Abstract
The effect of ocular protection on the incidence of retinopathy of prematurity was tested in 188 newborns weighing less than 1600 g in a randomised controlled trial. No effect of ambient light reduction on the incidence of retinopathy of prematurity was shown.
Keywords: retinopathy, prematurity, light
Clinical studies conducted to date have yielded conflicting results on the effects of light on retinopathy of prematurity (ROP).1,2,3,4 Phelps and Watts5 performed a Cochrane Review and meta‐analysis, reviewing all papers published to date (and included the present study as “in progress”). They concluded that it is unlikely that the ambient luminosity affects the incidence of ROP, but stressed the large confidence intervals in the combined data, which were due to the small number of threshold or pre‐threshold diseases.5
This study concurs with the final outcomes of the previous studies and yields additional evidence that exposure to light does not affect the incidence of ROP.
Methods
All infants born at a gestational age of less than 32 weeks and or a birth weight less than 1600 g at two neonatal intensive care units were included. They were randomised to two groups, trial and control, and stratified by birth weight (>1000 g or <1000 g). Infants in the trial group received ocular protection against the ambient light on both eyes, from birth until 35 weeks of corrected gestational age. Infants in the control group did not receive ocular protection and were kept under the regular light conditions.
Indirect ophthalmoscopy was performed within four to six weeks of birth and thereafter every one or two weeks. The diagnosis of ROP was confirmed at at least two examinations according to the criteria of the CRYO‐ROP study.6 The ambient light was measured using an ICEL digital light meter, model LD‐500 (Parana, Brazil).
Statistical analysis was performed using the χ2 test, Student's t test, and logistic regression.
The study protocol was approved by the institution review board for ethical conduct in humans, and written informed consent was obtained from the parents.
Results
A total of 226 newborns met the requirements for admission to the study and were randomly allocated to the trial or control group. During this period, two parents refused to participate in the study, 33 babies died, two infants were transferred, and one infant did not complete the allocation procedure properly. The final breakdown was 95 newborns in the trial group and 93 in the control group.
The mean luminosity was 383 lux (range 188–540).
There were no significant differences between the groups with regard to body weight, gestational age, and the main maternal and neonatal morbidities (table 1).
Table 1 Characteristics of the study groups.
| Control (n = 93) | Trial (n = 95) | p Value | |
|---|---|---|---|
| Birth weight | 1137 (324) | 1194 (273) | >0.05 |
| Gestational age | 29.7 (2.3) | 30.2 (2.3) | >0.05 |
| Male infants | 61 | 48 | >0.05 |
| Maternal steroids | 42 | 37 | >0.05 |
| Normal delivery | 34 | 33 | >0.05 |
| HMD | 50.5 | 42 | >0.05 |
| PDA | 26 | 27 | >0.05 |
| Suspected sepsis | 59 | 55 | >0.05 |
| Confirmed sepsis | 29 | 23 | >0.05 |
| Apnoea | 77.4 | 72 | >0.05 |
Values are mean (SD) or percentages.
HMD, Hyaline membrane disease; PDA, patent ductus arteriosus.
There were no significant differences with regard to respiratory assistance between the groups. Mechanical ventilation was administered for 293 (509) hours to the trial group compared with 259 (103) hours to the control group (median 90 v 103 hours), continuous positive airway pressure for 140 (20) v 161 (18) hours (median 48 v 84 hours), and oxygen 23 (33) v 23 (29) days (median 6 v 12 days).
A total of 368 ophthalmological examinations were performed during the period of the study with a mean (SD) of 1.96 (1.24) per baby.
Table 2 shows the frequency of confirmed retinopathy, grade 3 and 3+ (pre‐threshold disease).
Table 2 Incidence of retinopathy of prematurity.
| Control group | Trial group | p Value | |
|---|---|---|---|
| Absent | 50/93 (54) | 51/95 (54) | >0.05 |
| Grades 1 & 2 | 36/93 (39) | 37/95 (39) | >0.05 |
| Grades 3 & 3+ | 7/93 (7) | 7/95 (7) | >0.05 |
| Cryo/Laser | 6 (6) | 5 (5) | >0.05 |
| Total | 43/93 (46) | 44/95 (46) | >0.05 |
Values in parentheses are percentages.
Cryo/Laser, cryotherapy or laser therapy for retinopathy.
To control for possible confounding variables, we conducted a logistic regression analysis adjusting for the time of exposure to oxygen, sex, gestational age, birth weight, and suspected or confirmed sepsis. The odds ratio and confidence intervals for eye protection were 1.24 (0.61 to 2.48) (p = 0.55).
Discussion
It is difficult to compare the results of this study with those reported by initial clinical studies that investigated the role of ambient light on the development of ROP such as those conducted by Glass et al,1 Ackerman et al,2 and Seiberth et al3 because of the differences in methodology, population, and study design. Our results are very similar to those of Reynolds et al,4 differing only in the population of newborns admitted (<1600 g v <1250 g). For this reason, the incidence of ROP in our study was lower: 46% v 58%. If we stratify the data using the same birthweight bracket (<1250 g), our ROP incidence was 63% in the trial group and 60% in the control group, which is very close to the values found by Reynolds et al.
What is already known on this topic
Known risk factors for retinopathy of prematurity are low birth weight and oxygen exposure
Light exposure has been studied as a possible risk factor
What this study adds
Further evidence is provided that light reduction does not decrease the incidence of retinopathy of prematurity
The results of this study combined with published data provide strong evidence that reduction of ambient light does not have any effect on the incidence of retinopathy in infants with very low birth weight.
Acknowledgements
We thank Dr Dale Phelps for help and advice in writing this manuscript.
Footnotes
Competing interests: None declared.
Ethics approval: Ethics committe approval was obtained for this study.
References
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