CONTINUING EDUCATION

Diagnosing a Deceptive Presentation

A patient with a history of surgery for a brain tumor presents with signs of glaucoma that defy classification.

By G. Richard Bennett, MS, OD, FAAO

I've been working exclusively in glaucoma patient care at the Eye Institute of the Pennsylvania College of Optometry at Salus University in Philadelphia for nearly 30 years. In this continuing education activity, I'll discuss three unusual cases that demonstrate the value of accurate diagnoses, appropriate treatment with new medications and ongoing patient education and follow up. I'll show how to effectively address emerging ocular surface issues that have become important in glaucoma treatment while focusing on reducing the threat of vision loss.

Glaucoma or Tumor?

In this case involving a 63-year-old Caucasian woman, who presented with blurred vision and floaters, nothing was as it seemed. Five years earlier, the patient had a surgically repaired pituitary adenoma. She faithfully had followed up with her neurosurgeon and neurologist, but not with her previous eye doctor. She had no known allergies and her only systemic issue was hypertension, which was controlled at 110/70 with atenolol.

Here are the additional findings of my exam:

■ Decreased visual acuity at distance (20/30 OD and 20/40 OS) and floaters OD for the past 4 months

■ Manifest refraction: OD +0.75-1.25×123 20/20-2; OS +1.50-1.50×087 20/20-1

■ Pupils: PERRLA, absent relative afferent pupillary defect (-RAPD)

■ Extraocular muscles: smooth and full

■ Confrontation fields: full OU

■ Color vision: within normal limits using AO pseudoisochromatic plates

■ Exophthalmometry: 18mm-18mm/107

■ Slit lamp examination: cornea, clear OU; anterior chamber, D&Q; lens, 2+ NS; vitreous, posterior vitreous detachment (PVD) OD

■ Gonioscopy: D-40-R with 1+ trabecular pigment OU

■ Intraocular Pressure (IOP): 10 mmHg OD, 11 mmHg OS.

Both optic nerves showed large cup-to-disc ratios of 0.75 with thinning of the inferior neuroretinal rims OD and OS with 90D lens evaluation (Figure 1). The peripheral retina was within normal limits, with no breaks or tears. The macula was normal. Threshold visual fields showed a suspicious superior nasal depression with a positive glaucoma hemifield test, suggesting the beginning of a nasal step in the right eye. The left visual field was normal and reliable. Heidelberg Retinal Tomography II (HRT II) showed a borderline Moorfields regression classification. The left eye was unreliable.

Figure 1. In this patient, both optic nerves showed large cup-to-disc ratios of 0.75 with thinning of the inferior neuroretinal rims OD and OS with 90D lens evaluation.

Alarming Fields

As you can see, except for the very large cup-to-disc ratio and thinning of the neuroretinal rims OU and the PVD in the right eye, my findings didn't indicate treatment at this time. I explained to the patient the ramifications of a possible descending optic neuropathy from the pituitary adenoma surgery. I wasn't concerned about her IOPs of 10 mmHg OD and 11 mmHg OS. However, I asked her to return in 4 months and urged her to continue seeing her neurologist and neurosurgeon.

As it turned out, the patient didn't come back for 3 years. When she returned, pupillary testing remained normal. The slit lamp examination was normal, with the exception of some early nuclear cataracts. Her IOPs at 14 mmHg OD and 12 mmHg OS remained low. Her fundus remained unchanged.

However, her threshold visual fields were alarming, even though they didn't reflect the appearance of her optic nerves. Profound loss of the visual field with total ablation of the superior hemifield was present OU (Figure 2). False negatives were very high in both of these fields, potentially indicating an unreliable field. You may have difficulty with patients not responding quickly enough, either because of arthritis or some other problem. So you need to be cautious about any single visual field that hasn't been repeated.

Figure 2. This patient's visual field shows profound loss with total ablation of the superior hemifield OU.

I referred the patient to her neurologist and asked her to come back for repeat visual fields in 2 months. Because of her low IOPs, glaucoma didn't seem likely. Even if I assumed she had low-tension glaucoma, such a profound progression in field loss wouldn't be likely over a 3-year period. I wanted to make sure she didn't have additional neurological issues contributing to the apparent visual field loss.¹

Late Again

Despite my request, she didn't return for the visual field test until 6 months later, when I discovered her IOPs had increased to 20 mmHg OD and 21 mmHg OS (morning measurements). This case predated the release of the Ocular Hypertension Treatment Study (OHTS), which showed that patients with thin central corneal thickness (CCT) and elevated IOPs were at higher risk for developing open-angle glaucoma.^2,3 There was no evidence that her IOPs were ever elevated beyond normal levels, but certainly the rise in pressure to a high normal level was disturbing given her very suspicious cupping.

During this visit, her visual field looked much better (Figure 3). However, the right eye still showed a marked superior nasal step, but it had improved from previous visual fields performed 6 months earlier. The left eye showed more of a generalized reduction of sensitivity but no focal loss, which was an improvement from the previous visual field. I repeated the IOPs in the evening and found no substantial difference from her morning pressures.

Figure 3. Visual fields from a 6-month follow-up visit showed improvement, although the right eye still demonstrated a marked superior nasal step.

Treating IOP

At this point, I believed there was sufficient evidence to diagnose the patient with open-angle glaucoma (likely normotensive) and begin treatment. I prescribed travoprost with sofZia (Travatan Z, Alcon), qhs OU. I called the neurologist and recommended a repeat MRI and neurological evaluation.^4,5

The neurology work-up remained negative. In addition, I ordered a cardiology evaluation, blood work and a carotid Doppler to rule out other potential contributing disease. Three months later, the patient returned to my office with IOPs of 10 mmHg OD and 11 mmHg OS, having reached her target IOPs in the low teens or lower. I continue to follow her closely and ask her to visit her neurologist regularly. At this point, CCT, which was tested in 2003, was normal.

I concluded this patient likely has normotensive glaucoma, although missed IOP spikes are certainly possible. Normotensive glaucoma is a diagnosis of exclusion, and this case is challenging. I continue to be cautious about the potential for contributing disease, while maintaining low target IOPs and a tight follow-up schedule. OM