Abstract
Purpose: :
Light scatter in intraocular lenses may be a significant factor in quality of vision for patients implanted with these lenses. The purpose of this study was to develop two complementary quantitative methods for measuring light scatter in intraocular lenses. The measured amount of light scatter found in healthy crystalline lenses can be used as a basis for comparison.
Methods: :
Using Method 1, light was projected onto the intraocular lens (IOL) to determine the angular dependent light scatter. The IOL models were measured in a liquid cell. The IOL was first illuminated fully and then with a very narrow slit. Under slit illumination the scattered light was measured so that the bulk and surface scatter could be separated for large angles.Method 2 measures the light intensity distribution of an IOL in an eye model representing average chromatic and spherical aberration. The average cornea eye (ACE) model consists of a liquid cell and a cornea with spherical and chromatic aberration similar to the average human eye. Various wavelengths and pupil sizes were used while measuring the light intensity distribution of the IOL models.
Results: :
With Method 1 the light scatter was measured in several directions for both full and slit illuminations for angles larger than 3 degrees. Light scatter originated from the surface and/or the bulk of the lens, for example in the presence of micro vacuoles. Depending on the number and size of the micro-vacuoles, models of such lenses showed significant light scatter levels compared to a healthy crystalline lens.For Method 2, intensity profiles were stitched together to obtain a dynamic range of 6 log units and an angular field of approximately 3 degrees. Measurements of multifocal and monofocal IOLs with different pupil sizes enabled us to compare the pupil area ratio with the corresponding light power ratio. The measured multifocal lenses showed unequal ratios, indicating that all incoming light will not focus to the central field.
Conclusions: :
The two methods for measuring light scatter are complementary in the angular domain. The data they provide can form a basis for comparison with data from a healthy crystalline lens. It can be concluded that both methods are valuable for further improving quality and performance when designing IOLs.
Keywords: intraocular lens • imaging/image analysis: non-clinical • optical properties