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Abstract #3485 Published in IGR 4-2
Magnification characteristic of a +90-diopter double-aspheric fundus examination lens
Ansari Shahrezaei S; Stur MInvestigative Ophthalmology and Visual Science 2002; 43: 1817-1819
PURPOSE: To investigate the magnification characteristics of the +90-D double-aspheric fundus examination lens for biomicroscopic measurement of the optic disc. METHODS: A calibrated Gullstrand-type model eye adjusted for axial ametropia between -12.5 and +12.6 D was used to measure the change in magnification of the system with refractive error and variation in fundus lens position. A correction factor p (in degrees per millimeter) at different axial ametropias was also calculated. RESULTS: The total change in magnification of the system from myopia to hyperopia was -15.1% to +13.7%. When the fundus lens position was altered with respect to the model eye by ± 2 mm under myopic conditions, the change in magnification of the system was -4.8% to +8.1%. In the hyperopic condition the change was -4.8% to +6.0%. The fundus lens exhibited a linear relationship between p and the degree of ametropia of the model eye and a constant relationship between p and ametropia of -5 to +5 D. CONCLUSIONS: Axial ametropia has a significant effect on biomicroscopic measurement of the optic disc with the +90-D lens. Therefore, a correction factor (p) was calculated that can be used in calculations for determining true optic disc size. These findings may be important for improving clinical disc biometry.
Dr. S. Ansari Shahrezaei, Department of Ophthalmology and Optometry, University of Vienna Medical School, Vienna, Austria. siamak.ansari-shahrezaei@akh-wien.ac.at
Classification:
6.3.2 Posterior segment (Part of: 6 Clinical examination methods > 6.3 Biomicroscopy (slitlamp))
