Sir,

We thank Young-Hoon Park1 for his interest in our article entitled ‘Correlation of visual recovery with macular height in macular-off retinal detachments’. In reply to his first point, the retina was measured after it ceased to move after postural change in both supine and sitting position respectively. We agree that standardization of positions of ultrasound probes should be done for studies and this was the case in our study protocol.

Our ultrasonic measurements were done using the CineScan 10 MHz probe. For accurate localization the probe was placed directly on the cornea after topical anaesthesia. The axial scan was done with the white line on the probe, placed in the direction of the macula so that both macula and optic nerve were visible in the axial scan (Figure 1). Measurements were taken when the correct disc configuration was obtained, ie, when the disc did not appear oblique or tilted on ultrasound. This method gives a fairly accurate reference point (disc and macula) within the scope of two-dimensional B-scan ultrasound.

Figure 1
figure 1

Diagrammatic representation of the position of the probe on the eye in order to visualize the macular area.

Full size image

We further standardized our measurements using markers to measure at a distance 4 mm from the centre of the disc temporally. From that point a digital caliper was used to measure the perpendicular distance between the retinal pigment epithelium and the outer neurosensory detached retina.

Although the mean macular height was higher in the sitting group (2.42+1.2 mm) than in the supine group (2.39+1.0 mm), in our study there was no significant difference according to posture (t test, P=0.9).2 There are limitations to the accuracy of measurements with two-dimensional B-scan ultrasonography; however, standardization of measurements for studies improves the validity of the results.