ISSN: 2375-3811
International Journal of Biological Sciences and Applications  
Manuscript Information
 
 
Changes in Visual Acuity as a Function of Defocus Induced by Positive Lenses
International Journal of Biological Sciences and Applications
Vol.1 , No. 1, Publication Date: Jul. 7, 2014, Page: 7-10
2060 Views Since July 7, 2014, 636 Downloads Since Apr. 14, 2015
 
 
Authors
 
[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.

 
Abstract
 

(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


Reference
 
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