Possible errors in the measurement of retinal lesions

Abstract

Purpose: To determine the accuracy of the measurement of structure in the retina from fundus photographs.

Method: A model eye was developed to measure the retinal image size of the Zeiss fundus camera. A x 10 microscope objective with a focal length of 16.41 mm was used together with a microscope graticule.

Results: Under emmetropic conditions the difference between the calculated and the measured magnification was 8.6%. The total change in magnification from myopia to hyperopia was -24.63% to +18.1%. When the camera position was altered with respect to the model eye by +/- 5 mm under myopic conditions the change in magnification was -4.5% and +6.8%. In the hyperopic condition the change was -5.6% to +4.6%.

Conclusions: Measuring the size of structure in the retina from photographs may therefore prove to be inaccurate but in some circumstances determining the percentage change in size may prove more reliable.