PPG: To treat or not to treat

Although the two glaucoma specialists presented opposing views - Dr Greenfield taking the affirmative position and Dr Singh presenting arguments against the need to diagnose and treat PPG - their discussions reflected the need for the decision to be individualized based on risk assessment and the importance of continued follow-up.

In deciding the approach to management of PPG, Dr Greenfield advocated applying the 'Principle of the 3 Rs' that considers: 1) eyes with PPG are probably at greater Risk for developing progressive visual field changes, 2) the need to measure the Rate of change, and 3) the need to Re-evaluate these eyes constantly for risk factors associated with progression.

"However, there is also a role for observation in eyes with minimal risk of loss in vision-related quality of life, a slow velocity of change, or patients with reduced life expectancy," Dr Greenfield added.

Evidence in favour of treatment

One of the limitations in guiding therapeutic decisions for PPG is that there are no randomized controlled trials that specifically enrolled patients with PPG. However, it can be assumed that a subset of patients in the Ocular Hypertension Treatment Study (OHTS) had undetected PPG, and in the Diagnostic Innovations in Glaucoma Study (DIGS), there was a subset of patients with baseline retinal nerve fibre layer (RNFL) atrophy. Data available from these cohorts indicate they have a greater risk of disease progression than their counterparts without evidence of structural abnormality, according to Dr Greenfield.

In DIGS, patients with suspected glaucoma with baseline RNFL atrophy had a four-fold increased risk of developing perimetric disease during follow-up, and those whose optic nerves showed glaucomatous progression over time had a 26-fold increased risk of developing visual field loss.

"Imaging plays a critical role for assessing the risk of visual field loss in eyes with PPG," Dr Greenfield said. "Development of a visual field defect can often be predicted by identifying eyes with an abnormally thin retinal nerve fiber layer thickness using either scanning laser polarimetry or time-domain OCT, according to findings from the DIGS study."

"Data from the Confocal Scanning Laser Ophthalmoscopy (CSLO) ancillary study of OHTS showed the risk for developing abnormal visual fields was increased nine-fold in eyes with abnormal baseline optic disc topography. Furthermore, in OHTS, two of the five originally described risk factors for converting to glaucoma, increased cup–disc ratio and visual field pattern standard deviation, are surrogates of PPG," he added.

Monitoring of patients with PPG

"Careful surveillance of patients for progression is important to identify those who are undergoing fast progression. Structural and functional data from at least five exams are needed to calculate the rate of progression. Frequent re-examination is important to assess the development of new risk factors, such as increased IOP or optic disc hemorrhage, that might alter the threshold for initiating therapy," Dr Greenfield said.

"Fundamentally, we need to individualize therapy based on life expectancy and risk assessment," he continued. "Data from a recently published analysis from the OHTS showed delayed treatment in eyes at the highest risk for developing change increased the cumulative incidence of developing visual field loss, the incidence of bilateral visual field loss, and hastened the onset of developing glaucoma by as much as 2.5 years."