Myopia and astigmatism in retinopathy of prematurity after treatment with cryotherapy or laser photocoagulation

Background: Visual outcome studies have shown that laser photocoagulation may result in more favourable clinical outcomes than cryotherapy in threshold retinopathy of prematurity (ROP). Comparative refractive outcome studies have shown that patients treated with laser photocoagulation have less myopia than those treated with cryotherapy. We carried out a study to determine whether a difference in visual outcome or refraction exists in patients with threshold ROP who have been treated with cryotherapy vs. laser photocoagulation. Methods: A retrospective cohort study was conducted comparing treatment results after at least 3 years of follow-up in patients with threshold ROP treated with cryotherapy or laser photocoagulation at a tertiary care children's hospital. Visual acuity and refraction were the outcomes studied. Covariates measured were sex, gestational age and birth weight. Analysis was performed with both bivariate analysis and multivariate models. Results: Seventy-one eyes of 37 patients with threshold ROP were included in the study. Thirty-seven eyes received cryotherapy, and 34 eyes received laser photocoagulation. The mean spherical equivalent refraction was significantly lower in the cryotherapy group than in the laser photocoagulation group (-9.21 dioptres vs. -1.80 dioptres, p = 0.001). Patients in the cryotherapy group were more likely than those in the laser photocoagulation group to have against-the-rule astigmatism (odds ratio 6.86, p = 0.004). Laser photocoagulation did not significantly lower the frequency of an unfavourable visual outcome (visual acuity worse than 20/200) (p = 0.09). Interpretation: Eyes with threshold ROP treated with laser photocoagulation were significantly less myopic and less likely to have against-the-rule astigmatism than those treated with cryotherapy.