Refractive growth in pediatric aphakia and pseudophakia, and how to choose IOL powers for children Naval Medical Center, San Diego Uniformed University of the Health Sciences, Bethesda MD Loma Linda University, Loma Linda CA Scott K. McClatchey, MD Presenter has no financial interest in the products discussed The opinions expressed in this paper are solely those of the authors, and do not reflect the official policy or position of the Department of the Navy, the Department of the Defense, or the US Government.

Start with the goal in mind Good vision Emmetropia in adulthood Case history: NJM Posterior lenticonus cataract OD Cataract extraction & IOL at age 3.8 yr (1994) Initial postop refraction = +1.25 D What does his refractive future hold?

What does the data show? There can be large myopic shifts after cataract surgery, with or without IOL implantation Cataract surgery (age >6 months) does not affect the growth of the eye The refractive growth follows a logarithmic curve, with a characteristic Rate of Refractive Growth (RRG, now revised as RRG2) This knowledge can be used to predict future refractions

Aphakic refraction Declines with age: “myopic shift” From birth to 20 years: -10.0 D Patient with bilateral CE at 1 yr 281 aphakic eyes McClatchey & Parks, JPOS 1997

Myopic shift in aphakic eyes is due to the normal growth of the eye Natural lens power decreases from +34 to +19 D As the eye grows, aphakia and pseudophakia must result in a myopic shift “Gordon & Donzis data” are “aphakic refractions” in 148 eyes of normal children, calculated from measured AL and K. Archives of Ophthalmol 1985

Aphakic refractions follow a logarithmic curve Thus a plot of refraction vs. log of age is a straight line The slope of this line is defined as the Rate of Refractive Growth (RRG) Slope = RRG Semi-log plot of refraction vs. age (aphakic eyes) Slope = RRG McClatchey & Parks, JPOS 1997

RRG2 has dimensions of diopters Note: RRG2 accounts for the growth of the eye in utero, by adding 0.6 yr to each age measurement, to RRG2 = Refraction2 – Refraction1 Log(age2 +0.6 yr) – Log(age1 +0.6 yr) Log(age2 +0.6 yr) – Log(age1 +0.6 yr) = Log( [age2 +0.6 yr] / [age1 +0.6 yr] ) (a property of logarithms) Therefore, the unit of time drops out of the equation for RRG2

What does RRG2 mean? When a child’s age increases ten-fold, the aphakic refraction changes by RRG2 Example: If RRG2 = -6.4 D, then from age 0.4 to 10.4 yr (10 years): the aphakic refraction declines by 6.4 D

RRG2 is nearly the same in aphakic, pseudophakic and normal eyes Based on pooled long-term FU refraction data: Aphakic RRG2 = -6.8 D Pseudophakic RRG2 = -6.4 D Normal eyes RRG2 = -6.7 D (based on Gordon & Donzis data) (for eyes with surgery at > age 6 mo.) Small difference in RRG found McClatchey et al, Ophthalmology 2000

RRG2 allows prediction of pseudophakic refractions Future refractions are easily predicted for any pseudophakic eye and at any age The Pediatric IOL Calculator program McClatchey, JCRS 1998

RRG2 is useful in research RRG2 eliminates the confounding effects of: age at surgery length of follow-up initial refraction IOL power Because of the logarithmic refraction curve, FU times should be > age at surgery Slope is the same regardless of start age, end age, or FU time All other analytic methods are confounded by these factors Myopic shift varies with start and end age; thus you cannot directly compare data from two patients

RRG2 varies from eye to eye Standard Deviation = 45% of RRG2, after removing the effect of measurement error Some eyes grow faster than others We do not know why

IOLs increase myopic shift because of optics Analogous to the effect of vertex distance As the eye grows, the IOL gets farther from the retina May cause an increase in myopic shift of 1 to 6 diopters, depending on the patient and the IOL The greater the IOL power, the greater the myopic shift

RRG2 can be used for piggyback IOLs Hypothetical patient with piggyback IOLs implanted at 33 weeks gestational age

Choice of initial post-op refraction Start with the goal in mind Good visual acuity Emmetropia in adult life No data conclusively supports initial emmetropia vs. myopia vs. hyperopia My preference: moderate hyperopia based on age and refraction of the opposite eye

Considerations for initial post-op refraction Age of patient Amblyopia management Refraction of the other eye Ultimate refraction goal Variance in RRG2 Social & family issues Parents’ choice

Goal initial post-op refraction Surgery Refraction at age:* Age IOL Initial 1 yr 2 yr 20 yr 6 mo. 25 +6.5 +4.9 +3.0 -4.9 2 yr. 22 +4.0 -3.5 8 yr. 20 +1.0 -2.0 * Predicted refractions are shown in italics All predictions are based on “typical eyes” and are subject to the large variance in RRG2

Back to our case history: What does his refractive future hold?

Predicted refraction curve Actual refraction data (red squares)

In summary The optics of the growing eye can result in a large myopic shift after cataract surgery Cataract surgery (>6 months) does not affect the growth of the eye Refractive growth follows a logarithmic curve This knowledge can be used to easily predict future refractions

The future for these children Glasses or contact lenses PRK / LASIK Other refractive surgery