Optical confirmation by a thick-lens formula of the optimized A-constant (as calculated by a thin-lens formula) of a
Giacomo Savini1, Daniela Nicolosi, Kenneth J Hoffer
1From the IRCCS Bietti Foundation, Rome, Italy (Savini, Schiano-Lomoriello); SIFI, Catania, Italy (Nicolosi, Curatolo); St. Mary's Eye Center, Santa Monica, California (Hoffer); Stein Eye Institute, Los Angeles, California (Hoffer); Studio Oculistico d'Azeglio, Bologna, Italy (Coutinho); Università di Bologna, Dipartimento di Farmacia e Biotecnologie, Bologna, Italy (Coutinho).
Purpose:
To provide a physical explanation for the A-constant of a new enhanced monofocal intraocular lens (IOL) by evaluating the relationship between the postoperative anterior chamber depth constant (ACD-constant) predicted by the Olsen formula, the ACD predicted by the Holladay formula, and the postoperative ACD measured by anterior segment optical coherence tomography (AS-OCT).
Setting:
IRCCS Bietti Foundation, Rome, Italy.
Design:
Retrospective case series.
Methods:
In a series of consecutive patients who underwent cataract surgery with the same enhanced monofocal IOL, the A-constant of the SRK/T formula was optimized. The postoperative distance between the corneal epithelium and the anterior surface of the IOL was measured by AS-OCT (MS-39) and compared with the ACD predicted by the Olsen formula (PhacoOptics) and the method described by Holladay to correlate the thin-lens IOL position with the thick-lens IOL position.
Results:
21 eyes were investigated. The back-calculated optimized A-constant was 118.33. The mean measured IOL distance from the corneal epithelium was 4.24 ± 0.28 mm. Based on the A-constant value of 118.33, PhacoOptics calculated that the mean predicted ACD constant specific for this IOL was 4.28 mm, while the mean predicted ACD based on the individual preoperative biometric parameters was 4.17 ± 0.23 mm. According to the Holladay method, the IOL distance from the corneal vertex was 4.21 ± 0.36 mm. Repeated measures analysis of variance disclosed that the difference among the 3 values was not significant ( P = .3535).
Conclusions:
The optimized A-constant correlates well with the thick-lens values calculated for the postoperative ACD.
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