CLINICAL CHALLENGES
Pieces of a Puzzle
Gathering evidence is key to a correct diagnosis of pigmentary glaucoma.

The renowned neuro-optometrist Dr. Larry Gray often describes diagnosing eye disease as being like a detective who's looking for clues. Another way of looking at this is like putting together a jigsaw puzzle. You must find all the pieces and then make sure they fit. This case challenged me to do just that.

Meet Mr. Harvey

Mr. Harvey was a 74-year-old self-described "gentleman farmer" whose passion was riding a tractor. He took atorvastatin calcium (Lipitor) for high cholesterol, loratadine with pseudoephedrine (Claritin D) for chronic allergies and an aspirin a day for cardiac health.

Four and five months earlier, my cataract surgeon had removed cataracts from both of Mr. Harvey's eyes. Both procedures went well and left him with visual acuities (VAs) of 20/30-2 OD and 20/25-3 OS. He seemed satisfied with this vision, although I expected better VAs.

Mr. Harvey was initially referred to me as a glaucoma suspect. I agreed with this suspicion based on my clinical findings, which was why he was in my office again, months after his cataract extractions. I wanted to take another look at his optic nerve head (ONH) and perform further tests to assess whether he indeed had glaucoma. Mr. Harvey had no other ocular com plaints.

The details

Mr. Harvey's VA remained at 20/30-2 OD and 20/25-3 OS. A refraction of -0.75 -0.75 x 095 OD and -1.00 -1.00 x 085 OS didn't change the vision in either eye. His pupils were 5 mm and round OU but were sluggishly reactive with no afferent pupillary defect.

Extraocular muscles showed no restriction, and confrontation fields were full OU. The slit lamp revealed irregularities of the iris sphincter muscle at the papillary margin. In addition, iris atrophy was present throughout the iris stroma OU. I also noted a few small areas of iris transillumination (see photo, next page).

Posterior chamber intraocular lenses (IOLs) were well posi tioned OU, and there was no opacification of the posterior capsules. I saw a faint dusting of pigment from the iris on the posterior surface of the corneal endothelium, although this wasn't noted pre-operatively. I mea sured the intraocular pressure (IOP) as 17 mm Hg OD and 19 mm Hg OS.

Before dilating Mr. Harvey's pupils, I placed a Sussman 4 mirror gonioscopy lens on his eyes. I graded his angles as Grade 3 to 4 in all quadrants OU. More importantly, the trabecular meshwork in each eye was heavily pigmented, and I found two large peripheral anterior synech iae in the nasal quadrant OS.

Disk data

Mr. Harvey's ONH appearance further increased my suspicion of glaucoma. I estimated his cup-to-disk ratio (C/D) at .7/.7 OD. The neuroretinal rim was symmetrical inferior to superior and temporal to nasal. The lamina cribrosa was visible, but I saw no notches or baring of the circumlinear vessel. The disk in this eye was large and had a steep slope.

His C/D OS was .7/.75 with a focal notch at 7 o'clock. I saw lamina but no baring of vessels. Again, the ONH was quite large, with a steep slope to the cup.

Given the large C/D, the focal notch and the visible undermining of the neuroretinal rim, I believed that Mr. Harvey had glaucoma. The appearance of his irises along with the pigmented trabecular meshwork pointed to pigmentary glaucoma (even though no Krukenberg's spindle was present).

I wanted to obtain a more objective view of the ONH and macular region, so I performed an analysis using a Retinal Thickness Analyzer (RTA).

Notice lightening iris color toward the periphery and near translucence at pupillary margin.

The RTA

The RTA is a new technology manufactured by Talia Technology, Ltd., that allows us to see both the ONH and macular region in a unique fashion.

The instrument uses a scanning laser to produce optical cross sections of the ONH and peripapillary region, the posterior pole or both. At each point scanned, the technology produces 16 cross sections that show, in real-time images, the thickness (or thinness) of the tissue at that point. A macular scan consists of five different 6 mm by 6 mm areas.

An optic disk scan includes the entire disk and the temporal and nasal retina adjacent to the ONH, including the papillomacular bundle. The individual optic sections are combined in the analysis to derive a thickness map for the area and a 3-D topography map.

The glaucoma scan further analyzes the thickness of the nerve fiber layer at all four quadrants and produces a stereometric analysis of 12 parameters of the ONH that's compared to normals. The macular scan derives thickness deviation and probability plots relative to normals and analyzes the data in eight parameters.

The data give both global and quadratic measures, which allow for an even more precise view of the ONH and nerve fiber layer.

The data that the RTA provides are extremely helpful in following patients with known glaucoma or diabetic macular edema. It's equally important in helping us make the initial diagnosis.

Mr. Harvey and the RTA

In Mr. Harvey's case, I assumed that the RTA would confirm some nerve fiber layer attenuation or other anatomic irregularity consistent with glaucoma. The analysis did show mild nerve fiber thinning at the superior and nasal quadrants OS (consistent with the focal notch seen clinically), but other than that the disk scan was relatively normal. The scan OD was essentially normal too, except that the mean retinal nerve fiber layer thickness was significantly thinner than normal. This was consistent with a global type of nerve fiber layer loss.

The macular scan, however, was a shocker. The instrument revealed abnormal macular thickening and elevation OD>OS. I will deal further with this unexpected finding in next month's column.

One final puzzle piece

One year earlier, Mr. Harvey had undergone a visual field test that was normal OD but showed a slight arcuate scotoma superiorly OS. I repeated the test, which confirmed these findings. The visual field OD showed no focal or pattern type defects, but the mean sensitivity was slightly diminished. The OS depicted a mild superior arcuate scotoma. I now had all of my puzzle pieces. But did they fit?

Clearly Mr. Harvey had glaucoma, OS > OD, based on the RTA data and the ONH appearance. The IOP was never in the abnormal range; thus he didn't have primary open angle glaucoma. He had characteristics of pigmentary glaucoma, but he didn't fit the demographic bill for this disease (see "Clinical Pearls," below). Ruling pigmentary glaucoma out left me with normal tension glaucoma as a diagnosis. Pseudophakic pigmentary glaucoma was also a distinct possibility.

If the shoe fits . . .

This condition certainly wasn't acute, and Mr. Harvey had shown signs of it before surgery, so I ruled out pseudophakic induced glaucoma.

Despite Mr. Harvey's age, I diagnosed pigmentary glaucoma and began treating him with brimonidine tartrate (Alphagan) OU b.i.d. After 2 months of treatment his IOP remained essentially the same, so I switched him to timolol hemihydrate (Betimol) OU b.i.d.

Now, 8 months after this diagnosis and treatment began, Mr. Harvey's IOP hovers consistently around 13 mm Hg OU. He's tolerating the drops well and so far I've seen no progression in any of his parameters. Now, about his macula . . . 

Contributing Editor Eric Schmidt, O.D., is director of the Bladen Eye Center in Elizabethtown, N.C. E-mail him at KENZIEKATE@aol.com.