Sir,

A limitation of the use of RetCam imaging for Retinopathy of Prematurity (ROP) screening is the inability to determine whether a temporally placed ROP ridge is in Zone 2 or Zone 3.1 Observation of the retinal vasculature close to the nasal ora serrata is necessary to determine whether disease is in zone 2 or zone 3,2 and this is difficult to achieve with RetCam imaging.1 We have performed a pilot study to determine the location of the junction of Zone 2 and Zone 3 in the temporal retina of RetCam images.

In a series of routine ROP screening examinations in our nursery, video indirect ophthalmoscope with scleral indentation examination of the nasal ora seratta was used to identify eyes in which ROP was located at (within 1 disc diameter), or near to (1–2 disc diameters) the junction of zone 2 and zone 3. RetCam images of these eyes, with the optic disc placed at the nasal edge of the image were recorded. The distance from the temporal edge of the image to the temporal ROP ridge was measured, expressed in disc diameter units. A line through the optic disc and bisecting the temporal arcades was used to orientate the images (Figure 1). Any small amount of offset of the position of the optic disc relative to the nasal edge of the RetCam image was corrected when making measurements on the temporal side.

Figure 1
figure 1

RetCam image of an eye with ROP at the junction of Zone 2 and Zone 3. The temporal ROP ridge is positioned 1.5 disc diameters posterior to the temporal edge of the image.

Full size image

Forty-eight eye examinations (26 patient screening examinations) in 13 infants were analysed. The median gestation was 27 weeks (range 24–29 weeks), the median birth weight 810 g (range 650–1295 g). Nine of the infants were female. The junction between zone 2 and zone 3 was reached at a median time of 38 weeks (range 35–42 weeks) post-menstrual age (PMA). The junction of zone 2 and zone 3 temporal retina was found to lie 1.3–2.7 (median 1.8 disc diameters) disc diameters posterior to the temporal edge of the RetCam image of the temporal retina (Table 1).

Table 1 Position of the ROP ridge in the temporal retina, relative to the temporal edge of the RetCam image
Full size table

It is likely that a RetCam examination that excludes plus disease, or active ROP in the part of the retina visualised using RetCam examination, including a view of the temporal periphery, is in general sufficient to determine whether treatment-requiring disease is present,3 and whether further ROP screening examinations are necessary. The nasal retina should also be examined.