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Siamak Ansari–Shahrezaei, Noemi Maar, Robert Biowski, Michael Stur; Biomicroscopic Measurement of the Optic Disc with a High-Power Positive Lens. Invest. Ophthalmol. Vis. Sci. 2001;42(1):153-157.
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purpose. To compare the magnification properties of four different indirect
double aspheric fundus examination lenses for clinical disc biometry.
methods. Experimental study in a model eye. The relationship between the true
size of a fundus object and its image was calculated for each fundus
lens for an ametropic range between −12.5 and +12.6 D using a slit
lamp biomicroscope with adjustable beam length.
results. Equations for determining the correction factor p (degrees per millimeter) were calculated for each fundus lens. The
factor can be used in calculations to determine true optic disc size.
The total change in magnification of the system from myopia to
hyperopia was −21.1% to +24.0% (60-D lens; Volk Opticals, Mentor,
OH), −12.9% to +16.2% (Volk super 66 stereo fundus lens), −13.2%
to +13.9% (Volk 78-D lens), and −13.3% to +14.0% (Volk super-field
NC lens). When the fundus lens position was altered im relation to the
model eye by ±2 mm under myopic conditions, the change in
magnification of the system was −4.3% to +5.7% (60-D lens), −4.6%
to +6.1% (66 stereo fundus lens), −4.9% to +6.3% (78-D lens), and−
5.9% to +7.8% (super-field NC lens). In the hyperopic condition the
change was −2.7% to +3.6%, −3.4% to +4.5%, −3.6% to +4.8%, and−
4.5% to +6.0%.
conclusions. The study has shown that the use of a single magnification correction
value for each fundus lens may not be appropriate. These findings have
important implications for the way in which calculations for
determining the true optic disc size and other structures of the
posterior pole are performed using indirect
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