularly for younger subjects, than comparative resolution acuities found with both the PAT and CAT. Interobserver reliability of observers was the same between the PAT and the CAT.

Rapid Assessment of Neurovisual Integrity Using Multiple Rarebits

Rapid assessments of vision commonly rely on visual acuity testing alone. Although well suited for uncovering optical defects, visual acuity tests may fail to detect dysfunction of the neural substrate. There is a need for a rapid companion test sensitive to neural damage. Evaluation of diagnostic tests. Forty-seven patients with optic nerve or visual pathway lesions of low to moderate severities and 30 normal subjects. A new computer-based quick test of neurovisual integrity was developed using segmented digits defined by rarebits, that is, receptive field-size bright dots briefly presented on a dark background. The test variable was the number of rarebits per segment; digit size was fixed. The test task was to call out verbally all digits that were seen during an 8-second presentation sequence. Test outcomes were contrasted with the results of an optotype acuity test and automated perimetry. All subjects easily grasped the test task. The normal subjects read, on average, 5.6 (± 0.5 standard deviation) of the 6 digits contained in the test sequence, whereas the patients averaged 3.3 ± 1.8 digits. The numbers of digits read correlated modestly with the acuity and perimetry results. Analysis of receiver operating characteristic curves indicated that the multiple rarebit test provided the best discrimination. The multiple rarebit test seemed to be highly capable of detecting neurovisual dysfunction. Its simplicity and uniquely short duration indicate a useful role in screening settings. The test is available free on the Internet. Proprietary or commercial disclosure may be found after the references.

Crowding in Children's Visual Acuity Tests—Effect of Test Design and Age

The aim of this study was to investigate the effect of test design (crowding) and age on visual acuity in a sample of young children. Vision was measured in 103 children aged between 4 and 9 years using five different visual acuity tests. The tests included three crowded tests: logMAR Crowded test, the Sonksen logMAR test, and the Crowded Kay Picture test, and two single optotype tests: the Single Kay Picture and Sheridan Gardiner tests. Tests were presented in a random order using standardized instructions and a defined end-point. Results were analyzed in two age groups, younger (4 to 6 years) and older (7 to 9 years). In both groups, there was a significant main effect of test on acuity (younger: F = 63.92, dF = 4, p < 0.001; older: F = 63.59, dF = 4, p < 0.001). In the younger group, an effect of crowding was seen in all three crowded tests, but in the older group, an effect of crowding was seen only in the crowded letter tests. In both groups, mean acuity was lowest with the logMAR Crowded test, which has the closest interoptotype spacing (0.5), slightly higher with the Sonksen test (with interoptotype spacing of 1.0) and highest with the single optotype tests (no crowding). More crowding was seen in the younger children. Our results show that maturation of line acuity is still taking place between the ages of 4 and 9 years. Measured acuity is affected by the amount of contour interaction induced by the type of optotype (letter or picture) and by the interoptotype separation. Another factor, probably a maturation of gaze control or selective attention is responsible for the reduction in crowding with age.

Comparing a traditional single optotype visual acuity test with a computer-based visual acuity test for childhood amblyopia vision screening: a pilot study

Objective: To investigate the effectiveness of a traditional flip-chart optotype test, the Sheridan Gardiner test (SGT), in measuring visual acuity and detecting amblyopia, compared with a free, computer-based test (CBT), LazyeyeTest.org. Design: Prospective, masked, cross-over study. Participants: Seventy kindergarten-aged children from a downtown Toronto elementary school enrolled in the Kids2See vision screening program. Methods: Visual acuity in the children was measured monocularly using both tests. The visual acuity results, number of referrals, and outcomes of referrals were compared, as was the usability from the perspective of the child and the vision screener. Results: The children were more likely to score low visual acuity values with the CBT, a result predicted by the existence of crowding bars on the CBT's optotypes. The CBT referred an extra 5 children than the SGT, and of the 4 who saw an ophthalmologist 2 had amblyopia. The SGT referred one child not referred by the CBT. The Cohen's kappa coefficient was 0.67 and the difference in referral rates was not significant ( p = 0.13). Relative to the SGT, the sensitivity of the CBT was 88%, specificity was 92%, positive predictive value was 58%, and negative predictive value was 98%. The CBT appeared to be easier and more efficient to administer, more stimulating, and was preferred by the children. Conclusions: Replacing the SGT with LazyeyeTest.org would increase the efficiency and likely the sensitivity of amblyopia screening. Further research is warranted to confirm the outcomes and to determine if the CBT can be administered accurately by lay screeners.

