Vol.1 , No. 1, Publication Date: Jul. 7, 2014, Page: 7-10
[1] | Varuna Kumaran , Optometry Department, Sri Jayendra Institute of Medical Sciences and Research, Pammal, Chennai, Tamil Nadu, India. |
[2] | Prabeen Raj Mudvari , Optometry Department, Sri Jayendra Institute of Medical Sciences and Research, Pammal, Chennai, Tamil Nadu, India. |
[3] | Rupak Dhital , Optometry Department, Sri Jayendra Institute of Medical Sciences and Research, Pammal, Chennai, Tamil Nadu, India. |
(i) Purpose: To assess changes in visual acuity (VA) as a function of induced defocus by plus lenses till 5 D, in the Indian population using a computerized automatic measurement of VA. (ii) Methods: The study was done on 15 student volunteers. A complete optometric evaluation was done. Refractive errors did not exceed +/-1.00 DS, ± 0.50 DC, and were correctable to 6/6, N6. Subjects had no history of ocular diseases, binocular vision anomalies, and systemic diseases and were not on medications affecting pupil sizes or accommodation. With best correction, distance VA was tested and recorded automatically using LCD projected Freiburg Visual Acuity Test chart (FrACT3.8.0e software) placed at 6m, with Tumbling ‘E’. Plus lenses were added in front of the right eye alone, in steps of -0.50 DS, starting from -0.50 DS to -5.00 DS. An informal consent was obtained.The VA readings were automatically generated. The data was analyzed using the Statview Statistical Software (SAS Institute Inc.) by Repeated Measures ANOVA. (iii) Results: VA decreases with plus lens-induced defocus in 0.5 D steps till -5 D, overall (p-value <0.0001). Although there is a steady linear decrease in acuity upto -2 DS, beyond this the rate of decrease in acuity slows down and plateaus. (iv) Conclusion: With increase in myopic defocus, induced by plus lenses, VA reduces, albeit, non-linearly especially for higher amounts of defocus. Spectacle magnification as an artefact needs to be verified.
Keywords
Visual Acuity, Myopic Defocus, Emmetropes, Logmar, Decimal Acuity, Peripheral Defocus
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