Latest Developments in OCT Enhance Its Role in Glaucoma Care

Spectral-domain technology and progression detection algorithms increase confidence in treatment decisions.

By Desiree´ Ifft, Contributing Editor

Now that spectral-domain OCT (SD-OCT) has made its way into nearly every glaucoma practice, doctors and patients are benefitting from its advanced capabilities. Its faster image acquisition speed improves resolution, reproducibility and repeatability, enabling new strategies for achieving the ultimate goal in glaucoma care: objective detection of disease progression. “Determining whether a patient is getting worse or not getting worse is our holy grail,” says Robert J. Noecker, MD, a glaucoma specialist with Ophthalmic Consultants of Connecticut. “Today’s OCT instruments give us more confidence in what we’re seeing from scan to scan.”

The basis for how Dr. Noecker employs OCT in his practice includes the following.

■ Treatment decisions must rely on all available testing modalities. As advanced as OCT has become, it doesn’t replace the other diagnostic information that can — and should — be obtained.¹ Also, a comprehensive baseline exam for the glaucoma patient is crucial. Dr. Noecker’s baseline exam consists of OCT of the retinal nerve fiber layer (RNFL) and optic disc; visual field test, usually with the Humphrey 24-2 SITA software; pachymetry; IOP measurement; examination of the angle and optic nerve; and, often, anterior segment OCT to further assess whether the angle is narrow or open. He also obtains a baseline macular OCT.

Dr. Noecker adds, “When steps are taken to lower IOP, perhaps by adding a fixed-combination medication to the patient’s regimen or performing surgery, all initial testing should be repeated in order to reset the baseline.”

■ OCT is most useful in early or suspected glaucoma. “Studies show that changes in RNFL thickness often precede changes in the optic nerve or visual field changes,² so that’s where OCT carries more weight in relation to other findings,” Dr. Noecker says. “We also know that SD-OCT is an improvement over time-domain OCT for detecting early-stage glaucoma.”³ Once RNFL thickness declines to a certain point, it’s thought that visual field testing is a more reliable way to assess disease state.

■ Frequency of OCT testing depends on the level of confidence that glaucoma is or isn’t progressing. “When IOP is in the targeted range and OCT results are within the range of the normative database, I can be reasonably sure the patient is stable,” Dr. Noecker explains. “In that scenario, when all testing is correlating well, I perform OCT every 6 months. When tests don’t correlate, for example, OCT indicates RNFL thinning in an eye with presumed controlled IOP, (Figure 1) it’s likely that the patient is unstable, and I perform OCT more frequently to help me determine what’s happening.”

Figure 1. In this patient, whose visual field was normal, OCT scanning of the right RNFL showed thinning inferiorly.

How frequently he performs OCT in an unstable patient, which may be weekly or monthly, depends on how urgent the need is to use the disease progression software, which requires a certain number of test sessions, typically three, to provide an assessment. “The normative databases compare each patient to the average, but average is a big range and not everyone is average,” Dr. Noecker says. “The progression software allows us to use each patient as his or her own control. If the progression software shows changes (Figure 2), it’s an indication that the changes are real,⁴ which means treatment must be adjusted accordingly. Then the faster we can stabilize the patient, the faster we can return to testing with OCT every 6 months.”

Figure 2. Long-term imaging with OCT shows changes with progression analysis.
Images courtesy of Robert J. Noecker, MD, MBA

Dr. Noecker offers this tip: “If you want to start using the progression software right away, it’s effective to scan the patient three times in one visit, rather than waiting for separate visits.”

■ A macular OCT scan can provide useful information. “There is evidence that changes in the macula, particularly ganglion cell loss, can be just as sensitive for diagnosing and monitoring glaucoma as RNFL thinning,^5-7 especially in early glaucoma,” Dr. Noecker notes. “The ganglion cell complex can be measured reliably with SD-OCT, so that scan or at least a total macular thickness scan should be done for every glaucoma patient.”

Further Improvements Forthcoming

In addition to the retinal ganglion cell layer, the relationship of retinal hemodynamics to glaucoma is being further explored. For example, optic disc perfusion, as measured by Doppler or swept-source OCT angiography, may prove useful in detecting pre-perimetric glaucoma and change.⁸ Dr. Noecker says, much like currently available OCT devices, future improvements “will be indispensable tools for guiding our treatment choices, confirming they’re effective, and helping to alert us when a different or additional therapy is required to prevent disease progression.” ■

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