Reanalysis of Refractive Growth Reanalysis of Refractive Growth in Pediatric Aphakia and in Pediatric Aphakia and

PseudophakiaPseudophakiaSusan Whitmer, MDSusan Whitmer, MD11

Aurora XuAurora Xu22

Scott McClatchey, MDScott McClatchey, MD1,3,41,3,4

1 Naval Medical Center San Diego1 Naval Medical Center San Diego2 Byram Hills High School, Armonk NY2 Byram Hills High School, Armonk NY

3 Uniformed Services University of the Health Sciences3 Uniformed Services University of the Health Sciences4 Loma Linda University4 Loma Linda University

The authors have no financial interest in the subject matter of this poster.The authors have no financial interest in the subject matter of this poster.

The views expressed in this article are those of the authors and do not necessarily reflect the official The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the United States policy or position of the Department of the Navy, Department of Defense, or the United States

Government.Government.

IntroductionIntroduction

The growth of an aphakic or pseudophakic eye The growth of an aphakic or pseudophakic eye results in myopic shift. The vertex distance of a results in myopic shift. The vertex distance of a spectacle lens causes the effective power to be spectacle lens causes the effective power to be higher at the cornea; this is greatest in babies higher at the cornea; this is greatest in babies less than 6 months of age.less than 6 months of age.

In utero

“Aphakic” refraction+100 D

BUT THIS CANNOT BE: 100 D at spectacle plane => -500 D vergence at cornea

Adult

“Aphakic” refraction+11 D

At birth

“Aphakic” refraction+21 D

Vertex distance artifact in RRGVertex distance artifact in RRG

PurposePurpose

The current model for logarithmic refractive The current model for logarithmic refractive growth (RRG2) is defined by the slope of the line growth (RRG2) is defined by the slope of the line of aphakic refraction of aphakic refraction at the spectacle plane at the spectacle plane vs. vs. adjusted age. adjusted age.

We developed a new model “RRG3”, to address We developed a new model “RRG3”, to address the optical artifact induced by the vertex the optical artifact induced by the vertex distance.distance.

MethodsMethodsWe reanalyzed eyes previously studied for RRGWe reanalyzed eyes previously studied for RRG1,21,2. Children 10 years old or younger, . Children 10 years old or younger, at the time of cataract surgery, were included. Each study eye had recorded follow-at the time of cataract surgery, were included. Each study eye had recorded follow-up refraction data of at least 3.6 yr and at least equal to the age at first refraction + up refraction data of at least 3.6 yr and at least equal to the age at first refraction + 0.6 yr. For bilateral cases, only data from the right eye was used.0.6 yr. For bilateral cases, only data from the right eye was used.

Based upon the vergence at the different surfaces in the eye, a new formula, “W”, Based upon the vergence at the different surfaces in the eye, a new formula, “W”, was developed to calculate the IOL power required for a given refraction, axial was developed to calculate the IOL power required for a given refraction, axial length and IOL A constant:length and IOL A constant:

IOL power = vergenceIOL power = vergenceback of IOLback of IOL – vergence – vergencefront of IOLfront of IOL

We assumed that the radius of curvature of the cornea, axial length and We assumed that the radius of curvature of the cornea, axial length and thickness of the cornea are all proportionate, with a limit to the anterior thickness of the cornea are all proportionate, with a limit to the anterior cornea radius of 8.9mm.cornea radius of 8.9mm.

MethodsMethods

Using Excel Visual Basic for Applications and iteration, we calculated Using Excel Visual Basic for Applications and iteration, we calculated the IOL power for emmetropia (aphakic refraction at the natural lens the IOL power for emmetropia (aphakic refraction at the natural lens plane), based upon the available data for the study eyes at each age.plane), based upon the available data for the study eyes at each age.

From the IOL power for emmetropia, RRG3 was calculated as follows:From the IOL power for emmetropia, RRG3 was calculated as follows:

where AdjAR is the adjusted aphakic refraction, calculated for each where AdjAR is the adjusted aphakic refraction, calculated for each individual eye at the natural lens plane, and AdjAge is the same individual eye at the natural lens plane, and AdjAge is the same adjusted age we used for RRG2 (i.e., age + 0.6 yr). The “1" and “2" adjusted age we used for RRG2 (i.e., age + 0.6 yr). The “1" and “2" refer to the initial and follow-up measurements, respectively.refer to the initial and follow-up measurements, respectively.

ResultsResults• 78 pseudophakic and 70 aphakic eyes were analyzed.78 pseudophakic and 70 aphakic eyes were analyzed.

Age at surgery (yrs)

< 6 months at surgery

Mean follow-up time (yrs) Vision

Pseudophakic 0.25-6.1 24% 7.950 ≥ 20/40

14 < 20/40 & > 20/12017 ≤ 20/120

Aphakic 0.25-9.0 31% 11.335 ≥ 20/40

7 < 20/40 & > 20/10024 ≤ 20/100

ResultsResults

Age at Surgery RRG3 (D)

Surgery at any age

RRG3 (D)

Pseudophakic< 6 months -11 ± 4

P = 0.12 -13 ± 6

P < 0.01≥ 6 months -14 ± 7

Aphakic< 6 months -15 ± 9

P = 0.60 -16 ± 10≥ 6 months -17 ± 10

ConclusionsConclusions

The data did not show a difference in RRG3 The data did not show a difference in RRG3 between eyes that had surgery at less than 6 between eyes that had surgery at less than 6 months of age and those that had surgery at months of age and those that had surgery at 6 months of age or after.6 months of age or after.

There was a significant difference in RRG3 for There was a significant difference in RRG3 for pseudophakic and aphakic eyes.pseudophakic and aphakic eyes.

DiscussionDiscussion

• The observation that RRG3 was not found to be The observation that RRG3 was not found to be different for the different age groups is different for the different age groups is consistent with the hypothesis that the consistent with the hypothesis that the observed difference in RRG was due to the observed difference in RRG was due to the vertex distance artifact.vertex distance artifact.

• The "W formula," from which RRG3 was The "W formula," from which RRG3 was calculated, needs further testing in infant calculated, needs further testing in infant aphakic and pseudophakic eyes to assess its aphakic and pseudophakic eyes to assess its accuracy.accuracy.

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