Glaucoma Grand Rounds

Never Yield On One Field

J. James Thimons, O.D.

A local doctor referred a 77-year-old white female to our practice for a consult on her poorly controlled glaucoma. She was in no acute distress, with little contributing medical history. She had a family history of glaucoma on her mother’s side and cataracts in both parents’ families. She was taking Betoptic S (betaxolol suspension) 1 drop bid O.U. She was taking no other medication and had no known drug allergies. Except for a gall bladder resection 30 years earlier, she had no history of surgery.

Physical Examination

Corrected visual acuity was 20/15- in each eye. Refraction revealed mild myopia with astigmatism. External evaluation showed the adnexa was clear and symmetric. Pupillary reactions were 3/3, 2+3, -MG. Extraocular muscle movements were normal. Applanation tensions were 19mm Hg O.D. and 20mm Hg O.S. at 10 a.m.

The slit lamp exam showed clear corneas with deep anterior chambers. The iris, lens and anterior vitreous compartment were unremarkable. Gonioscopy revealed ciliary body 360° O.U. with 1+ to trace pigmentation. There was no evidence of angle abnormality.

Dilated fundus exam showed cup-to-disc ratio to be 0.8-0.85 vertically O.U., with a slightly lesser horizontal assessment at 0.7-0.75. The inferior temporal aspect of each disc showed thinning with concurrent wedge defects of the nerve fiber layer bilaterally in the corresponding anatomical region.

Visual field testing showed superior arcuate bundle and nasal sensitivity decreases with some early changes in the inferior arcuate zone.

Discussion

Management of this case hinges on the visual field assessment and subsequent review of optic nerve function as well as IOP. To lower her pressure further, I added Xalatan (latanoprost) qd to her therapy.

Results from the 1-month follow-up visit complicated our management. While Xalatan helped lower her IOP to 15mm O.D. and 14mm O.S., she showed what appeared to be progressive visual field change. A repeat examination confirmed this.

One of two causes seemed likely. Either the progressive visual field change took place secondary to nerve damage that occurred before I lowered her IOP further, or her optic nerve status was still compromised, even at the lowered pressure.

After we discussed the potential for adding a third drug or using a laser, she took a repeat visual field as a baseline prior to laser therapy. This field demonstrated significant improvement in sensitivity and was consistent with the performance of her visual field and initial referral 7 months earlier. Although this patient showed apparent progressive visual field changes in that time, the optic nerve, IOPs and nerve fiber layer did not vary.

This patient’s performance brings up an important, and not infrequent, aspect of glaucoma care: the reliability of visual field assessments. One of your greatest concerns is interpreting visual field information to determine if the patient is undergoing progressive change over time, and not simply exhibiting variability that would demonstrate non-progressive status when plotted over multiple tests. Patients often show mild to moderate variability in the normal assessment of visual field function. Rarely will these patients show progressive change over time that you can plot.

When this individual did show apparent progression of visual field loss over a 6-month period, it prompted the co-managing glaucoma specialist to discuss laser intervention to further lower IOP. However, that conclusion had two inconsistencies: The IOP had already been lowered, and the optic nerve and nerve fiber layer were unchanged from initial evaluation.

Although there are several optic nerve changes that are impossible for a clinician to identify, the types of changes necessary to produce progressive visual field loss of this type would have been noticeable. So, the optic nerve changes should have been consistent with the visual field changes. The fact that they weren’t, along with stable findings in other areas, prompted me to reinvestigate the visual field.

A good rule: Never make a decision that puts the patient at risk or is irreversible based on a single visual field.

Also, patients may give better feedback on field exams at different times of the day. I base this on what they tell me about when they perform the best. When patients consistently perform poorly, I schedule them at the time of day they have the most energy and focus. This is a great way to improve their ability to perform visual fields.

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