GLAUCOMA DIAGNOSIS
OCT Applications in Glaucoma
Using various sources of information is the key to diagnosing and managing glaucoma more effectively.
By Terri Pickering, M.D.
Unfortunately, there's no single test you can administer to diagnose glaucoma. Nor is there any positive or negative result on which you can depend completely to draw definitive conclusions. As a result, glaucoma specialists have become experts at integrating various sources of information and relying on as much data as they can acquire on structure and function.
Elevated IOP used to be the key to diagnosing glaucoma, but of course that has changed dramatically in recent years. We know that certain individuals with slightly high IOPs don't have glaucoma while others with no IOP elevation, do. Central corneal thickness is also a risk factor. But now our primary focus is on changes to the retinal nerve fiber layer (RNFL).1 The cup-to-disc ratio and/or the RNFL thickness may change gradually over time, and both of these changes typically occur before we see any change in the visual field.
Therefore, RNFL analysis is a helpful, objective test that detects the earliest signs of glaucoma as well as progression. RNFL analysis includes scanning laser polarimetry, retinal thickness analysis, confocal scanning laser ophthalmoscopy and OCT — all of which are used in an adjunctive capacity to give us a full picture of the patient's status. In my practice, OCT is an important diagnostic tool, often helping me reach a conclusion when other tests are inconclusive.
This article will discuss the applications of OCT in glaucoma diagnosis and management.
Making the Diagnosis
Because RNFL changes are the key indicators of glaucoma, we use a variety of tests to get the overall picture. As I mentioned, OCT is an adjunctive diagnostic test so you don't absolutely need it as long as you have good images of the optic nerve that you can follow over time.
OCT offers its greatest value when identifying the classic glaucoma suspect. If a patient is referred to me with a suspicious optic nerve or an elevated IOP, but the visual field is normal, OCT can help me diagnose subtle abnormalities that occur in the optic nerve rim thickness. The device also has been shown to detect glaucomatous change in the RNFL before any signs appear in standard automated perimetry.2 And detecting preperimetric glaucoma is key to preventing RNFL loss and preserving visual acuity, particularly in younger patients.
| Using OCT to Verify Early Glaucoma A healthy, 39-year-old Caucasian man was referred for evaluation for pigment dispersion. The patient had a moderately elevated cup-to-disc ratio of 0.5 to 0.6, as per his optometrist. His IOP was 13 mm Hg OD and 14 mm Hg OS. This patient was a glaucoma suspect, so I wanted to get good baseline data. His visual field and central corneal thickness tests were normal, but his OCT scan was abnormal. To verify the OCT, I carefully examined his optic nerves and found that his cup-to-disc ratio was 0.85 × 0.85 OD and 0.85 × 0.80 OS. Both nerves were very thin temporally. Despite the patient's low IOP and normal visual fields, I diagnosed him with preperimetric pigment dispersion glaucoma. I explained to him that we needed to start glaucoma treatment as a preventive measure to preserve his vision. At just 39 years of age, he was surprised by the diagnosis. OCT helped me to visually demonstrate his diagnosis and explain the importance of early treatment in preventing vision loss from his disease. |
In addition, OCT is an excellent alternative for patients who have trouble taking the visual field test. If patients have low vision, for instance, structural examination can be our only guide in detecting glaucoma.
Glaucoma Management
As you track glaucomatous progression throughout treatment, OCT offers comparative analysis against baseline scans. It also provides a normative database, which gives you age-matched data comparisons. Using all of the device's capabilities, you can determine when a patient in the normal range becomes borderline, how one eye compares to the other and when asymmetry develops.
We can more easily detect when undiagnosed patients go from glaucoma suspect to the beginning stages of glaucoma. And we can keep track of how therapy is controlling the disease and make adjustments as needed to prevent progression.
Investing in OCT
When you begin practicing ophthalmology, I suggest you inquire about OCT technology for glaucoma detection and other applications. OCT gives you objective data and analysis in a device that's easy to use and maintain, and its visual display can help with patient education and compliance. The device's sensitivity and objectivity are helpful in detecting and following glaucoma as well as other ocular diseases. nMD
| Terri Pickering, M.D., is a glaucoma specialist who practices general ophthalmology and performs cataract surgery at the Glaucoma Center of San Francisco. |
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