Abstract
Purpose :
After an intraocular lens (IOL) implantation some patients report highly visible reflections similar to the reflexes seen in cat's eyes. In the published literature, flatter anterior IOL surfaces and high index materials are thought to be the cause. The purpose of the current study is to develop a theoretical model and a pre-clinical measurement setup enabling quantitative and qualitative assessment of such IOL reflections. This information can be incorporated at the IOL design stage to predict reflections and used to understand why some patients experience this phenomenon.
Methods :
For the theoretical evaluation a physiological eye model with an anatomically average cornea was implemented in Zemax. Reflection strength was quantified as peak intensity for an observer 1 m away from the patient. The radii of curvature giving high reflection intensities were thus determined. The sensitivity of the model to corneal radius, anterior chamber depth, wavelength and observer distance was assessed. Experimentally, several IOL models were evaluated in a physical eye model. The whole eye was illuminated with a light source and the reflection intensity was recorded. The IOLs evaluated were a standard aspheric lens (ZCB00 20 D, r=12 mm), a lens specially made to have a large reflection according to the model (r=26 mm), and a lens with an even flatter anterior surface design (r=1000 mm).
Results :
As it can be observed in Fig. 1, the reflection intensity as a function of radius of curvature can vary by several orders of magnitude. The reflection intensity is within the same order of magnitude over a wide range of corneal radii, wavelengths, anterior chamber depths and observer distances. The theoretical predictions were verified by the experimental data. For a 26 mm radius of curvature IOL, the strong reflection appeared as predicted (see Fig. 2).
Conclusions :
A model to predict anterior IOL reflections was developed and validated. Contrary to what has previously been assumed, flatter surfaces do not necessarily result in a stronger reflection. There is rather a critical range of anterior radii of curvature for which reflections are large. This is of particular importance for IOLs made with high index of refraction material, e.g. 1.55, where a biconvex design would give the highest reflectivity for a power of 17 D.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.