Year : 1995 | Volume
: 43 | Issue : 3 | Page : 123--126
The incidence of retinopathy of prematurity in a neonatal care unit
Rohit Charan1, MR Dogra1, Amod Gupta1, Anil Narang2,
1 Departments of Ophthalmology Postgraduate Institute of Medical Education & Research, Chandigarh., India
2 Department of Neonatology, Postgraduate Institute of Medical Education & Research, Chandigarh., India
M R Dogra
Department of Ophthalmology, Postgraduate Institute of Medical Education & Research, Chandigarh 160 012
In India, with advancement in neonatal care units, a large number of low-birth weight premature babies are now surviving and are at risk of developing retinopathy of prematurity (ROP). However, there are not enough reports on the incidence of ROP in this country. To determine the incidence of ROP in a prospective manner, 165 babies weighing ≤ 1700 gm over a period of one year were examined. An incidence of 47.27% of ROP at the mean age of 7.21 ± 0.3 weeks of life was detected. The maximum stage reached was stage 1 in 28 (16.97%), stage 2 in 29 (17.58%), stage 3 in 19 (11.52%) and stage 4b in 2 (1.21%) babies. Plus disease was present in 17 (10.3%) babies. Babies with lower birth weights and lower gestation age at birth had a significantly higher (p = < 0.05) incidence of ROP. However, the difference in mean birth weight and gestation age at birth for various stages of ROP was not significant (p = > 0.05). Thus, we recommend screening for all babies weighing ≤ 1700 gm.
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Charan R, Dogra M R, Gupta A, Narang A. The incidence of retinopathy of prematurity in a neonatal care unit.Indian J Ophthalmol 1995;43:123-126
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Charan R, Dogra M R, Gupta A, Narang A. The incidence of retinopathy of prematurity in a neonatal care unit. Indian J Ophthalmol [serial online] 1995 [cited 2021 Dec 5 ];43:123-126
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Retinopathy of prematurity (ROP) is a disorder of the developing retinal blood vessels in the premature infant retina. The key pathological change in ROP is peripheral retinal neovascularisation. This may regress completely or leave sequelae from mild myopia to bilateral total blindness. The condition was first described by Terry in 1942 as retrolental fibroplasia. In the following decade, the disease reached epidemic proportions, which was later controlled by restriction of oxygen use. ROP again reached epidemic proportions in the 1970s due to development of modern intensive care units which resulted in the increased survival of low-birth weight premature infants., The international classification of ROP has helped in uniform documentation and staging of ROP., Recently, the multicentre trial on cryotherapy for ROP has demonstrated that cryotherapy of the peripheral retina reduces by half the incidence of an unfavourable outcome and this has enewed the interest in screening for ROP.
In India, with the development of neonatal intensive care units, premature infants with extremely low birth weights are surviving and are at highest risk of developing ROP. However, the incidence of ROP in low-birth weight babies in India is not often reported and there are no recommended screening strategies for ROP surveillance. To determine the incidence of ROP, we performed a prospective study in infants with birth weight ? 1700 gm, admitted to the neonatal unit of our hospital, over a period of one year. The significance of birth weight, gestation age, multiple births and gender in relation to the incidence of ROP were also studied.
MATERIALS AND METHODS
One hundred and sixty-five babies with birth weight ≤ 1700 gm, admitted to the neonatal unit of the Postgraduate Institute of Medical Education and Research, Chandigarh, in 1993 were enroled into the study. The ophthalmologic examination commenced at 6 weeks of life and/or at discharge from the neonatal unit, whichever was earlier. The purpose of the initial examination at discharge was to detect and enrol the babies with ROP. In cases where the retina was not fully vascularised, ophthalmologic examination was repeated every 2 weeks until full vascularisation. If ROP was present, weekly examinations were carried out. The end-stage for ophthalmologic examination was nonproliferating retinopathy or fully regressed disease (spontaneous or with treatment).
The pupils were dilated using phenylephrine 2.5% and cyclopentolate 0.5%. All-pupil binocular indirect ophthalmoscope and + 20 D lens were used for examination. The preferred method of ocular examination was to prise open the infant's lids and to use low intensity of illumination to reduce blepharospasm. The oculocephalic reflex was used, by rotating the infant's head, to visualise the required area of the retina and to reduce Bell's phenomenon. The scleral indenter was used to rotate the eyeball in cases where the infant lid speculum was also required.
Retinal vascular changes were recorded in accordance with the international classification of ROP.[4, 5] Data on the premature infant's gender, multiple births, birth weight and gestation age at birth were recorded and analysed using the chi-square test, analysis of variance and t-test. Prior to commencement of the study, a month-long pilot study was carried out by the two principal examiners (MRD and RC) to standardise examination techniques and, the results were compared.
The birth weights of the 165 babies ranged from 820 to 1700 (mean ± SE, 1382.84 ± 17.8) gm and the gestation age varied from 26 to 40 (32.47 ± 0.2) weeks. All the 18 (10.90%) cases of multiple births in this study were twins. There were 108 (65.45%) males and 57 (34.55%) females. ROP was documented in 78 (47.27%) babies. The maximum stage of ROP reached was stage 1 in 28 (16.97%), stage 2 in 29 (17.58%), stage 3 in 19 (11.52%) and stage 4b in 2 (1.21%) babies. The mean age at which acute ROP was first detected was 7.21 ± 0.3 weeks of life.
