A comparison of laser photocoagulation with cryotherapy for threshold retinopathy of prematurity at 10 years: part 2. Refractive outcome

Abstract

Objective To compare the refractive outcome of eyes treated with cryotherapy for threshold retinopathy of prematurity (ROP) with eyes treated with laser photocoagulation. Design Extended follow-up of a randomized controlled clinical trial. Participants One hundred eighteen eyes from 66 patients were randomly assigned to receive either cryotherapy or laser photocoagulation for threshold ROP. Twenty-five patients (44 eyes treated) were available for follow-up examination 10 years later. Intervention Cycloplegic autorefraction or retinoscopy was performed. Immersion ultrasound biometry (A-scan) was also performed, and an autokeratometer was used for keratometry. If an A-scan could not be tolerated or the patient was not cooperative, a B-scan through-the-lid biometry was performed. Corneal thickness was measured using optical coherence tomography. Main and secondary outcome measures Refractive error. In addition, anterior chamber depth, lens thickness, and axial length were measured. Central corneal thickness measurements and keratometric readings were also obtained. Result Eyes treated with cryotherapy were significantly more myopic than those treated with laser photocoagulation. When comparing patients with bilateral treatment, the mean spherical equivalent (SE) of eyes treated with laser was −4.48 diopters (D) compared with a mean SE of −7.65 D for eyes treated with cryotherapy (n = 15 pairs of eyes, P = 0.019). Cryotherapy-treated eyes had a mean axial length of 21.7 mm versus 22.9 mm for laser-treated eyes ( P = 0.024, n = 12 pairs of eyes). The anterior chamber depth and lens thickness averaged 2.86 mm and 4.33 mm, respectively, in the cryotherapy-treated eyes compared with 3.42 mm and 3.95 mm in the laser-treated eyes ( P < 0.001, n = 12 pairs for both measurements). There were no statistical differences in anterior corneal curvature and central corneal thickness between the two treatment modalities. Crystalline lens power bore the strongest correlation to refractive outcomes in both laser-treated ( r = 0.885, P < 0.001) and cryotherapy-treated eyes ( r = 0.591, P = 0.026). Although keratometric readings were higher than normal values in these eyes, there was no correlation to the degree of myopia. Conclusions Laser-treated eyes were significantly less myopic than cyrotherapy-treated eyes. Lens power seemed to be the predominant factor contributing to the excess myopia.