Detecção de ambliopia, ametropias e fatores ambliogênicos em comunidade assistida por Programa da Saúde da Família no Rio de Janeiro, Brasil

OBJETIVOS: Determinar a prevalencia dos fatores ambliogenicos e ambliopia na area adscrita do Programa Saude da Familia (PSF) da Lapa (RJ) e, estimar na mesma area a sensibilidade e especificidade entre metodos de medida de acuidade visual (tabelas ETDRS e LEA) em criancas pre-escolares. METODOS: Estudo transversal de 93 criancas entre tres a seis anos da area adscrita do PSF Lapa, RJ. Todas as criancas foram submetidas a avaliacao oftalmologica completa que incluiu: anamnese dirigida, ectoscopia, medida da acuidade visual com tabela de ETDRS e LEA de forma duplo cega, reflexo vermelho, teste de Titmus, refracao objetiva sob cicloplegia, refracao subjetiva, avaliacao da motilidade ocular, biomicroscopia do segmento anterior, fundoscopia sob midriase. Os dados foram coletados na Policlinica Ronaldo Gazolla, da Universidade Estacio de Sa. RESULTADOS: A prevalencia dos fatores ambliogenicos foi encontrada e distribuida em: 8,4 % de estrabismo; 11,86% de anisometropia e 15,2% de ametropia. O teste de acuidade visual ETDRS apresentou sensibilidade de 100% e especificidade de 18% para deteccao de ambliopia. O teste de acuidade visual LEA apresentou sensibilidade de 100% e especificidade de 30,9% para deteccao de ambliopia. CONCLUSAO: Ambas tabelas ETDRS e LEA podem ser usadas para a triagem de ambliopia porque tiveram 100% de sensibilidade. A especificidade foi maior para a tabela LEA. Porem ainda em nivel baixo. Portanto, ha necessidade da complementacao com o exame oftalmologico completo para confirmar e ratificar a presenca de fatores ambliogenicos em pacientes triados positivamente. A triagem visual feita pelos Agentes Comunitarios de Saude pode identificar criancas com disturbios visuais, referenciando para exame oftalmologico completo; em um grupo etario onde a resolucao dos problemas visuais se apresenta como prioridade. O Programa de Saude da Familia pode ser utilizado para avaliar o estado de visao das criancas brasileiras e seria util que essa avaliacao fosse um marcador estatistico do SUS.

VEP Vernier, VEP Grating, and Behavioral Grating Acuity in Patients with Cortical Visual Impairment

Cortical visual impairment (CVI) is a leading cause of bilateral vision impairment. Because many patients with CVI cannot perform an optotype test, their acuity is often measured with a grating stimulus using a preferential looking (PL) test or the visual-evoked potential (VEP) recording. The purpose of this study is to determine the relationship among VEP vernier acuity, VEP grating acuity, and behavioral grating acuity in patients with CVI. Sweep VEP vernier acuity, sweep VEP grating acuity, and behavioral grating acuity (measured with PL cards) were measured in 29 patients with CVI. The patients ranged in age from 3.2 to 22.7 years (mean: 12.3; SD: 5.3). Because the measures of vernier acuity and grating acuity have different units, the results were expressed as the log deficit (with normal being 30 cycles per degrees and 0.5 arc min, respectively). VEP grating acuity loss and VEP vernier acuity loss were significantly related (r = 0.70) with a slope of 1.31, indicating that indicating that on average, vernier acuity showed a 0.2 log unit deficit compared with VEP grating acuity. Behavioral grating acuity loss and VEP grating acuity loss were also significantly related (r = 0.64) with a slope of 1.55, indicating that behavioral acuity was more reduced (by approximately 0.3 log unit). VEP vernier acuity loss and behavioral grating acuity loss were significantly related (r = 0.66) with a slope of 0.85, indicating that behavioral acuity and VEP vernier acuity showed a similar magnitude of reduction. A Bland-Altman comparison between the VEP vernier acuity method and the behavioral acuity method showed a flat slope (0.30), indicating that the two measures produce similar visual acuity measures across the range of acuity levels. In patients with CVI, VEP vernier acuity showed greater deficits than VEP grating acuity and was more similar to the behavioral measures of grating acuity.

