Commentary: Functional outcome after successful laser for retinopathy of prematurity - Where we stand?

Despite advances in screening and management, retinopathy of prematurity (ROP) is the leading cause of vision impairment in children worldwide. Ablation of peripheral avascular retina reduces the morbidity resulting from ROP and improves the structural outcome, but associated refractive errors, predominantly myopia, amblyopia, and strabismus limit the functional outcomes.[1]

High incidence of myopia in preterm infants has been reported in numerous studies, prevalence ranging from 0% to 16%. Association of ROP with myopia is also well known. ETROP study reported a myopia prevalence of 58% in infants with severe ROP, and higher (around 70%) in eyes who received laser photocoagulation.[1] Wang et al. concluded that infants receiving laser for severe ROP have early and rapidly progressive myopia compared with preterm infants with no/mild ROP. Various postulated mechanism of myopia following laser photocoagulation include arrested anterior segment growth or disturbed retinal signalling affecting normal ocular growth.[2] Most common reported parameters include increased lens thickness, steep corneal curvature, and shallow anterior chamber depth and higher axial length.

Geloneck et al. described higher myopia in eyes receiving laser as compared with those receiving bevacizumab, especially for zone 1 ROP. Similar findings were reported by various other studies as well.[3] On the contrary, Hwang et al. reported comparable refractive outcome in eyes with zone 1 disease following both bevacizumab and laser and stated that zone 1 disease is an independent risk factor for development of myopia.[4]

Long-term optical status and functional outcome following laser for ROP have been studied by various authors. Reported mean spherical equivalent ranges from around -2 to -6. Magnitude and occurrence of myopia as found by Shah et al. for zone 1 APROP was higher than other studies.[5]

Myopia observed by Anilkumar et al. was found to be associated with higher axial length, but unlike other studies, there was no association with lenticular thickness.[6] Kaur et al. found higher myopia was associated with higher lenticular thickness and axial length at 1-year postnatal age.[7] Various studies have discussed factors associated with occurrence of myopia in eyes with history of laser for ROP, the exact mechanism of its development is still controversial.[567] This may be because most of these studies are retrospective, cross-sectional studies, and lack of documentation of progression of myopia and serial measurement of biometric parameters. Moreover, it is difficult to ascertain whether the resultant myopia is due to severe ROP or laser.

High prevalence of astigmatism, mostly with the rule, has been a common observation after laser for ROP. Wang et al. reported a higher prevalence of astigmatism in lasered eyes with severe ROP than those with mild/no ROP.[2]

Around one-third of the children develop strabismus as reported by a study in this issue, possibly due to amblyopia and associated refractive errors.[6] Prematurity is a known independent risk factor for development of strabismus and these children require regular follow-up during their early years.

Sensory outcomes following treatment for ROP are scarcely reported in literature. Most of the studies report satisfactory long visual outcomes. Despite this, fine stereopsis was seen in only 15.6% patients by Anilkumar et al.[6] Similar results of lack of stereopsis were concluded by Bonotto et al.[8] It emphasizes the need for regular assessment and early identification of associated refractive error, amblyopia, and strabismus and a prompt intervention.

Screening programmes have brought awareness about ROP and has led to early treatment of these babies but further stress on periodic follow-up may help in improving the structural and functional outcome. Severe ROP is known to be associated with a myopic shift, but the role of laser photocoagulation and its contribution to myopia is still controversial. A long term, prospective- control study would help in understanding the mechanism of myopia development and progression in these eyes.