CLINICAL CHALLENGES
The Pits
Clinical findings had O.D.s questioning a diagnosis, but a good look revealed the truth.
By Eric Schmidt, O.D.

Now that we're firmly entrench-ed in the 21st century, we accept the fact that technology plays a huge role in managing glaucoma. But, as this case points out, there's still no substitute for careful observation of the optic nerve head (ONH) with our own two eyes.

Stating the facts

At the first encounter, Alice appeared as the classic glaucoma suspect. She had a few of the common risk factors for the disease; namely vascular dysfunction and a strong family history along with reportedly asymmetric ONHs. But she had more than a few factors pointing against her having glaucoma. These included her relatively young age, borderline intraocular pressure (IOP) and small ONH.

Alice was 60 years old when her primary O.D. first referred her to me. An ophthalmologist had treated Alice for primary open-angle glaucoma (POAG) for the past 16 months, but her O.D., who had examined her over the past six months, wasn't so sure Alice had the disease. He asked me to examine her and give him my thoughts.

As I said, Alice did have some risk factors for POAG. Her sister and uncle were being actively treated for POAG and her mother, now deceased, had POAG as well. Alice took amlodipine besylate (Norvasc) and furosemide (Lasix) for hypertension and had previously used hydrochlorothiazide and triamterene (Maxzide).

In addition Alice used loratadine (Claritin) daily for allergies and had rather severe breathing problems for which she took beclomethasone/dipropionate (Vancenase) and an ipratropium bromide inhaler (Atrovent) as needed for relief. She had previously been prescribed hydroxychloroquine (Plaquenil) for arthritis but was currently only using ibuprofen.

In his referral letter to me, Alice's primary O.D. included some additional pertinent information. He stated that her initial IOP ran between 21 mm Hg to 24 mm Hg untreated. He noted disk asymmetry of .3/.3 OD and .5/.5 OS. He ran visual fields tests on two occasions and the results were normal both times.

Alice's primary optometrist also told me that when she first saw him she was using levobun-olol hydrochloride 0.5% (Betagan Liquifilm) OU b.i.d. as prescribed by an ophthalmologist. The O.D. justifiably discontinued the drops for two good reasons: First, he wasn't convinced that Alice had glaucoma and second, even if she did, the beta blocker was contraindicated given Alice's respiratory dysfunction.

Facing a classic quandary

Alice's O.D. followed her for about six months without instituting further treatment. On the levobunolol, her IOP was 19 mm Hg to 20mm Hg. Without drops, her IOP ranged between 21 mm Hg and 24 mm Hg. But given Alice's family history, the O.D. felt that additional testing was necessary. He referred Alice to me to see whether I could provide any additional insight.

When I first saw Alice, her history was essentially unchanged from what I've mentioned with one notable exception: She said she was far less dependent on the beclomethasone/dipropionate and the ipratropium bromide inhaler since she stopped using the levobunolol hydrochloride drops. She had no complaints with her eyes other than occasional itching and tearing, but she said that she hoped I could clear up some of the questions about the glaucoma.

Alice's visual acuity (VA) was 20/20 OU with and without glasses. Pupils were 5mm round and briskly reactive with no afferent pupil defect OU. External and slit lamp exams OU were normal as well. I measured her IOP to be 22 mm Hg in each eye at 3:50 p.m.

Before dilating her, I placed a Posner 4 mirror gonioscopy lens on her eyes and examined the anterior chamber angle. The angles were open and I graded them at 3 to 4, 360 degrees OU but did note 1+ peripheral anterior synechiae scattered throughout the angles OU. I had my assistant put some dilating drops in Alice's eyes while I left to see other patients, thinking to myself that Alice is most likely an ocular hypertensive who wouldn't need treatment at this time.

Recognizing the pit

Before I examined Alice's ONHs I took a closer look at her visual field printouts from her optometrist. They weren't absolutely normal; there were indeed some spots of decreased sensitivity scattered through Bjerrum's area superiorly and inferiorly in both eyes. But the answer to this clinical quandary was as clear as a bell once I looked at her ONH with a 78D lens.

The first thing that struck me in Alice's OD was the size of her ONH. I estimated it at less than 1.8 mm in diameter, which is small and at first glance it seemed to have a larger cup-to-disc ratio (C/D) than the other doctor noted. After critically viewing the neuroretinal rim I noticed that the C/D was wh~ .3/.3 but that there was a large defect out of the rim at 2:00 (Fig. 1). This was an optic pit, not a classic notch. The rest of the ONH and retina was normal OD. The ONH OS was also small in diameter but had a larger C/D, which I estimated at .45/.5. I didn't note any focal notches or nerve layer dropout OS.

The skinny on the pit

The defect that I noticed on Alice's neuroretinal rim is more appropriately called an acquired pit of the optic nerve (APON). It isn't a classic optic pit, which is a congenital coloboma. A true optic pit is a complete absence of tissue caused by a defect in development of that particular tissue.

An APON, or pseudopit as it's sometimes called, develops in progressive glaucoma. An APON is a large focal defect in the neuroretinal rim that typically develops rather abruptly. The etiology of APON is most likely ischemia of the underlying retina and choroid. The vascular insufficiency leads to atrophy of that portion of the ONH and the resultant APON is the ophthalmoscopic manifestation of this poor local perfusion. A simple way to think of APON is as a large focal notch of the neuro-retinal rim.

An APON is basically pathognomonic for glaucoma. More importantly though, it indicates uncontrolled glaucoma regardless of the IOP. APON develops because of poor perfusion to the ONH. Thus, when you see one, you need to lower the patient's IOP further. APONs are generally associated with a concomitant visual field defect, although early in its development the visual field may not yet be affected.

Coming to terms

Obviously the presence of the APON cemented my decision that Alice did have POAG OU. I performed retinal thickness testing, which showed the APON OD as well as an attenuated nerve fiber layer and focal changes at the neuro-retinal rim OD, which confirmed the diagnosis.

I recommended treating both eyes because of the larger C/D OS (even though the retinal thickness analysis was relatively normal OS). I also suggested a target IOP of about 15 mm Hg -- a 30-percent drop from the highest IOP. I also agreed that a non-selective beta blocker probably wasn't in Alice's best interest. Her IOP didn't respond well to prostaglandin analog therapy, but I last heard that she's being treated with Alphagan-P OU t.i.d. and that her IOP remains steady around 16 mm Hg.

Obviously her primary O.D. will continue to follow her for any signs of progression and I'll perform a retinal thickness analysis annually. So far, Alice's glaucoma seems well controlled without side effects from her therapy.

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