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Patricia Cobb, Michael B Yang; Nonlinear association of average day length during early gestation with severe retinopathy of prematurity outcome. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4583.
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We previously reported that higher average day length (ADL) during early gestation was associated with a lower likelihood of severe retinopathy of prematurity (SROP) outcome. The purpose of this study is to analyze whether the association of ADL with SROP was linear throughout the range of ADL.
684 eyes of 343 premature infants (401-1250 g birth weight (BW)) admitted to the University of Cincinnati Medical Center from 1998 to 2002 were included. Multiple logistic regression with generalized estimating equations to account for inter-eye correlation was performed including variables of BW, gestational age, per capita income in the mother's residence zip code, multiple birth, race, gender, and ADL during the first 90 days after conception in Cincinnati, Ohio, USA (range 9.74-14.62 h; divided into quintiles). The outcome variable was SROP which developed in 76 eyes and consisted of classic threshold ROP, type 1 ROP in zone I, and treated type 1 ROP in posterior zone II.
A nonlinear association of ADL with SROP was found. Eyes of infants with the lowest 2 quintiles of ADL during the first 90 days after conception (9.74-10.29 h and 10.30-11.64 h) were respectively associated with a 4.4-fold (95%CI: 1.1-18.4; P=0.042) and a 4.0-fold (95%CI: 1.05-15.6; P=0.043) increase in the likelihood of developing SROP as compared with the highest quintile of ADL (13.94-14.62 h). The other quintiles of ADL were not significantly associated with an increased likelihood of SROP as compared with the highest quintile of ADL. Models of SROP outcome using the subset of 468 “any” ROP eyes and 146 prethreshold ROP eyes yielded similar results. Similar results were obtained when average daily solar insolation, which measures light intensity reaching the earth's surface, was substituted for ADL.
The nonlinear association of ADL with SROP may be consistent with a saturation affect typically found in biological systems. These findings may provide added support for a previously described fetal mouse model of melanopsin-dependent light response in retinal vascular development and may imply a minimum threshold of light exposure necessary to lower the risk of SROP.
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