1. 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.

2. 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 = D What does his refractive future hold?

3. 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

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

5. 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

6. 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

7. 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 – Refraction Log(age yr) – Log(age yr)
Log(age yr) – Log(age yr) = Log( [age yr] / [age yr] ) (a property of logarithms)
Therefore, the unit of time drops out of the equation for RRG2

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

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

15. 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

16. 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

17. 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

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

19. Predicted refraction curve Actual refraction data (red squares)

20. 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

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