J Korean Ophthalmol Soc.  1988 Feb;29(1):83-92.

Effect of A Constant in SRK(TM) Formula on the Determination of Intraocular Lens Power

• Lee MK
• Lee Y
• Park BI

Abstract

There are a number of formulas to calculate the implant power in cataract surgery, but SRK(TM) regression formula has been used to calculate the power of over 90% of all IOLs implanted in U.S.A.. The same may be said of our country. A constant in the SRK(TM) formula exerts an influence on the accuracy of any implant power calculation by various factors. Furthermore, it is suspicious that A constant designated in West shall apply to the Koreans, because anatomical structure of the eye between the two is more or less different. Therefore, in order to achieve the desired postoperative refractive state, it is desirable to individualize the SRK(TM) regression formula by calculating a revised A constant using a given style of lens implant from the same manufacturer. This study included 418 posterior chamber lenses of 5 different styles undergoing cataract surgery with IOL implantion in the Department of Ophthalmology, Chonnam University Hospital. Revised A constants were calculated retrospectively by evaluating the results. Predicted postoperative refractive state after IOL implantation of the power given by using Binkhorst formula, SRK(TM) formula with designated A constant and SRK(TM) formula with revised A constant, respectively, and actual postoperative refractive state were compared and analyzed to evaluate the accuracy among those three groups. The results were as follows: 1. The revised A constants obtained from retrospective analysis were as follows: IOLAB, 116.1; 3M, 115.1; Cilco with angulated haptics, 116.4: Copeland, 116.1; Cilco with uniplanar haptics, 115.2. The revised A constants in all the styles of implants were more or less reduced than the designated A constants. 2. There were no difference in the revised A constants between phacoemulification group and planned extracapsular cataract extraction group. 3. In all the styles of IOLs, the SRK(TM) formulas with revised A constants weremore accurate than the Binkhorst formulas and the SRK(TM) formulas with designated A constants in deternining IOL power. 4. In accuracy according to variable axial lengths and corneal refractive powers among those three groups, better result was obtained in the SRK with revised A constant.

MeSH Terms

Cataract
Cataract Extraction
Jeollanam-do
Lenses, Intraocular*
Ophthalmology
Retrospective Studies