Pre-clinical estimation of the intraocular lens A-constant, and its
relationship to power, shape factor, and asphericity

Michael J. Simpson

doi:10.1364/AO.426155

Applied Optics
Vol. 60,
Issue 19,
pp. 5662-5668
(2021)
•https://doi.org/10.1364/AO.426155

Pre-clinical estimation of the intraocular lens A-constant, and its relationship to power, shape factor, and asphericity

Michael J. Simpson

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Michael J. Simpson, "Pre-clinical estimation of the intraocular lens A-constant, and its relationship to power, shape factor, and asphericity," Appl. Opt. 60, 5662-5668 (2021)

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Abstract

Calculating the intraocular lens power for a particular patient requires an empirical “lens constant” to estimate the final axial location after surgery. This is normally calculated from clinical results for each new lens style, but it can also be estimated without clinical data by comparing a new style to an existing style. The lenses are axially positioned in a model eye at comparable locations, and image distances are used to estimate the change in lens constant. The A-constant used by the SRK/T calculation method is evaluated here, but this can be easily converted for other calculations using an average eye. Raytrace calculations demonstrate the method, and also illustrate the effects that refractive index, shape factor, and asphericity have on the refractive error. Actual lens measurements at 35°C in saline are preferable if details of the reference lens are uncertain.

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Data Availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Design	Index	D	r1 mm	A4* 10^6	A6* 10^6	Ct mm	r2 mm
Equi sph	1.55	21	20.333	0	0	0.695	−20.333
Equi sph	1.55	23	18.558	0	0	0.738	−18.558
Cxp sph	1.55	21	10.294	0	0	0.701	−1000
Cxp sph	1.55	23	9.391	0	0	0.747	−1000
Pcx sph	1.55	21	1000	0	0	0.701	−10.294
Pcx sph	1.55	23	1000	0	0	0.747	−9.391
Equi asph SA0	1.55	21	20.334	−151.5	−0.8	0.682	−20.334
Equi asph SA0	1.55	23	18.559	−174.8	−1.1	0.723	−18.559
Cxp asph SA0	1.55	21	10.294	−43.0	−0.5	0.698	−1000
Cxp asph SA0	1.55	23	9.391	−50.6	−0.7	0.742	−1000
Pcx asph SA0	1.55	21	1000	−403.6	−1.7	0.667	−10.294
Pcx asph SA0	1.55	23	1000	−488.6	−2.6	0.705	−9.391
Equi asph SA0.3	1.55	21	20.336	−553.8	−6.0	0.646	−20.336
Equi asph SA0.3	1.55	23	18.561	−576.2	−6.5	0.687	−18.561
Cxp asph SA0.3	1.55	21	10.294	−431.5	−8.1	0.661	−1000
Cxp asph SA0.3	1.55	23	9.391	−436.3	−8.7	0.705	−1000
Pcx asph SA0.3	1.55	21	1000	−820.8	−4.5	0.632	−10.294
Pcx asph SA0.3	1.55	23	1000	−906.5	−5.3	0.669	−9.391
Equi sph	1.46	21	11.766	0	0	1.028	−11.766
Equi sph	1.46	23	10.736	0	0	1.105	−10.736
Cxp sph	1.46	21	5.940	0	0	1.068	−1000
Cxp sph	1.46	23	5.420	0	0	1.160	−1000
Pcx sph	1.46	21	1000	0	0	1.068	−5.940
Pcx sph	1.46	23	1000	0	0	1.160	−5.420
Equi asph SA0	1.46	21	11.767	−353.1	−5.0	0.996	−11.767
Equi asph SA0	1.46	23	10.737	−420.6	−6.9	1.066	−10.737
Cxp asph SA0	1.46	21	5.940	−214.8	−6.5	1.046	−1000
Cxp asph SA0	1.46	23	5.420	−295.3	−11.1	1.129	−1000
Pcx asph SA0	1.46	21	1000	−1300	−22.1	0.946	−5.940
Pcx asph SA0	1.46	23	1000	−1607	−33.8	1.006	−5.420
Equi asph SA0.3	1.46	21	11.770	−1038	−16.1	0.932	−11.770
Equi asph SA0.3	1.46	23	10.740	−1103	−18.6	1.002	−10.740
Cxp asph SA0.3	1.46	21	5.940	−853.5	−25.7	0.980	−1000
Cxp asph SA0.3	1.46	23	5.420	−925.3	−31.7	1.062	−1000
Pcx asph SA0.3	1.46	21	1000	−2037	−24.7	0.885	−5.940
Pcx asph SA0.3	1.46	23	1000	−2349	−35.7	0.944	−5.420

Abstract

Data Availability

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Applied Optics