Cryotherapy for retinopathy of prematurity: a MRI study of the surgical-anatomical relationship of the neonatal conjunctival fornices to the globe.

Abstract

To demonstrate the surgical-anatomical relationship of the neonatal conjunctival fornices to the globe in order to ascertain whether adequate cryotherapy is possible in infants with stage 3 retinopathy of prematurity using a trans-scleral approach without opening the conjunctiva. Magnetic resonance (MR) scans of the orbit were performed on an adult and an infant of 38 weeks post-conceptual age with maximal posterior placement of a MR-compatible replica of the Schulenburg cryoprobe in the nasal and temporal aspects of the globe. In the infant MR scan, the scleral indentation produced by the probe was anterior to the equator on the nasal side and at, or just anterior to, the equator on the temporal side. Nasally, the scleral indentation reached only the more anterior part and not the posterior part of zone 2 and none of zone 1. Temporally, the scleral indentation reached the central part of zone 2 but not the posterior part of zone 2 or zone 1. The findings suggest that adequate cryotherapy with a trans-scleral approach without opening the conjunctiva is unlikely to be achieved in the more immature neonate with posteriorly located retinopathy of prematurity. To permit access of the cryoprobe to the more posterior part of the globe, one radial conjunctival incision from the corneal limbus in each quadrant may be required to achieve adequate ablation of the posterior non-vascularised retina in these high-risk infants.