3 May 2008
RE: AP-ROP IN AN INFANT WITH MINIMAL OXYGEN EXPOSURE
Buksh et al. report development of severe retinopathy of prematurity (ROP) in a 700 gm preterm baby with minimal oxygen exposure.1 The patient reported in the case is an extremely low birthweight infant (weight less than 1000 gm). Extremely low birthweight is proven to be the most important risk factor for development of ROP in various studies.2,3
The ROP disease spectrum seen in these babies is entirely different from more mature low birthweight babies. Schulenburg et al. reported variable morphological pattern of ROP seen in these extremely low birthweight infants.4 In our experience also, we found that they do not follow the typical staging pattern seen in mature babies with ROP.
The specific features of ROP seen in extremely low birthweight infants are no typical demarcation line or ridge is seen between vascular and avascular retina. The shunting vessels or demarcating vessels (communication between temporal arcade vessels) are commonly seen in these babies. The site of demarcating vessel is the site of future new vessel formation. The neovascularisation seen in these babies is usually seen as filiform tangles with reduced calibre than the mature new vessels seen with ROP in mature babies.
Most of these babies present with zone 1 or posterior zone 2 ROP. Flynn et al. reported two distinct pathogenetic mechanisms lying under zone 1 and zone 2 ROP.5 They described zone 1 disease as more severe form occurring frequently in low birthweight infants and as relatively insensitive to laser photocoagulation.
Diagnosis of plus disease is difficult as the retinal vascular calibre is less compared with mature babies. One may observe corkscrew pattern of retinal vessels in the entire retina. This is the usual sign of plus disease, we observe in these babies.
Irrespective of gestational age, we prefer initial screening for ROP at 3–4 weeks of chronological age in these extremely low birthweight babies. From then we follow them at less than 1-week intervals (3 days–1 week). We perform immediate laser photocoagulation in these babies in the presence of demarcating vessels (can term as stage I), as this is the site of future new vessel formation. We do not wait until the frank signs of plus disease like haemorrhages to appear. They usually require multiple sessions of laser photocoagulation to ablate the large avascular retina. Multiple laser sessions are also required as these babies are more prone to apnoea attacks.
To conclude, we feel frequent follow up (less than a week intervals), understanding the unique disease pattern of extremely low birthweight infants and timely laser photocoagulation (usually multiple sessions) within the crucial window period are necessary to avoid the avoidable blindness of ROP.