Model eyes for evaluation of intraocular lenses

Abstract

In accordance with the present international standard for intraocular lenses (IOLs), their imaging performance should be measured in a model eye having an aberration-free cornea. This was an acceptable setup when IOLs had all surfaces spherical and hence the measured result reflected the spherical aberration of the IOL. With newer IOLs designed to compensate for the spherical aberration of the cornea there is a need for a model eye with a physiological level of spherical aberration in the cornea. A literature review of recent studies indicated a fairly high amount of spherical aberration in human corneas. Two model eyes are proposed. One is a modification of the present ISO standard, replacing the current achromat doublet with an aspheric singlet cut in poly(methyl methacrylate) (PMMA). The other also has an aspheric singlet cut in PMMA, but the dimensions of it and the entire model eye are close to the physiological dimensions of the eye. They give equivalent results when the object is at infinity, but for finite object distances only the latter is correct. The two models are analyzed by calculation assuming IOLs with different degrees of asphericity to elucidate their sensitivity to variation and propose tolerances. Measured results in a variant of the modified ISO model eye are presented.

Energy efficiency of a new trifocal intraocular lens

“…We have also used commercial optical design software (Zemax Development Corporation, San Diego) to obtain the SA in two physiological eye models, namely the Liou-Brennan and the Holladay models. [31] The results, also plotted in Figure 4, show a good agreement with the experimental values, thus confirming that the modified-ISO model provides levels of SA similar to the values found in the aforementioned physiological eye models and measured in human corneas. [21,22] …”

Impact of corneal aberrations on through-focus image quality of presbyopia-correcting intraocular lenses using an adaptive optics bench system

“…10,11 The International Organization for Standardization (ISO 11979-2) recommends the use of a model eye with an aberration-free artificial cornea, 12 and this configuration is appropriate for the measurement of the isolated wavefront aberrations of an IOL. 10,11 However, Norrby et al 13 found that an aberration-free artificial cornea may not be the ideal configuration for a realistic reproduction of the pseudophakic retinal image quality in a model eye.…”

New trends in intraocular lens imaging

“…These aberrations are compensated in part by internal optics, particularly the crystalline lens, so that total values measured for the optical system of the eye are lower than for the cornea alone [12][13][14][15]. Regarding spherical aberration (SA), the average human cornea shows a prolate like shape that, in terms of the c [4,0] Zernike coefficient, produces a natural positive SA of about 0.3μm for a pupil diameter of 6mm [16]. These facts led to a new design for the IOL that, analogously to the young crystalline lens, introduced opposite aberrations to that of the cornea.…”

“…The current ISO standard is under revision [32]; for the next edition, an eye model with an artificial cornea that would reproduce the level of the SA of the average human cornea is being considered. Some modifications of the current ISO eye model as well as a practical realization called "physiological model eye," with dimensions close to the natural eye have been proposed and analysed in [33]. An aspheric lens used as an artificial cornea is expensive and difficult to manufacture.…”