BLOG: How often should I repeat gonio?

ByDoug Rett, OD, FAAO

Gonioscopy is a vital test to perform when suspicious of a glaucomatous process for your patient.

But for our glaucoma patients, once we’ve done it, how often should it be repeated?

Let’s assume a hypothetical patient is diagnosed with glaucoma and has very early field loss, open angles on gonio and normal pachymetry. My gut has always told me that for a patient like this, I’ll repeat gonio every 5 years or so.

An informal survey with optometrists I know found that most people would repeat the test “about every 5 years,” but they didn’t seem very confident with their answer. We should do better than gut feelings. I went to the literature to see if I could find an answer.

The American Academy of Ophthalmology’s Preferred Practice Patterns (PPP) suggest that gonio be performed at the baseline exam where glaucoma is suspected and then “periodically” after that, which they suggest is every 1 to 5 years. For closed angle cases, they recommend repeating gonio to “determine interval changes,” but leave the frequency up to the provider. One would assume that it would be at least as frequent as the open angle recommendations and more appropriate to be annual, especially if iridotomy is being considered or has already been performed. But for the purpose of this article, we’ll focus on open angle patients.

When determining reimbursement, Medicare acknowledges the PPP recommendations of every 1 to 5 years, and a review of the glaucoma literature finds this quote from McCune and Corcoran:

“Repeat testing is indicated when medically necessary for new symptoms, progressive disease, new findings, unreliable prior results or a change in the treatment plan. In general, additional testing is warranted when the information garnered from the eye examination is insufficient to assess the patient's disease adequately. In other words, if a patient has a history of glaucoma (or other indicated condition) and the ocular examination reveals an unstable or worsening condition, then more extensive testing may be justified. We would not expect a claim to be filed for a patient with stable visual fields who presents with no complaints or for someone with a controlled condition.”

Gonioscopy is vitally important to perform on patients in whom you suspect glaucoma. It should be part of our glaucoma checklist. When I perform it on a patient who has open angles on Van Herick, the main things I’m looking for are:

Is it potentially occludable? That is, does it need a laser peripheral iridotomy? This is an obvious reason to do gonio, but it needs to be emphasized. Subtle narrowing could be a reason why the IOP is creeping up and could be missed on Van Herick. As a mentor once told me, you can’t call it “open angle” until you look at the angle.

Check the amount of pigmentation. Secondary glaucomas like pigment dispersion glaucoma (PDG) and pseudoexfoliation (PXFG) will cause hyperpigmentation of the trabecular meshwork. This can be a subtle finding and only appreciated on gonio. It is especially important to do gonio bilaterally, as comparing the level of pigment of one eye to the other can be illuminating. I make it a point to write the level of pigment for each quadrant as well as the structures I see.

Something else to keep in mind to separate these two secondary glaucomas: in PDG, there should be pigment in the trabecular meshwork and Sampaolesi’s line, whereas PXFG will have pigment only in the trabecular meshwork.

Look for signs of recession. Recession can be hard to detect, especially if it’s 360 degrees. But most angle recession will have an area where the iris is running flat and then just bends posteriorly. That’s what I look for when assessing for recession. The astute clinician also knows that the scleral spur widens after recession, so compare the width of the spur between the two eyes.

Look for a mass or signs of neovascularization. Rare things, true, but if they are missed there would be devastating consequences.

I think a good practice pattern would be to do baseline gonio on all your patients for whom glaucoma is suspected, even if the risk is low. After that, repeat the test when a significant rise in IOP occurs or if any secondary glaucoma characteristics are identified or in 5 years, whichever comes first. And if the glaucoma is a secondary type, then the gonio should be closer to annually. I’d be curious to hear if anyone had a gonio claim rejected by an insurance company and for what reason. Send me an email. After this literature review, I think I have some gonio to do.

References:

Allingham RR, et al. Shields Textbook of Glaucoma. 6^th ed. Lippincott Williams & Wilkins, 2010.

American Academy of Ophthalmology Preferred Practice Patterns Glaucoma Panel. Primary Angle Closure. http://www.aaojournal.org/article/S0161-6420%2815%2901271-3/pdf.

McCune DM, et al. Glaucoma Today. September/October 2008.