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The differing impact of induced astigmatic blur on crowded and uncrowded paediatric visual acuity chart results
Author(s) -
Little Julie Anne,
Molloy Jaclyn,
Saunders Kathryn J
Publication year - 2012
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/j.1475-1313.2012.00939.x
Subject(s) - astigmatism , emmetropia , visual acuity , optometry , refractive error , snellen chart , medicine , ophthalmology , chart , optics , physics , mathematics , statistics
Purpose Vision screening programs often rely on acuity measures to detect significant refractive error and clinicians use measures of acuity to monitor refractive treatment. This study investigated the effects of induced astigmatism on visual acuity ( VA ) using several paediatric acuity tests: the K eeler Log MAR crowded and single letter acuity tests, the single letter S heridan G ardiner chart, and the crowded and single K ay picture tests. Methods Six fully‐corrected emmetropic adults had induced astigmatic blur imposed at different axes of astigmatism (90°, 180°, 135°, 45°). Astigmatic errors ranged from 0.75 to 3.50 DC. Monocular VA was measured with induced astigmatic blur for each acuity test. Participants and examiner were masked to the axis and power of the astigmatism. Results All participants demonstrated similar variability in performance across acuity charts ( p = 0.54). For all charts, there was a linear reduction in VA with increasing amounts of induced astigmatism. The K eeler crowded Log MAR acuity test required the least amount of astigmatic blur to exceed a 0.2 Log MAR threshold (1.17 D, for 90° induced astigmatism), while the crowded and single K ay pictures required the largest magnitudes (2.09 and 2.85 D for 90° induced astigmatism respectively). The most variable acuities were recorded within and between participants with the S heridan G ardiner chart. Conclusions The present study demonstrated that none of the acuity charts under test are likely to detect uncorrected astigmatic refractive error unless the magnitude of astigmatism is large. Given the limitations of other paediatric acuity charts under test, it is important that practitioners use a crowded, Log MAR letter chart as soon as it is feasible.