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after institutional review board approval , we did a retrospective chart review of infants 1500 g birth weight and treated for aprop between january 2006 and december 2009 .
the neonatal intensive care unit at our institute is a level iii nursery , which also caters infants born at other centers ( outborn ) .
aprop was diagnosed in accordance with the international classification of rop and documented by detailed retinal drawings and retcam ( clarity msi , pleasanton , california , usa ) .
we completed a chart review that retrieved various parameters including birth weight , gestational age , setting of birth ( inborn / outborn ) , level of nursery care ( level i nursey : basic level nursery , level ii : specialty services like mechanical ventilation , level iii sub - specialty care including sustained life support ) , neonatal illnesses , and oxygenation .
we excluded infants with hydrocephalus , as this condition leads to an exaggerated birth weight .
characteristics of rop including the zone , pattern of neovascularization , and atypical features were noted .
all infants underwent confluent laser ( less than half burn width apart ) application with either a diode laser or 532 nm laser delivered through the indirect ophthalmoscopic system .
we noted details of laser treatment including postconceptional age at treatment , number of spots , number of laser sittings , time to regression , and outcome .
the criteria for unfavorable outcome at 6 months were : ( 1 ) retinal detachment ( stage 4a/4b/5 ) , ( 2 ) falciform fold involving the macula , and ( 3 ) a retro - lental tissue / mass obscuring the view of the posterior pole .
sixteen infants 1500 g birth weight underwent laser photocoagulation for aprop during the study period .
disease characteristics of infants developing aprop the mean birth weight and gestational age were 1791.27  281.86 g ( range , 1500 - 2300 g ) and 30.7  1.03 weeks ( range , 29 - 32 weeks ) , respectively .
all infants were outborn and referred from level i / ii accredited nurseries , which had a limited level of neonatal care with paucity or nonavailability of saturation monitors and oxygen blenders .
duration of oxygen exposure was known for 11 infants and ranged from 7 to 23 days .
systemic risk factors in infants  1500 g developing aprop ( n=14 ) * twenty - nine eyes of 15 infants developed aprop .
of the 29 eyes , 10 ( 34.5% ) had zone 1 and 19 ( 65.5% ) had posterior zone 2 disease .
fundus photographs from a male infant weighing 1500 g at birth and 29 weeks of gestation demonstrate aprop in posterior zone 2 and regression following confluent laser photocoagulation .
( a ) fundus photograph prior to laser photocoagulation demonstrates plus disease and flat new vessels in posterior zone 2 .
( b ) fundus photograph at 37 weeks shows complete regression fundus photographs from a male infant weighing 1875 g at birth and 32 weeks of gestation demonstrate aprop in zone 1 with extensive brush like proliferation projecting into the vitreous and covering the optic disc and posterior pole in right eye ( a ) and left eye ( b ) , respectively .
both eyes had an unfavorable outcome after laser fundus photographs from a male infant weighing 1990 g at birth and 30 weeks of gestation demonstrate aprop in posterior zone 2 and large vascular loops .
( a ) fundus photograph prior to laser demonstrates plus disease , flat new vessels and hemorrhages in posterior zone 2 .
( b ) the nasal aspect of same eye demonstrates a large vascular loop ( block arrow ) enclosing a grayish avascular retina ( arrow ) .
( d ) the nasal aspect of same eye shows laser scars inside the vascular loop the mean post conceptional age at laser treatment was 35.2  1.54 weeks ( range , 33 - 39 weeks ) .
the mean number of spots were 2323.83  1211.20 ( range , 840 - 5210 ) .
of the 29 eyes , 22 ( 75.9% ) eyes had complete regression after laser .
the mean time to regression was 6.14  2.05 weeks ( range , 3 - 10 weeks ) .
seven ( 24.1% ) eyes had an unfavorable outcome ( stage 5 : two eyes , stage 4a : two eyes , cataract : two eyes , vitreous hemorrhage : one eye ) .
one eye with stage 5 underwent lensectomy vitrectomy with an unfavorable outcome . the other eye with stage 5
both eyes of an infant had localized ( 2 clock hours ) stage 4a detachments which remained stable until a follow - up of 34 months .
overall , a complete regression was achieved in 25 ( 86.2% ) of the 29 eyes .
various studies from the west and japan describe aprop in infants < 30 weeks of gestational age and < 1000 g birth weight . however , recent studies from india report aprop in older and heavier infants . in a recent study from north india ,
15.91% infants developing aprop had a birth weight above 1500 g. the reported risk factors for zone 1 aprop include extreme prematurity , disruption of vasculogenesis , and a low platelet count .
a recent study has observed the use of supplemental unblended oxygen in heavier infants developing aprop .
most of the infants in the present series had multiple co - morbidities and received supplemental oxygen in centers with poor neonatal care .
it is plausible that early and excessive exposure to unmonitored oxygen therapy may lead to aprop - like morphology in these infants .
however , the present study is too small to prove causal association of any risk factor with aprop in heavier infants .
aprop in heavier infants differs in certain aspects from disease seen in extremely low birth weight premature infants [ table 3 ] .
first , there is a preponderance of posterior zone 2 aprop with more mature central vasculature as compared with poorly developed vasculature in zone 1 aprop .
second , vessels extend for a considerable distance into the nasal retina forming large loops and enclosing an underlying avascular retina .
finally , we did not observe relentless fibrovascular proliferation after laser treatment , which might limit outcomes in typical aprop .
clinical features , risk factors and outcomes for various types of rop the present study is retrospective and lacks a control group .
a prospective study is difficult , given the fact that infants come from different centers . in conclusion , aprop may be seen in infants  1500 g birth weight .
further studies should evaluate the risk factors , pathogenesis , and genetic mechanisms for aprop in these infants .
in this retrospective case series , we report the spectrum and outcomes of aggressive posterior retinopathy of prematurity ( aprop ) in infants 1500 g birth weight . 
 twenty - nine eyes of 15 infants are included . 
 all infants were referred from level i or ii nurseries , received supplemental unmonitored oxygen for prolonged duration ( > 1 week ) and had multiple systemic co - morbidities . 
 of the 29 eyes , 10 ( 34.5% ) had zone 1 and 19 ( 65.5% ) had posterior zone 2 disease . 
 twenty - five ( 86.2% ) eyes had flat neovascularization and 4 ( 13.8% ) eyes had brush like proliferation . 
 we noticed large vascular loops in 10 ( 34.5% ) eyes . 
 after confluent laser photocoagulation , 22 ( 75.9% ) eyes had a favorable outcome . 
 the study concludes that aprop in heavier ( 1500 g birth weight ) premature infants occurs mostly in posterior zone 2 with flat neovascularization and atypical features like large vascular loops . supplemental unmonitored oxygen for prolonged duration and multiple systemic co 
 - morbidities could be a contributing factor .