Fundus measurements with indirect ophthalmoscopy. An experimental approach
C. G. Wells, J. L. Barrall and D. C. Martin
Department of Ophthalmology, University of Washington School of Medicine, Seattle.
We examined the factors influencing the accuracy of indirect
ophthalmoscopic estimates of choroidal tumor size by studying indirect
ophthalmoscope photographs of solid black domes implanted in the
suprachoroidal space of postmortem human eyes. Measurements of the indirect
ophthalmoscope photographs showed clinically significant differences in the
absolute diameter of the visualized fundus, which varied with differences
in condensing lens power and width, anteroposterior location of viewed
fundus, and axial length of the experimental eye. Linear regression
analysis demonstrated that the field of view of each condensing lens varied
similarly with axial length and that the majority of variation in field
size for each condensing lens was attributable to axial length variation.
Equatorial fields of view averaged 11% smaller than posterior fields of
view. The accuracy of estimated absolute intraocular dimensions using
indirect ophthalmoscopy potentially approaches +/- 5%.
