Cryosurgery for acute retinopathy of prematurity: factors associated with treatment success and failure.

Cryosurgery for stage 3 plus acute retinopathy of prematurity (ROP) increases the probability of disease regression, but up to 25% of eyes may progress to retinal detachment and blindness in spite of treatment. In a series of 37 eyes in 23 patients treated at the Hammersmith Hospital an overall 75% of eyes reached a favourable outcome. We present these results in detail and analyse the apparent causes of treatment failure. Poor anatomical results (total retinal detachment and traction detachment involving the macula) were associated with inappropriate cryoprobe design and with zone 1 and rush-type disease. Poor functional results in the presence of a largely flat retina (marked macular ectopia and high myopia) appeared to be associated with delayed treatment during the period of evolution of the stage 3 lesion, and with the appearance of a more highly differentiated vascular shunt with early localised forward vitreous invasion. Suggestions for the refinement of existing gradings of acute ROP are made.