In order to estimate the value of f0, the image size of an
object of known size and distance was obtained (Fig. 2).
The value of f0 was calculated by substituting the object
size (A), image size (B) and distance of the object from
the lens (s) into Eqs. (1)–(3). Values for f0 obtained in 55
specimens varied from 299 to 370 lm (334 ± 15 lm,
mean ± sd). The refractive index of the lens material (n1)
could be estimated based upon morphological parameters
and f0. In all 55 specimens the morphological parameters
t, re and ri, were measured in wholemount preparations
under a microscope after measurements of the magnifying
power of each lens. The specimens were divided into two
groups, which were examined by two different observers
(A and B in Table 2). Based upon these parameters,
1.90 ± 0.02 and 1.80 ± 0.05 were the values obtained for
apparent refractive index n1 by each respective observer.