The Effect of Unilateral Induced Astigmatism on Stereopsis

Document Type : Research Paper

Authors

1 Associate professor of Mashhad University of Medical Sciences

2 MSc in Optometry

3 Epidemiolojist, Assistant professor of Mashhad University of Medical Sciences.

Abstract

Introduction
 
Blur vision due to astigmatism and spherical refractive errors reduce stereopsis and develop amblyopia in children. The aim of this study was to determine the effect of different type and amount of induced unilateral myopic and hypropic astigmatic anisometropia on stereopsis.
 
Materials and Methods
 
This interventional study was performed on 60 normal patients after primary examination and refraction, the primary stereopsis was determined by TNO and Titmus stereotests. Myopic and hypropic astigmatic anisometropia were induced using trial lenses of 1 to 4 D, minus and plus in horizontal, vertical and oblique axis. The stereopsis was then determined by TNO and Titmus stereotests. Data were analyzed, using SPSS version 11.50.Patients with previous amblyopia, manifest deviations, ocular pathology and more than 4 prism heterophoria and abnormal fusion response with Bagolini test were excluded from the study.
 
Results
 
Mean stereopsis was 40.83±2.78 and 31.50±6.59 seconds of arc with Titmus and TNO stereotests respectivley before intervention in all patients. Stereopsis levels were reduced significantly with respect to the degree and types of meridional anisometropia (p< 0.001). Maximum reduction of stereopsis occurred with 4 D myopic and hypropic astigmatic anisometropia in oblique axis. It was 1930±271/5 and 1780±518/6 second of arc for TNO test and 773.33±101/4 and 693.33±/179.9 second of arc for Titmus stereotest. Comparison between mean stereopsis in myopic or hypropic astigmatic anisometropia was statistically significant in all three axes; horizontal, vertical and oblique (p< 0.000).
 
Conclusion
 
According to the findings of this study, uncorrected meridional anisometropia(myopic and hypropic anisometropia) like spherical anisometropia has advers effect on binocular vision development and stereopsis. It can also develop amblyopia in critical age of children. 4 D meridional anisometropia reduced stereopsis to below 1% which indicated liner relation between them. These findings show that the low oblique and vertical astigmatic anisometropia reduce stereopsis more than the horizontal axis.

Keywords

References

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Medical Journal of Mashhad university of Medical Sciences
Volume 53, Issue 2 - Serial Number 2
May and June 2009
Pages 90-97

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