Abstract
Purpose :
To study the changes in visual symptoms and halos for varying levels of spherical refraction error for different intraocular lens (IOL) technologies using optical bench testing.
Methods :
Seven IOL models (20D) with different characteristics were evaluated: 3 monofocal lenses with different levels of spherical aberration (SA), 1 enhanced aspheric monofocal that slightly extends depth of focus, 3 Extended Depth of Focus (EDF) lenses (1 diffractive, 2 refractive) and 1 multifocal.
The IOLs are tested using an optical bench and an eye model with a positive SA cornea. The object vergence is varied from ±1D in 0.5D steps. Images are taken in white light and a field of view of ±1 degree to produce a High Dynamic Range image where a halo size can be measured. Pupils of 5 and 4 mm are used.
Results :
Qualitatively, the images show that lenses designed to compensate corneal SA have a more symmetric halo behavior around 0D of defocus. Lenses with no or lower SA correction show much poorer performance towards the positive (hyperopic) side. The diffractive lenses, although designed to compensate corneal SA, also appear worse on the positive side.
At 5mm, the multifocal produces the largest halo radius with sizes 0.5 to 0.7 degrees. The spherical lenses produce larger than expected halo sizes with sizes 0.1 and 0.45 degrees especially with positive defocus. In some situations, this is larger than the EDF diffractive halo size (0.2 to 0.4 degrees). The monofocal, enhanced monofocal and the refractive EDF designed to compensate corneal SA show small halos and an almost symmetric performance around 0D (0.1-0.25 degrees). The remaining refractive EDF has larger halos towards the positive defocus (0.1-0.3 degrees).
Conclusions :
The results show that SA correction can play a large role in the size of visual halo disturbances in the presence of defocus. IOLs without corneal SA correction can, under some circumstances, produce halos comparable to those produced by some diffractive designs. For the lenses studied here, the behavior is worse towards the positive defocus side. Diffractive lenses also show some asymmetric behavior with respect to defocus while the monofocal, enhanced monofocal and refractive EDF with the highest correction of the SA IOLs show a very comparable and symmetric behavior around 0D. Future studies should consider the impact of other factors such scatter or starburst in the overall dysphotopsia profile.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.