engleski

SRK FORMULA IN EMMETROPS AND HYPEROPS

Purpose: Evaluation of SRK prediction of intraocular lenses (IOL) power in emmetropic and hyperopic cataractous eyes. Methods: 40 emmetropic (10 (25%) male and 30 (75%) female) and 40 hyperopic (24 (65%) male and 16 (35%) female) cataractous eyes of patients for extracapsular cataract extraction (ECCE) followed by posterior chamber lens implantation (PC IOL), were submitted to prospective evaluation of preoperative IOL power vs. postoperative refraction. Preoperative refractive state was defined according to calculated IOL power, using SRK formula, as follows:20 diopters (dpt) * emmetropic eyes * 22 dpt, hypermetropic eyes * 22 dpt. ECCE and PC IOL was done by the same surgeon performing the same operative technique, using the same intraocular lens: NB 57 polymethilmetacrylat "one piece" of A constant 118,5. Postoperative refraction spheral equivalent (SE) was evaluated (skiascopy, Bausch-Lomb keratometry (refractive index 1,3375), visual acuity Snellen chart testing) 2, 4 and 8 weeks following surgery and then in 2 months intervals until permanent refractive state was achieved. Results: Emmetropic group (mean implanted IOL power 21,33 dpt) divided, dependant upon IOL into two subgroups, had mean arithmetic value of spheral equivalent of permanent postoperative refraction (MA) 0.37 dpt with standard deviation (SD) 0,31 dpt. Surprisingly high MA, SD and especially standard error of estimate (SEE) differences between two emmetropic groups were found. Hyperopic group (mean implanted IOL power 23,3 dpt), with three subgroups, had MA 0.69 dpt. with SD 0.35 dpt. The highest MA (1,50 dpt), SD (0,50 dpt) and SEE (1,56 dpt), were found for extremely short eyes (IOL * 25 dpt) while SE, SD and SEE of first two hypermetropic groups, only slightly differed. SE follow-up in time intervals displays SE reducing rate, that is almost linear. The fourth postoperative week SD represents time-SE relation ascendant portion that abruptly declines, dependent upon postoperative astygmatism lessening. Final visual acuity (VA) for emmetrops ranged 0,7-1,0. The same percent as in hyperops (47,5) had 1,0 and the rest was divided as follows: 25% 0,7, 17,5% 0,8 and 10% 0,9.25% of hyperops had VA 0,8, 15% had 0,9 and 7,5 % 0,7. Only two patients had unsatisfactory visual outcome, 0,3 and 0,2. Preoperative SRK IOL prediction aimed to emmetropisation. Congruently, SE diminution produced linear postoperative VA accretion in emmetrops as well as hyperops. Both groups SE less than 0,5 dpt was found in 45% emmetrops and in 37,5% hyperop. The difference is more pronounced for SE up to 1,0 dpt being present in 90% emmetrops, but only in 67,5 % hyperops. In both groups 100% of patients had power prediction errors * 2,0 dpt. Conclusion: SRK formula gives excellent results in emmetrops, especially with IOL 20,00-21,00 dpt. It's prediction value decreases in hyperops, getting unsatisfactory in IOL * 25,00 dpt subgroup. In such cases, another, for example Holladay formula, should be used.

echobiometry; emmetrops; hyperops; SRK formula

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