Novel ultrasound-based classification of retinal funnel patterns in stage 5 retinopathy of prematurity

Ultrasound (USG) B-scan is a useful investigation to determine the retinal funnel configuration in stage 5 Retinopathy of Prematurity (ROP) and assess the feasibility of surgical intervention, and prognosis. Typically open-closed terms (closed-closed, open-closed, closed-open, open-open funnels) have been used to describe the retinal funnel in the anterior-posterior compartments [1, 2]. Stage 5 ROP surgery necessitates an anterior surgical approach for safe instrument entry [3], with best outcomes observed with open-open funnels [4]. The latest ROP classification (ICROP 3) subdivides stage 5 ROP into three types (5 A, 5B, 5 C) but does not offer additional clarity about retinal funnel patterns. Shapiro et al observed double tent-shaped, chevron-based and star-shaped retinal detachments [5], but these have not been validated by others.

The I pattern has a closed band-like appearance which may not be operable; might have large peripheral avascular areas and closely mimics persistent foetal vasculature (PFV) stalks. The Y pattern was most common (26.3%), with a posterior closed funnel; the lesser the vertical height of the posterior closed funnel, the better surgical outcome might be expected. The V pattern is also common (24.6%) and surgical outcomes might depend on how narrow the angle of V is and the extent of internal echoes that signifies density of membranes and adhesions. The O pattern shows a large central area that is loosely open with limited peripheral anterior attachments and may have good surgical outcomes. The X pattern (6.7%) suggests a central adhesion, with a shallow detached peripheral retina that might attach if traction is suitably relieved. The U pattern might have clear fundus view with peripheral circumferential anterior retinal traction (e.g. stage 5 A ROP), and further surgery might not be beneficial. VH (vitreous haze) pattern is confusing yet common (23.3%), resembles a ‘vitreous haemorrhage’ like pattern, however, underlying V or other pattern maybe masked by extensive subretinal echoes (possible subretinal crystals) and may signify poorer outcomes. A transition from U to O to V to Y to I may represent a progressive funnel closure, making surgery difficult.