EFFECT OF SPECTACLE CENTRATION ON STEREO ACUITY: A HOSPITAL-BASED STUDY AT MADINAH TEACHING HOSPITAL, FAISALABAD, PAKISTAN
Abstract
OBJECTIVES: To determine the fraction of decentered eyeglasses in this sample. To determine the possible effect on stereoacuity due decentration. To determine the difference between optical centration distance (OCD) and interpupillary distances (IPD). To determine the asthenopic symptoms due to decentration. To determine the prismatic effect`s magnitude. To determine the way of prism`s base in decentered glasses.
PATIENTS AND METHODS: A hospital based cross-sectional study conducted on the 100 students, with the age range of 18 to 26 years, of The University of Faisalabad in the Outpatient Ophthalmology Department at Madinah Teaching Hospital, Faisalabad. Horizontal decentration of glasses was measured by taking the difference between the interpupillary distance (IPD) and the optical center distance. Vertical decentration was evaluated by variance between the optical midpoint of the eyeglasses and the center of the pupils. Direction of decantation governs the direction of prism base and stereoacuity was judged by Titmus fly test.
RESULTS: 100% of the simple size were using decentered glasses in both horizontal and vertical direction. In both eyes horizontally decentration was maximum (33%) in the range of 0 – 1.49 (mm). The range of vertical decentration was 3 – 5 (mm) and highest, 39% in the right eye and 48% in the left eye of the individuals. Individuals having horizontal prismatic effect (PE) was56% in their glasses in both eyes within the range of 0 – 0.49Δ. Vertically prismatic effect was inside range of 0 – 0.99Δin all-out number of persons, 47% and 51% in the right eye and left eye respectively. Persons having induced base-in PE in their glasses was 76% in both eyes.17% have base-out prism in their right eyes and 18% in their left eyes. Vertically induced prism was in the base-up direction in 87% and 90% of the individuals in their right and left eyes respectively and 8% and 7% base-down prisms in their right and left eyes respectively. By applying paired T test the difference between IPD (interpupillary distance) and OCD (optical centration distance) of individuals was quite significant with p-value 0.000. The mean difference between IPD and OCD was -3.57000. Mean IPD was less than the mean OCD. Chi – square test result shows that the horizontal prismatic effect in right eye causes decline in the stereo-acuity with p-value 0.019. Highest number of individuals (42) have reduction of stereo-acuity within the range of 20 – 100 minutes of arc having horizontal prismatic effect in the range of 0 – 1.49 in their right eyes.
CONCLUSION: PE is induced due to the unfitting administration of glasses that shifts the position of image that formed on the retina resulting in the reduction of the stereo acuity of the individuals.