The SRK II formula is based on the SRK I formula:
| SRK I: | P = A - 0.9 K - 2.5 L | (1) |
where:
| P | : | IOL power for emmetropia |
| K | : | corneal refractive power (K-reading) |
| L | : | axial length |
| A | : | A-constant |
| SRK II: | P = A1 - 0.9 K - 2.5 L | (2) |
The difference between SRK I and SRK II is given by the A1 constant. A1 is related to the A-constant A according to
| A1 = A + 3 | for | L < | 20 | |||
| A1 = A + 2 | for | 20 | < = | L < | 21 | |
| A1 = A + 1 | for | 21 | < = | L < | 22 | |
| A1 = A | for | 22 | < = | L < | 24.5 | |
| A1 = A - 0.5 | for | 24.5 | < = | L |
| I = P - cr R | (3) |
P is again given by SRK II (2), and cr is another empirical constant defined as
| cr = 1 | für | P | < = | 14 |
| cr = 1.25 | für | P | > | 14 |
HAIGIS W: Biometrie, in: Augenärztliche Untersuchungsmethoden, Straub W, Kroll P, Küchle HJ (Hrsg), F.Enke Verlag Stuttgart, 255-304, 1995
RETZLAFF J: A new intraocular lens calculation formula, Am Intra-Ocular Implant Soc J 6:148-152, 1980
RETZLAFF J, SANDERS DR, KRAFF MC: Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refract Surg 16 (3):333-340, 1990
RETZLAFF J, SANDERS DR, KRAFF MC: Lens Implant Power Calculation - A manual for ophthalmologists & biometrists, 3rd edition, Slack Inc, Thorofare NJ, USA, 1990
SANDERS DR, KRAFF MC: Improvement of intraocular lens power calculation using empirical data, Am Intra-Ocular Implant Soc J 6: 263-267, 1980
SANDERS DR, RETZLAFF J, KRAFF MC: Comparison of the SRK II formula and other second generation formulas. J Cataract Refract Surg 14: 136-141, 1988
(C) W.Haigis. Last revision: Feb.12, 1998