This article is more than 5 years old. Information may no longer be current.
Cryotherapy does not change refractive error status in eyes with severe ROP
Instead, it prevents retinal detachment and allows refractive error assessment in some eyes.
Click Here to Manage Email Alerts
PHILADELPHIA — According to a recent study evaluating the effect of cryotherapy on refractive error status, cryotherapy does not change refractive error status in eyes with severe retinopathy of prematurity (ROP).
The study evaluated the effect of cryotherapy on refractive error status between ages 3 months and 10 years in children with birth weights of less than 1,251 g in whom severe ROP developed in one or both eyes during the neonatal period. Included in the study were 291 children born between January 1, 1986 and November 30, 1987.
“During the neonatal period, 240 of the infants developed bilateral severe (threshold) ROP, defined as a minimum of five contiguous or eight cumulative clock hours of stage 3+ ROP in zone 1 or zone 2. In these infants, one eye was randomly assigned to undergo cryotherapy and the other eye assigned to serve as a control,” said Graham E. Quinn, MD, from Children’s Hospital of Philadelphia.
The other 51 babies developed severe ROP in only one eye, and that eye was randomly assigned to receive cryotherapy or to serve as a control. Follow-up eye examinations, which included cycloplegic retinoscopy, were performed at 3 months and at 1, 2, 3.5, 4.5, 5.5, 7, 8, 9 and 10 years after randomization. Randomization coincided approximately with the child’s term due date.
At the 3-month examination, the cycloplegic agent used was 0.5% cyclopentolate. At the later follow-up examinations, 1% cyclopentolate was used. “When cyclopentolate was medically contraindicated in the opinion of the treating ophthalmologist, 1% tropicamide was used. Eye examinations were performed by ophthalmologists who had undergone a training and certification procedure that included quality control comparisons of retinoscopy results,” Dr. Quinn explained.
Refraction
A plus cylinder convention was used to record astigmatic errors. Additionally, examiners noted when refraction was not possible because of retinal detachment, media opacity or papillary miosis.
“At all ages, the proportion of eyes that could not be refracted is approximately twice as great in the control group as the treated group. Among eyes that could be refracted at 3 months, the distribution of refractive errors in treated eyes was similar to that for control eyes,” he said.
At all other follow-up examinations, the distribution of refractive errors from 8 D of myopia to high hyperopia in treated eyes was similar to control eyes. However, at all follow-up examinations except the one at 3 months, the proportion of eyes with 8 D or more of myopia was much higher in treated eyes than in control eyes. At all examinations, the proportion of eyes that were unable to be refracted because of retinal detachment, media opacity or papillary miosis was much higher in control eyes than in treated eyes.
Additionally, more treated eyes than control eyes had astigmatic errors of 1 D or more. But because there is a high correlation between refractive error of fellow eyes, these results may be confounded by the inclusion of two eyes from some patients and only one eye from other patients.
“Therefore, we examined the data from the subset of patients who had bilateral threshold ROP (one treated eye and one control eye) and in whom both eyes provided refractive error data. In this subset, the distributions of refractive errors in treated versus control eyes were similar at most ages,” Dr. Quinn said.
According to Dr. Quinn, the number of patients providing data at each age was substantially less than the total number of patients with bilateral threshold ROP because of the large number of eyes that had retinal detachment and could not be refracted.
Refractive error
The distribution of refractive error was similar in treated and control eyes at 3 months and 1 year. At later follow-up examinations, more treated eyes than control eyes had 8 D or more of myopia.
“Comparison of the treated and control refractive error distributions across the serial examinations was conducted using a linear mixed model, which takes into account the correlation of measurements made in the same patients at different ages. The mean differences in refractive errors between treated and control eyes were not significant,” Dr. Quinn said.
“In addition, we conducted an analysis to determine if there was a trend across age in differences in spherical equivalent refractive errors bet ween treated and control eyes. The result was not significant; that is, the slope of the differences over time was not significantly different from zero,” he added.
For Your Information:
- Graham E. Quinn, MD, can be reached at the Division of Pediatric Ophthalmology, The Children’s Hospital of Philadelphia, One Children’s Center, Philadelphia, PA 19104; (215) 590-2791; fax: (215) 590-4325; e-mail: quinn@email.chop.edu.
Reference:
Quinn GE, Dobson V, et al. Does cryotherapy affect refractive error? Ophthalmology. 2001;108:343-347.