Computer-Based Test to Measure Optimal Visual Acuity in Age-Related Macular Degeneration

The authors present a computer-based method for evaluating the visual acuity of patients with age-related macular degeneration (AMD). It incorporates four features known to improve visual acuity: high contrast, white optotypes on a black background to reduce intraocular scatter, proportional layout to reduce the effects of crowding, and multiple optotypes to minimize the effects of fixation instability and to maximize the likelihood of optotype detection. Experiment 1 evaluated the best-eye acuity of 24 patients with AMD using the ETDRS chart and three versions of the Tumbling E acuity test: multiple black optotypes on a white background, single white optotype on a black background, and multiple white optotypes on a black background. Experiment 2 compared the two White E optotype tests with the ETDRS in patients with AMD, and Experiment 3 measured probability summation in persons with normal vision. Multiple white optotypes on a black background yielded the highest acuity estimates and the ETDRS the lowest. The Single E test yielded a lower estimate of acuity than the two Multiple E tests. The effect of polarity-white on black was better than black on white-was consistent with results found in persons with healthy retinas. For patients with AMD, acuity measured with the Multiple E test was independent of that measured with the ETDRS, but acuity measured with the Single E test decreased as acuity worsened. For the participants with normal vision, the differences between the Multiple and Single E tests were within the known limits of test-retest variability. The multiple-optotype, reversed-polarity test provides a measure of the optimal visual acuity of which a person is capable and, in this sense, may be a useful tool for assessing rehabilitation progress.

Acuity measurements in adult subjects using a preferential looking test

Preferential looking (PL), as a technique for assessing visual acuity, was designed for use with young infants. There are occasions when a practitioner may need to use a PL test with an adult who is unable to participate in acuity measures with conventional optotype tests (such as an adult with learning disabilities, stroke damage or dementia). In preparation for the development of an adult-appropriate PL test, this study compared scores with the Cardiff Acuity Test (CAT, which was designed as a PL test) and a standard LogMAR-based test, the Lea chart. One hundred and one adults with learning disabilities, attending vision screening at Special Olympics, took part in acuity measures with both tests. Athletes subsequently found to have uncorrected refractive errors were excluded and analysis was confined to 72 athletes. There was no significant difference in mean acuity with the two tests, but CAT tended to overestimate scores for poorer acuities. CAT was less sensitive than the Lea chart to interocular acuity differences. Although CAT may be a successful way to assess acuity in patients unable to participate in conventional acuity tests, the practitioner should be cautious in interpreting results. There is the potential with CAT to overestimate acuity and to miss small interocular differences, so criteria for determining 'abnormality' may need to be adjusted.

Binocular interactions in patients with age-related macular degeneration: Acuity summation and rivalry

This study examined two aspects of binocular function in patients with age-related macular degeneration (AMD): summation/inhibition of visual acuity and rivalry. The performance of 17 patients with AMD was compared with that of 17 elderly controls and 21 young people. Monocular and binocular acuities were measured using a multiple-E optotype test. Binocular ratios, defined as the better-eye acuity divided by the binocular acuity, were calculated. We also measured eye dominance during rivalry (proportion of time the participants reported perceiving the input to each eye) and rivalry rates (number of alternations per minute). The results showed that while overall binocular ratios were similar for the three groups, the frequency distributions of people who experienced inhibition, equality or summation were different for the young and AMD groups. In the rivalry test, patients experienced more piecemeal perception than the elderly and young controls, but time dominance from the better-seeing eye was comparable for the three groups. Rivalry rates decreased with age and further with pathology. Moreover, rivalry time dominance of the worse-seeing eye was negatively correlated with interocular acuity differences for the AMD group.

