Effects of Eye Registration on the Astigmatism Correction in the Surface Laser Ablation

PURPOSE: To compare the effect of astigmatism correction upon Mel 80 excimer laser surgery with or without an eye registration system. METHODS: This retrospective analysis investigates a group (eye registration group) of surface laser ablation surgeries for myopic astigmatism correction, with operation on 27 eyes from 15 patients with guidance of the eye registration system and 40 eyes from 29 patients without guidance from the eye registration system. The evaluation of astigmatism correction was performed by the Alpins method, measuring the amount and axis of astigmatism before and after the operations. RESULTS: The average of the correction index (the ratio of the surgically induced amount of astigmatism correction to the intended amount of astigmatism correction) for the eye registration group was calculated to be 0.94+/-0.30 and, for non-eye registration group, was 0.92+/-0.41, showing no statistical significant difference between the two groups (p=0.762). However, the comparison of the index of success (the ratio of the difference vector to the intended amount of astigmatism correction) favorably demonstrated the effectiveness of eye registration (0.23+/-0.34 for eye registration group, 0.47+/-0.54 for non-eye registration group, p=0.03). The absolute angle of error (AE), a measure of difference in angle between the ablated axis of astigmatism correction and the desired axis of astigmatism correction, was lower on average for the eye registration group than for the non-eye registration group (3.52+/-7.69 to 12.5+/-20.69 degrees, p=0.015). CONCLUSIONS: Eye registration-guided surface laser ablation is suggested to be beneficial for the reduction of errors in astigmatism correction.

Evaluation of Criteria of Stereoacuity for Titmus, Randot & TNO Stereotests

The commonly used tests for stereopsis are Titmus-fly, Randot, and TNO tests. In this study, 50 normal subjects were tested with these tests in order to set a criterion for normal stereopsis. The value of mean, mode and 75% point of these three tests were derived and compared.These three tests were also performed in 23 intermittent exotropes and 32 accommodative esotropes who showed gross stereopsis in the range of 60 to 400 seconds of arc by Titmus-fly testing. The aim was to obtain standards for clinical applicability and accuracy of these tests.This study cincludes that the appropriate criteria for normal stereopsis are less than 60 seconds of arc for Titmus-fly or Randot test, and 120 seconds of arc fot TNO test. Accurate testing for stereopsis in patients with gross stereopsis requires both Titmus-fly and Randot tests together. TNO test was inferior to the other two tests in terms of the accuracy and clinical applicability.