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(Investigative Ophthalmology and Visual Science. 2002;43:1817-1819.)
© 2002 by The Association for Research in Vision and Ophthalmology, Inc.

Magnification Characteristic of a +90-Diopter Double-Aspheric Fundus Examination Lens

Siamak Ansari-Shahrezaei and Michael Stur

From the Department of Ophthalmology and Optometry, University of Vienna Medical School, Vienna, Austria.

PURPOSE. To investigate the magnification characteristic 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.




eLetters:

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Magnification Errors with Fundus Lenses
John V. Arnold, et al.
IOVS Online, 4 Nov 2002 [Full text]
Author Response: Magnification Errors with Fundus Lenses
Siamak Ansari-Shahrezaei, et al.
IOVS Online, 4 Nov 2002 [Full text]

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Copyright © 2002 by the Association for Research in Vision and Ophthalmology