How I Examine for Glaucoma

A multi-faceted approach to accurate diagnosis.

BY ANDREW RABINOWITZ, MD

In recent years, the tests and instruments available to ophthalmologists in examining for glaucoma have been rapidly expanding. Today, a thorough examination of a patient can involve more than a half-dozen different tests, ranging from traditional visual fields, fundus photography and slit-lamp biomicroscopy to the latest SD-OCT imaging — all of which are capable of providing clinicians with helpful clues to be weighed and evaluated. Add to those measurable tests some basic observations of the patient's physical state and you have a wealth of information with which to make an accurate diagnosis.

But interpreting and balancing the results of many tests and observations to arrive at a diagnosis is still more of an art than a science.

Here, I will describe the elements of what I believe constitutes a thorough glaucoma examination — how to proceed, what we should be looking for and what findings weigh most heavily on the diagnosis and in developing a treatment plan if one is necessary. I will conclude the article with a brief comment regarding the critical element of any treatment plan — achieving patient compliance.

In evaluating a patient for the presence of glaucoma, or for the occurrence of progressive glaucomatous changes, the work-up should include a series of questions as well as the collection of a core set of data points.

First Step: A Complete History

Obtaining a thorough general medical history is vital.

Attention to any history of trauma of surgical or other etiology, such as a motor vehicle accident, is important. Any incident that prompted the need for blood transfusions is of pertinence. This is because a trauma that required transfusion was likely marked by significant blood loss and at least transient hypovolemia. This hypovolemia can cause unilateral or bilateral optic nerve hypoperfusion and subsequent ischemia.

I have seen many patients referred to my practice over the years for possible low-tension glaucoma. A thorough medical history has revealed the type of trauma outlined above and caused the patient to have bilateral optic atrophy, which had many characteristics seen in glaucomatous optic atrophy. It is also critical to review the patient's current systemic medications. The use of oral beta-blockers, either historically or currently, can represent an exacerbating factor in the promotion of low-tension glaucoma. Oral beta-blockers can — in certain “at risk” patients — decrease heart rate and blood pressure and worsen an underlying low-tension glaucoma. Removal of the oral beta-blocker, if blessed by the prescribing internist or cardiologist, can help enhance optic nerve perfusion and lessen the impact of low-tension glaucoma. Failure to remove the oral beta-blocker in an “at risk” patient can mitigate the benefit of aggressive intraocular pressure reduction.

Once the pertinent medical and ocular histories are obtained, as well as a comprehensive review of the patient's present medications is completed, a thorough family history of ocular diseases is required. A family history of blindness from glaucoma is a significant risk factor in a patient with glaucoma or glaucoma suspicion.

Just before I start the ocular exam I look at the patients general habitus. If the patient is morbidly obese, I assess the girth of the neck. A thick neck can lead to elevated episcleral venous pressure and elevated intraocular pressure. In these cases, significant weight loss can possibly improve their intraocular pressure by decompressing the venous passages in the neck and upper mediastinum. Patients with this habitus can also suffer from sleep apnea. Untreated apnea can lead to optic nerve ischemia and worsen an underlying glaucoma. Continuous positive airway pressure (CPAP) can improve oxygenation to the disc and brain.

If the patient is frail and cachectic I will carefully evaluate for carotid artery bruits. Any bruit can suggest the risk of ipsilateral or contralateral ischemia at the level of the ophthalmic artery and can contribute to disc ischemia.

Thus, even before any ocular examination is initiated, a comprehensive history and overall physical assessment is a necessary step in the glaucoma work-up.

Visual Fields and Examination

Following the history, the visual acuities, as well as the present distance and near corrections, should be recorded. Once these are obtained, the patient can perform Humphrey Visual Field Testing. I use the 24-2 program with a stimulus size 3 with a threshold program. Once the visual field is completed, we move onto the examination.

On the patients initial exam, a pupillary examination looking for even a subtle afferent pupillary defect should be performed. Next, a complete evaluation of the facial and external ocular structures — including eyelids — is in order. Once attention is turned to the slit-lamp exam, the intraocular pressures should be measured prior to gonioscopy and prior to dilation. The time of day should be recorded, along with the method by which the pressure was checked, should also be noted.

I take great care to note any asymmetry in the IOP Corneal pachymetry is then performed to obtain baseline corneal thickness. Thin corneas are an important indicator of increased risk for glaucoma. Dynamic gonioscopy with a four-mirrored lens should then be performed to obtain an understanding of angle anatomy. Some general ophthalmologists are not doing gonioscopy because they find it a difficult test to perform, but I believe gonioscopy is the key to viewing the trabecular meshwork and should be a part of any thorough glaucoma investigation.

