A recent study demonstrated that vertical cup-to-disc ratios measured by optical coherence tomography (OCT), Heidelberg retina tomography (HRT) and stereoscopic photography did not agree with each other, and these discrepancies extended to the calculated risk of glaucoma development in ocular hypertensive patients.

Researchers in Hong Kong measured the ratios in 140 eyes of 75 individuals. The team then used the measurements obtained with stereophotography, OCT and HRT to calculate the estimated five-year risk. Two glaucoma specialists evaluated the optic disc stereophotos (SP1 and SP2). 

The c/d values measured by OCT, HRT, SP1 and SP2 and their respective five-year risk of glaucoma development are as follows:

MetricC/D RatioGlaucoma

The maximum difference of cup-to-disc-ratio measurement was 0.64, while the maximum difference of the corresponding five-year risk was 24.02%.

The study noted that the estimated risks calculated by different methods of vertical cup-to-disc ratio measurement are not interchangeable and could affect treatment decision. Researchers called for refining the currently available risk estimation model for patients with ocular hypertension, as well as a deeper investigation of possibly integrating other parameters to the model, such as those measured by HD-OCT. The team concluded that unnecessary treatment for low-risk ocular hypertensive individuals would expose the patients to undesirable medication side effects without beneficial gain. Therefore, the reliability of this risk estimation is important.

Chan PP, Chiu V, Wong MO. Variability of vertical cup to disc ratio measurement and the effects of glaucoma 5-year risk estimation in untreated ocular hypertensive eyes. Br J Ophthalmol. August 29, 2018. [Epub ahead of print].