25c computers

refractive error for intraocular lens of known power program for hewlett packard 25/25c computers

PROGRAM FOR HP25 and 25/C RCL-6 RCL-1 X STO-7 RCL-2

X

Robert C. Drews i M.D. Clayton, Missouri

RCL-1 RCL-2

A very useful formula for the prediction of the refractive error generated by a given lens implant has been published by Richard Binkhorst 1 together with programs for the Texas Instrument SR-52 and Hewlett Packard 65 programmable computers. The much less expensive Hewlett Packard 25 and 25C computers are also capable of solving this equation using the simplified program given below.

X

R =. 1336(4r-a) - D(a-d)(4r-d) s 1336[ v(4r-a) + 0.003ar 1 - D(a-d)[ v(4r-d) + 0.003dr 1 where D = the dioptric power in aqueous of the intraocular lens r = the radius of curvature of the anterior surface of the cornea in mm a = the axial length in mm d = the distance between the anterior vertex of the cornea and the intraocular lens in mm v = the vertex distance in meters to the patient's spectacle Rs = the spectacle refraction in diopters

Note that by inserting D = 0, the patient's aphakic correction can be computed. This is useful in checking the accuracy of ultrasound equipment on patients who have already had cataract surgery, where this refractive error is known, and in predicting the aphakic refractive error in high myopes where there is a question about using intraocular lenses at all.

RCL-5

+

RCL-O X RCL-7 RCL-4 X RCL-1 RCL-4 RCL-5

X

+

RCL-2 RCL-4 RCL-3

X X

STO 7 RCL-1 RCL-4 RCL-4 RCL-2

X RCL-3 X RCL-1 RCL-2 RCL-O

To begin operation the following information must be stored into the computer: STO-O STO-1 STO-2 STO-3 STO-4 STO-5 STO-6

X

+

RCL-7

1336 4r = nc/K

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

24 24 23 24 24 24 24

24 24 24 24 24 24

24 24 24

23 24 24 24 24

24 24 24 24

24

06 01 61 07 02 61 01 02 41 05 61 51 00 61 07 04 61 01 04 41 05 61 51 02 04 41 03 61 61 41 07 01 04 41 04 02 41 61 03 61 01 02 41 00 61 51 07 71

.003/4 4r .003r (.003r)

a .003 ar 4r

a 4r-a v v(4r-a) [v(4r-a) + .003ar 1 1336 1336[v(4r-a) + .003arl .003r d .003dr 4r

d (4r-d) v v(4r-d) [v(4r-d) + .003dr 1

a d (a-d) D D(a-d) D(a-d)[v(4r-d) + .003drl Denominator Denominator 4r d (4r-d) d

a -(a-d) -(a-d)(4r-d) D -D(a-d) (4r-d) 4r

a 1336 1336(4r-a) Numerator Denominator Rs

a D

Reference:

d v (in meters) .003/4 = .00075

1. Binkhorst, R. D.: Pitfalls in the Determination of Intraocular Lens Power Without Ultrasound. Ophthalmic Surgery 7(3) 69-82, 1976.

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