Updating the Glaucoma Diagnostic Tool Chest

Optometrists have new tools at their disposal to identify the presence and progression of glaucoma, even in patients who do not demonstrate visual field loss.

By Murray Fingeret, OD

The importance of accurately monitoring intraocular pressure (IOP) in glaucoma patients cannot be understated. Optometrists face the substantial challenge of forming a diagnosis and monitoring patients over time based on IOP measurements taken at a few moments in time during a few visits each year. But IOP is variable, and many factors influence it, including the time of day it is measured and the patient’s history of disease control.

TO THE POINT

Advances in technology now allow self-tonometry and measurement of RNFL thickness and parapapillary atrophy on OCT to be used as indicators of glaucoma status.

Several new technologies may help optometrists to accurately measure this important glaucoma risk factor. New devices such as self-tonometers, and new measurements on existing devices such as optical coherence tomography (OCT), may provide reliable data that optometrists can use to diagnose and follow glaucoma with greater certainty.

CONTINUOUS IOP MONITORING

Diurnal or circadian fluctuations in IOP occur in both healthy and glaucomatous eyes. In recent years there has been increased interest in the ability to monitor IOP continuously. Although technologies for 24-hour IOP measurements have been approved by the US Food and Drug Administration (FDA), such as the Triggerfish contact lens system (Sensimed), these devices are not yet available for sale in the United States. Now, optometrists have a way to assess a patient’s IOP profile throughout the day, rather than just at his or her appointment. Recent approval by the FDA of a self-tonometer (Icare Home, Icare) allows patients to measure and track their own IOP at various time points during waking hours, providing optometrists with a more thorough data set upon which to base management decisions.

Watch it Now

EyetubeOD Meeting Coverage: Emerging Technologies in Glaucoma Diagnosis
Murray Fingeret, OD, joins EyetubeOD Meeting Coverage from Vision Expo East in New York City to discuss updates to optometry’s toolbox for detecting glaucoma.

RNFL Measurement

OCT is a noninvasive imaging modality that provides high-resolution, cross-sectional images of the optic nerve, retinal nerve fiber layer (RNFL), and macula region. Its use for RNFL measurement in following glaucoma patients is well established, and it can also assist in glaucoma diagnosis. Spectral-domain OCT, which is an improvement from earlier time-domain OCT, is the platform used by most eye care providers today. A new version in development called swept-source OCT may be embraced in coming years.

In a recent paper, Schuman et al noted that visual field loss is not usually apparent until the RNFL average thins to approximately 75 μm.1 Thus, a large population of patients in relatively early stages of glaucoma with RNFL damage on OCT will have visual fields that are full.

Figure. The PPA image taken with the Spectralis OCT (Heidelberg) will allow evaluation of parapapillary atrophy. Here, a patient shows evidence of PPA, as seen in the blue area.

PARAPAPILLARY ATROPHY

Parapapillary atrophy (PPA) has been thought to be a sign of glaucomatous damage and has even been suspected of changing as glaucomatous damage worsens. The only tool we have had to monitor PPA change is retinal photography. Doctors evaluate retinal photographs over time, and this process is affected by subjectivity. Heidelberg Engineering, which manufactures the Spectralis OCT, is developing software that will measure PPA similar to how we measure the neuroretinal rim tissue. (Figure). By tracking these measurements over time, we may obtain a better idea of how reliable this region is for monitoring change. PPA has the potential to become another marker optometrists can monitor to develop a deeper understanding of glaucoma progression.

Change is the only constant in medicine. There has been an evolution in the diagnosis and management of glaucoma. New technologies—and even new findings using older technologies—have shown much promise. The introduction and clinical application of these tools will be exciting as optometrists continue to improve their ability to assess and manage glaucoma patients.

1. Schuman JS, Wollstein G, Kagemann L, et al. Retinal nerve fiber layer and visual function loss in glaucoma: the tipping point. Br J Ophthalmol. 2013;97(8):1088.

Murray Fingeret, OD, FAAO
• chief, optometry section, Brooklyn/St. Albans Campus, Department of Veterans Affairs New York Harbor Health Care System; clinical professor, State University of New York, College of Optometry; both in New York City
• financial disclosure: consultant, Carl Zeiss Meditec, Heidelberg Engineering, Topcon
murrayf@optonline.net