Visual acuity and contrast sensitivity measurements after experimental triethylamine exposures

Objective: The objective was to define the dose-response for triethylamine (TEA) vapour-induced visual changes. Methods: Four core makers were exposed in a dynamically-controlled whole-body chamber to TEA for 4 h at the concentrations of 40.6, 6.5 and 3.0 mg/m3. Before and after the exposure binocular visual acuity and contrast sensitivity at 2.5% contrast were measured. The visual measurements were carried out with the use of optotype test charts (Precision Vision, Villa Park, Ill. USA). The outcome was determined as a change in the rows of the test chart. Results: Visual acuity decreased in three of the four subjects after 40.6 mg/m3 TEA exposure, and remained at the pre-exposure level after 6.5 and 3.0 mg/m3 exposures. Contrast sensitivity at 2.5% contrast decreased in the same three subjects after 40.6 and 6.5 mg/m3 TEA exposures but remained at the pre-exposure level in all subjects after the TEA exposure of 3.0 mg/m3. Conclusions: TEA exposure over 4 h at the concentration of 3.0 mg/m3 in air caused no changes in contrast sensitivity. A corresponding exposure at the concentration of 6.5 mg/m3 caused deterioration in contrast sensitivity in most subjects. Because the blurring of vision occurs within 4 h after the start of working with TEA the results can probably be applied for the setting of an 8 h occupational exposure limit. Moreover, the results are consistent with the current 4.1 mg/m3 ACGIH TLV.

Preschool vision screening: negative predictive value for amblyopia

BACKGROUND/AIMSSingle optotype tests of visual acuity are widely used for preschool vision screening in order to optimise cooperation with testing. These tests may, however, underestimate the visual acuity deficit in...

Screening for amblyopia: a comparison of paediatric letter tests

AIMS/BACKGROUNDThe measurement of visual acuity is the most widely accepted indicator of amblyopia and is thought by some to be the only effective screening test. The aim of this study...

A comparison between different contrast sensitivity tests in the detection of amblyopia

Twenty adult patients with strabismic amblyopia were examined with seven different contrast sensitivity tests in order to determine which of these tests is the most sensitive in the detection of amblyopia. Both grating tests (Vistech, Arden, Cadwell, and Cambridge) and optotype tests (LH, Regan, and Pelli-Robson) were used. The following parameters of the contrast sensitivity function (CSF) were measured: maximum contrast sensitivity, total area of CSF and the area of 8 different spatial frequency bands in the CSF. Based on non-parametric tests, it was found that separations of the normal from the amblyopic eye by means of CSF could be done with:- maximum contrast sensitivity using the Vistech test;- total CSF area using all tests except the Cadwell test;- area of frequency bands (within 1–16 cycles per degree) using Vistech, Pelli-Robson, and the Arden tests;- maximum spatial frequency for tests with a fixed contrast using the LH and Regan tests.

EVALUATION OF THE SONKSEN PICTURE TEST FOR DETECTION OF MINOR VISUAL PROBLEMS IN THE SURVEILLANCE OF‘ PRESCHOOL CHILDREN

The Sonksen Picture Test (SPT) for surveillance of vision in preschool children was evaluated in 842 children, aged 21 to 60 months, from nine health districts in England, Wales and Scotland. The failures and controls were refracted and examined for squint; the Sheridan-Gardiner seven-letter chart (SGLC) was also used with children of > or = 42 months. The SPT was quicker to administer than the SGLC, with median times of one and five minutes, respectively. 98 per cent of children of all ages completed the SPT, whereas 10 per cent of those over 42 months were unable to complete the SGLC. The test method that has been established is developmentally appropriate for this age-group, more so than optotype tests. It is a binocular test that is quick, cheap and simple to administer, and is available to children under five years.