Characteristics and associated factors of early refractive parameters in premature infants

Objective: To investigate the characteristics and associated factors of early refractive parameters in premature infants. Methods: Case-control study. Premature infants who underwent the first fundus screening in the ophthalmic clinic of Xiamen children's Hospital from May 2018 to February 2019 were collected. The screening time was 4 to 6 weeks after birth or corrected gestational age from 31 to 32 weeks. The premature infants who were diagnosed with mild retinopathy of prematurity (ROP) in one eye or both eyes but did not receive any treatment were divided into ROP group and divided into zone Ⅱ subgroup and zone Ⅲ subgroup according to the region of ROP; the premature infants without ROP were divided into non-ROP group. The gestational age, birth weight, spherical equivalent, anterior chamber depth, vitreous depth, axial length, lens thickness and corneal refractive power were recorded and compared. Independent sample t-test, multiple linear regression analysis and Pearson correlation analysis were used. Results: A total of 180 premature infants, 101 males and 79 females, with gestational age of (30.82±3.10) weeks, corrected gestational age of (37.21±1.44) weeks and birth weight of (1 577.85±572.12) g were included in this study. Ninety premature infants were included in the ROP group (162 eyes, of which 85 right eyes were included in the analysis) and 90 in the non-ROP group (90 right eyes). There was no significant difference in the distribution of gestational age, birth weight and corrected gestational age between the ROP group and non-ROP group (all P>0.05), but there was significant difference in the spherical equivalent between the two groups [(1.90±1.39) D vs. (3.04±1.88) D, t=-4.653, P<0.01], and ROP group was relatively smaller. In the ROP group, the anterior chamber depth was (1.82±0.23) mm, the lens thickness was (4.54±0.18) mm, and the corneal refractive power was (43.99±0.99) D. In the non-ROP group, the anterior chamber depth was (1.91±0.94) mm, the lens thickness was (4.23±0.50) mm, and the corneal refractive power was (43.72±0.92) D. The difference between the two groups was statistically significant (all P<0.01). In ROP group, the anterior chamber depth was shallower, the lens was thicker, and the corneal refractive power was higher. In ROP group, the corneal refractive power of 48 right eyes in zone Ⅱ subgroup and 37 right eyes in Zone Ⅲ subgroup were (43.92±0.78) D and (43.39±1.05) D respectively, and the spherical equivalent were (2.08±0.95) D and (2.52±1.12) D respectively. The corneal refractive power of zone Ⅱ subgroup was higher and the spherical equivalent was smaller, and the differences were statistically significant (all P<0.05). Multiple regression analysis showed that birth weight, gestational age and corneal refractive power were the influencing factors of spherical equivalent (P<0.01). The results of Pearson correlation analysis showed that the gestational age (r=0.182), birth weight (r=0.223) and corneal refractive power (r=-0.125) of premature infants were closely related to the spherical equivalent (all P<0.05). Conclusions: In premature infants, the larger spherical equivalent is related to greater gestational age and heavier birth weight. The refractive parameters of mild ROP are characterized by shallow anterior chamber, thick lens, high corneal refractive power and small spherical equivalent. The spherical equivalent is closely related to the development of ROP. (Chin J Ophthalmol, 2021, 57: 353-357).