Optic disc photos may be unnecessary when using a scanning system

In some circumstances, it may be unnecessary to obtain images simultaneously with a confocal laser scanning system and optic disc photography, suggests a new study.

Key Points

Singapore-Omitting the use of optic disc photographs when using a confocal laser scanning system (Heidelberg Retinal Tomography, Heidelberg Engineering) does not appear to affect the accuracy of measuring the outputs and could streamline the logistics of conducting population-based studies as well as result in cost savings.

"The [scanning system] is becoming faster, and it's a tool that is used in many population-based studies," said Seng Chee Loon, FRCS(Ed), MMed, a glaucoma specialist and epidemiologist at National University Hospital, Singapore. "Population-based studies usually involve numbers in the thousands, hence, any logistical problems that you might see would be magnified. If there's any way that we can save on some form of logistics or cut down on one step, that could lead to a lot of savings on [staffing] or other costs."

Eliminating optic disc photography could be one such step. Dr. Loon recently reported the outcomes of a study in which he and colleagues in Singapore, London, Sydney, and Melbourne evaluated the measurement of optic disc morphology using the scanning system with and without the aid of optic disc photographs.

All contour lines were drawn by the same researcher on two occasions. The first drawing was done without the aid of optic disc photographs. The second drawing, made 2 days later, was done with the three-dimensional rotation assessment and digital monoscopic optic disc photographs.

The scanning system measurements made with and without optic disc photography were very similar, Dr. Loon said. For global disc area readings, the different between the mean readings was 0.67 mm2, and the interclass correlation (ICC) was 0.81 (95% confidence interval [CI], 0.73 to 0.86). The mean difference in readings for global cup-to-disc ratio was 0.03, and the ICC was 0.86 (95% CI, 0.80 to 0.90). The ICCs were high across most of the readings, with the exception of rim volume. The ICC for that reading was 0.57 (95% CI, 0.43 to 0.69).

The high correlation between measurements made with and without the photographs suggests that at least one piece of equipment could be left behind when performing large-scale glaucoma studies in the field, he said.

Much of the work that has been done previously with the scanning system recommended optic disc photography, based on a belief that it improves accuracy.

"But evidence-based medicine shows that you can do away with it and be just about as accurate," Dr. Loon concluded.

In addition to his position in Singapore, Dr. Loon is affiliated with the Department of Ophthalmology, Centre for Vision Research, Westmead Millennium Institute, University of Sydney, New South Wales, Australia.

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