The pupils are then pharmacologically dilated, provided they are not occludable based upon their gonioscopic status. I then perform a stereobiomicroscopic exam of the optic nerve heads with a 78-D or 90-D lens at the slit lamp. I also evaluate the macular area at this time. Finally, a peripheral retinal exam is performed with a 20 D lens and an indirect ophthalmoscope.

The Importance of Asymmetry

As I review the findings, I attempt to look for any consistent asymmetry in all the data, including intraocular pressure, optic nerve head status and visual field performance. The presence of asymmetry raises my index of suspicion for glaucoma.

In my experience, glaucoma rarely presents in a symmetric fashion. The degree of asymmetry can vary, but even in the earliest of cases, some degree of asymmetry can be appreciated. This is often contrary to ocular hypertensives, who frequently reveal symmetric intraocular pressures.

Following completion of the exam, I will obtain dilated stereo-disc photos for future reference. I will then ask the patient to return for follow-up testing and IOP measurement in the next one to four months.

Continued Follow-Up

If I place a patient on a medication, I will ask them to return in a month to repeat the intraocular pressure check and ancillary testing. I often request that the patient return at a different point in the diurnal cycle for the second visit. At the time of that exam, I will often also have them perform either baseline blue-yellow perimetry (short-wavelength automated perimetry: SWAP) or frequency-doubling perimetry: FDT). Note: some patients have difficulty in completing a SWAP test as they find it highly stressful. Additionally, I will perform a baseline OCT scan of the nerve fiber layer.

Subsequent to these tests, I will repeat my slit-lamp exam and repeat the IOP measurement. If I had any concerns about the patients gonioscopic findings on my initial exam, I will perform repeat gonioscopy at this time to confirm my suspicions or impressions.

If the patient's pressures are controlled, I will then request follow up in two to four months. If the intraocular pressure is not controlled, I will ask the patient to return in a month, especially if a change is being made to the treatment plan.

Subsequent visits are then arranged at one- to six-month intervals, depending upon the unique aspects of each case. I find that more frequent visits provide reinforcement to encourage compliance with the patient's treatment plan.

Depending upon the degree of suspicion and/or pathology, I will then determine if repeat visual field testing is warranted inside of the first year of care. For patients with significant defects and elevated intraocular pressures upon presentation, I will often repeat perimetry once their pressures are brought to their target level.

For patients with no visual field defects upon presentation, I might not repeat visual field testing until one year. For patients with low-tension glaucoma, I will always examine the disc to check for Drance hemorrhages. If a hemorrhage is present, I will obtain photographic documentation, both upon identification as well as at time of resolution.

The use of OCT for both initial diagnosis and to monitor for progression appears to be evolving. Standards for the use of OCT as both a screening tool to search for pre-perimetric glaucomas (glaucoma without visual field loss) as well as a modality to monitor for the presence of progression are also rapidly evolving.

Overall, I strongly believe that examining for glaucoma in this manner provides me with the best opportunity to correctly evaluate the patient. It also allows me to develop the most appropriate treatment plan when treatment is deemed necessary.

A Word About Compliance

In treating glaucoma patients, we as practitioners frequently encounter one huge obstacle that we should make every effort to overcome. It is the issue of compliance. We can perform the most thorough and professional initial examination and follow-up possible, but it is all for naught if the patient does not comply with the treatment plan.

One of my goals during the examination is to explain to the patient the purpose of the tests being performed and how these tests can help “us” in devising a treatment plan that will control the effects of the disease. I try to make it as clear as possible that the patient and I are “partners” in making the treatment plan work.

One idea that I have considered recently is to provide each patient with a folder that contains all of the patient's test results, including the relevant images. Would this impress upon each patient the seriousness of glaucoma and the importance of strict compliance with the treatment plan? It is something to consider.

And it almost goes without saying that better ways to administer glaucoma medications in some sort of sustained-release format would go a long way toward eliminating the compliance problem. Given the recent progress made in this area by Richard Lewis, MD (medication-filled punctal plugs) and others, this is a wish that could become an everyday reality in the next few years. OM

Andrew Rabinowitz, MD, is a glaucoma specialist at Barnet Dulaney Perkins Eye Centers, a multi-location practice based in Phoenix. He can be reached via e-mail at andrewrabinowitz@aol.com. He has no financial interest in any product mentioned in connection with this article.