Abstract
Objectives
To assess the impact of corrected myopia on the caloric test. Correction of myopia with spectacles or contact lenses results in alteration of the size of the retinal image. Previous laboratory experiments have demonstrated that gross changes in the size of the retinal image can result in recalibration or suppression of the vestibulo-ocular reflex (VOR).
Methods
Case-control study. 17 evaluable healthy volunteers with myopia corrected either by spectacles or contact lenses (case group) compared to 17 volunteers with no refractive error (control group). Complete Electro-Nystagmography inclusive of bithermal caloric testing undertaken for cases and controls. Assessment of hypoactive caloric responses based on normative laboratory values.
Results
7 of 17 cases and 1 of 17 controls demonstrated hypoactive caloric responses. In the spectacle users group, 6 of 11 (55%) had hypoactive responses. Spectacle users were significantly more likely than emmetropic controls to have hypoactive caloric responses (p<0.01; relative risk 9.3 {95 % Confidence Interval 1.3 to 66.9}).
Conclusions
1) A significant proportion of myopes using spectacles have suppression of the vestibulo-ocular reflex as demonstrated by the caloric test. This has implications for the interpretation of ENG results, and also as a cause of vestibular impairment. 2) Further studies in myopes are warranted for precise and direct evaluation of the VOR by rotation or impulse testing.
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