Progression to type 1 ROP occurs in about a week or more in most eyes with type 2 ROP

Researchers analyzed data from the Early Treatment for Retinopathy of Prematurity (ROP) Study to examine the timing and frequency of progression of eyes with type 2 ROP (based on the clinical algorithm) to type 1 ROP. They included in their analysis 294 eyes diagnosed with low-risk prethreshold ROP with type 2 characteristics at the first examination. They were examined every two to four days for at least two weeks.

Among them, 65 eyes (22.1 percent) progressed to type 1 disease. The mean time between the first diagnosis of type 2 ROP and the diagnosis of type 1 ROP was nine days (median,  seven days). Of the 217 eyes with type 2 ROP that had an examination in less than seven days, 25 (11.5 percent) were diagnosed with type 1 ROP in less than seven days. Of the 200 eyes that continued to have type 2 disease at the first follow-up examination and underwent a subsequent examination, 24 (15.7 percent of the 153 eyes that had an examination in less than seven days) developed type 1 ROP in less than seven days. The risk of progression from type 2 to type 1 in less than seven days was greatest between 33 and 36 weeks postmenstrual age, regardless of zone of retinopathy.

The authors concluded that type 1 ROP can be identified with weekly examinations in most eyes with initial diagnosis of type 2 ROP, although a small subset progresses to type 1 in less than seven days. However, to define more precisely the timing of progression of eyes with type 2 ROP to type 1 ROP, more frequent and rigidly controlled follow-up ROP examinations would be required. Thus, the results of the present study must be interpreted cautiously with this limitation in mind.