CLINICAL CHALLENGES
A Diagnostic Dilemma
Was a cataract alone responsible for Jewel's poor vision?

We each have a routine for treating patients. That's how we can deliver the best care efficiently. But this routine can lead to complacency, even in the best of us. Fortunately, there's always a case or two each day that challenges us and makes us think hard about the diagnosis or what the best treatment is for that patient. This month's case illustrates one such diagnostic dilemma.

Meeting a Jewel of a belle

Jewel was the stereotypical southern belle. At age 62, her "Nawth Cawlina" accent was thicker than most and she seemed genuinely interested in whomever she spoke to.

She came to see me because she was having a "dreadful time" seeing with her right contact lens. The lens was still comfortable, but over the past two months, Jewel had noticed a change for the worse in her vision. When I asked specifically about the onset of the decreased vision, she noted that it was abrupt and hadn't really changed much since she first noticed it. She denied any trauma to the eye and said there was no discomfort, redness or discharge.

Jewel was in good health. She took only estrogens/medproxyprogesterone (Prempro) and alendronate (Fosamax) and had successfully worn contact lenses for more than 20 years.

A monovision technique served her well in her job as an assistant principal. Ten months previously, she had come to my office complaining of blurred vision OD. Her visual acuity (VA) at that visit was OD 20/25-2 and OS 20/20. I diagnosed a Grade 1 posterior subcapsular cataract (PSC) OD then, but neither of us felt that a cataract extraction was warranted at that point.

Now though, Jewel's vision was indeed worse. She also said that she was noticing halos around car lights at night and felt uncomfortable with night driving. Her VA measured 20/60-2 OD and 20/25 OS.

The VA didn't improve with a pinhole occluder. A refraction showed an increase of 0.75D myopia OD, but Jewel's vision was just 20/60 and "doubled." VA OS was 20/25+2 with an extra -0.50D. Her anterior segments were normal with the exception of a 1+ central PSC OD which, with the slit lamp, appeared somewhat more dense than before and a trace PSC OS. Her intraocular pressure measured 17 mm Hg OU.

A clear-cut cataract?

At this point, it would've been easy to say that an enlarging PSC caused Jewel's decreased VA OD. After all, the PSC did appear to be a bit larger and she had monocular diplopia through the phoropter, not to mention the shadows she saw while driving at night. Others could attribute all of these problems to a cataract, but to me, the PSC appeared only slightly larger than it was before. It certainly hadn't increased by 50%. I struggled to grade it as even a 2+ PSC. Was Jewel's cataract really large enough to cause 20/60 VA?

Obviously I needed to gather more information. It was possible that the cataract was the sole culprit, but before saying that, I needed to rule out other diseases. I needed to dilate Jewel's pupils, but first I had her look at an Amsler grid. She noted a slight metamorphopsia at fixation OD but no distortion OS. I dilated her pupils and looked closely at her retinas.

Muddying the waters

Consistent with her Amsler grid response, Jewel's macula was abnormal OD. Examination with a 78-D lens revealed a disorganized, wrinkled epiretinal membrane (ERM). The ERM was denser in some spots than others and was causing a focal disruption at the foveal avascular zone.

There was focal traction that gave the appearance of a macular hole. I projected a thin slit beam over the hole and it didn't bow posteriorly away from me. This negative Watzke-Allen phenomenon ruled out a macular hole. I didn't see any edema at the macula, but there certainly were focal areas of elevation caused by the ERM. Jewel's left retina was completely normal.

Before I could prescribe any treatment, I first needed to accurately diagnose Jewel's macular condition. She obviously had an ERM, but were there any other problems? I had already ruled out a macular hole based on the 78D appearance of her retina. Other possibilities included central serous choroidopathy (CSC), macular edema, sensory pigment epithelial detachment (PED), subretinal neovascular membrane (SRNVM) or a "pseudo-hole."

The other question I needed to answer was how much of the VA drop had been caused by the retinal loss and for how much of that was the PSC responsible?

Collecting the evidence

Many diagnostic tests are available that are especially valuable in cases like this. An easy test that helps differentiate a retinal problem from a media problem is a potential acuity meter (PAM). A PAM is a laser interferometer that projects a pattern onto the patient's retina through his dilated pupil.

The patient reads increasingly smaller letters, much like a Snellen's chart. The better the retinal condition, the smaller the letters the patient can read. The wavelength of the laser and the interference pattern generated allows these letters to penetrate the cataract. Thus a PAM gives a good estimate of retinal function. Jewel read the 20/40 line OD with the PAM and 20/20 OS, indicating that if we had her cataract removed, she could only expect 20/40 resultant VA OS.

The PAM result also proved that the macular condition contributed to the decreased VA at least as much as the cataract did. To get a better handle on the nature of the retinal pathology, I ordered an intravenous fluorescein angiogram (IVFA), which essentially turned out normal.

It found no edema or fluid leakage, which ruled out CSC, macular edema, PED and SRNVM. The absence of blockage or hypofluorescence indicated that no hemorrhages or holes were present.

Jewel had a PSC and an ERM OD, each of which accounted for equal amounts of her diminished VA. Fortunately, both conditions were operable but the remaining question was whether both needed correcting and if so, which should we correct first?

I used the Retinal Thickness Analyzer (RTA) to help answer that question. The RTA showed two focal areas of significant retinal thickening and a confined area of retinal disorganization (Fig 1). The thickened areas were juxtafoveal and showed why Jewel was in such visual discomfort. The ERM was not large but had two significant thick edges, which increased the chance for a successful membrane peel surgery.

The most common side effect of a vitreo-retinal surgical procedure is secondary cataract formation. The most common side effect of a cataract extraction (in cases such as this) is macular edema, which could worsen the retinal condition.

Armed with this knowledge, we decided together to first remove the epiretinal membrane and then to extract the cataract at a later, more appropriate time.

Welcoming a happy end

A retinal surgeon performed a membrane peel and vitrectomy on Jewel a few weeks later. The surgery went well and she had an uncomplicated postoperative course. Three months later, another surgeon removed the cataract in Jewel's right eye, which by now had increased to a 3+ PSC. Her final outcome was excellent. Jewel now sees 20/25 OD and 20/20 OS. More importantly, she's experiencing no more glare and can function normally again. As she put it, "I feel like I have my life back!"

Not just book learnin'

Cases such as Jewel's force us to use our differential diagnosis capabilities and to use available technology to identify the proper diagnosis and the best treatment. All the answers can't always be found in a textbook. In my opinion, that's what makes eye care so much fun.

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