Of the 78 babies with ROP, the temporal retina alone was involved in 44 (56.41%), while the nasal retina alone was involved in 17 (21.18%) babies. Simultaneous nasal and temporal retinal involvement was seen in 18 (23.07%) babies. No baby was found to develop ROP involving only 6 or 12 o'clock at the onset of the disease. Of the 19 babies with stage 3 ROP, 8 (42.10%) had greater than 5 continuous clock hours involvement.
Zone III involvement never progressed beyond stage 1 disease, while Zone I disease progressed to stage 3 in all cases. Zone II disease progressed to stage 3 in 15 (78.95%) cases. ROP was found to be symmetrical within one stage in all the cases. Plus disease was found in 17 (10.30%) babies. All infants with plus disease had a birth weight less than 1500 gm. Babies with plus disease had posterior pole venous engorgement and arteriolar tortuosity. Five (29.41%) of the babies with plus disease had pupillary rigidity. Stage 2 disease in 4 babies and stage 3 disease in 13 babies were associated with plus disease. None of the babies with stage 1 ROP had plus disease.
There were no statistically significant differences (p = > 0.05) between the incidence of ROP and gender or multiple births. Infants who developed ROP had mean birth weight (1284.95 ± 26.9 gm) and mean gestation age (31.49 ± 0.3 weeks) significantly lower (p = < 0.001) than the mean birth weight (1470.60 ± 19.4 gm) and gestation age (33.41 ± 0.3 weeks) of babies who did not develop ROP. Of the 20 babies with birth weight ranging from 750 to 1000 gm, 18 (90%) developed ROP compared to 14 (25.92%) of the 54 babies weighing between 1501 and 1700 gm [Figure:1]. The various subgroups, each with a lower birth weight, had a significantly higher (p = <0.05) incidence of ROP. However, there was no significant difference (p = >0.005) between babies weighing 1001 to 1250 gm and those weighing 1251 to 1500 gm [Table:1]. Babies with lesser gestation age at birth had a higher (p<0.05) incidence of ROP [Figure:2].
The mean birth weights were 1343.50 ± 41.5 gm for stage 1,1271.52 ± 46.2 gm for stage 2,1233.4 ± 56.9 gm for stage 3 and 1150 ± 150 gm for stage 4. Mean gestation age at birth were 32.07 ± 0.5 weeks for stage 1, 37.41 ± 0.4 weeks for stage 2, 31.0 ± 0.6 weeks for stage 3 and 29.0 ± 1.4 weeks for stage 4. Babies with higher stages of ROP had lesser birth weights. However, the analysis of variance showed that the difference was not statistically significant (p = >0.05). Similarly, the incidence of various stages of ROP, analysed for significance related to the gestation age at birth, was not statistically significant (p >0.05).
The incidence of ROP is on the increase due to improved survival of low-birth weight babies. Screening of low-birth babies is essential to detect ROP.
Palmer has recommended screening examination at 7 to 9 weeks of age. The American Academy of Paediatrics has recommended the same between 7 and 8 weeks postpartum. In the Multicentre Trial CRYO-ROP Study, infants were first examined between 4 and 6 weeks after birth. In our study, we performed the initial examination at 6 weeks of life and/or at discharge. The mean age at which ROP was first detected was 7.21 ± 0.3 weeks of life. Stannard et al have noted the futility of examination at very early age as the view of the peripheral retina is difficult. During the pilot survey, i.e., before commencement of this study, we had difficulties in visualisation of peripheral retina and no evidence of ROP was seen in infants less than 4 weeks of life.
Individual preferred methods exist as regards to medication for pupillary dilatation,, and use of speculum or scleral depressor. While no standard technique exists, we found dilatation with phenylephrine 2.5% and cyclopentolate 0.5% was adequate, so also use of the infant speculum and scleral indenter on anaesthetised (xylocaine 2%) conjunctive. The scleral indenter was used more for rotation than for indentation of the globe.
The incidence of ROP in various Western studies has been reported to vary from 21 to 65.8%.,, In our study, we found the incidence of ROP to be 47.27% [Table:2]. However, earlier reports cannot be compared to our study due to different selection criteria, methods of examination and absence of use of the international classification of ROP, as suggested by the CYRO-ROP Study Group.
We found a higher incidence of horizontal meridian involvement than the vertical meridian alone. Temporal retina alone was found to be involved more commonly as compared to nasal retina. This has also been reported by other investigators[15,21] In our study, the posterior retinal involvement was more often associated with more advanced disease. Fielder et al have also reported similar observations. As in the CRYO-ROP study, we found no statistically significant difference in the incidence of ROP with gender or multiple births.
While the babies who developed ROP in our study population had significantly lower birth weight and gestation age (p = <0.05), we still were not able to predict which of these babies would eventually develop severe ROP (stages 3 and 4). The CRYO-ROP study also did not report a significant difference in the mean birth weight for the various stages of ROP. These facts highlight the importance of surveillance programme for all babies in our study population.
Our study demonstrates the incidence of ROP in low-birth weight babies which is comparable with most Western reports. Further prospective and multicentre studies are needed to estimate the true incidence of ROP in India.
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