Abstract
Purpose :
Optical quality measurements of intraocular lenses can be performed in the laboratory using the optical setup described in the ISO or ANSI standards for intraocular lenses. This optical setup includes a lens functioning as the cornea, and a water bath in which the IOL is placed. The optical power of the ISO standard cornea is described through the vergence and spherical aberration at the IOL plane. This study correlates the vergence with that of real corneas.
Methods :
Corneal strength data was collected through literature review. Since corneal power may differ by race or region, the obtained corneal power data was subdivided into geographical regions. The global average corneal power was obtained by the weighted averaged of all data.
Translation of the real world data to the standardized model eye was performed using the relative IOL position in the eye and the corresponding F-number. The corneal power of the standard eye model is defined by means of the vergence at the IOL plane: “the IOL front surface is placed at an axial location that is between 26 mm and 28 mm in front of the focal point of the model cornea itself.” For this standard eye using the average axial location of 27mm with a physical pupil diameter of 5.15 mm, this corresponds with an f-number of 3.92, which will be compared with the f-number of the weighted global average of real human corneas.
Results :
Data of corneal power (K) was obtained from sixteen (16) publications. Three studies were performed on a general population, and for these studies, where possible only the older age group was considered (≥60Y). The other 13 studies measured corneas of a cataract population. Geographical regions are represented by five (5) continents: Asia (n=3926, K=44.217D), Africa (n=765; K=44.350D), Europe (n=55639; K=43.668D), (North) America (n=7500; K=43.810D) and Oceania (n=176, K=43.718D). The data suggest that there are significant differences in corneal power between continents. The weighed global average corneal power was 44.15 Diopters, which corresponds with an f-number of 3.775. In the standard model eye this corresponds with a distance between the physical pupil (5.15 mm; IOL front surface) and focal plane of 25.97 mm.
Conclusions :
The global average human corneal power is 44.15 diopters. For the ISO standard eye, this means that the IOL front surface should be placed at an axial location that is 25.97 mm in front of the focal point of the model cornea.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.