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Parapapillary ‘beta zone’ should be watched for progression, studies suggest
A specific area of the parapapillary region, if closely followed, could be predictive of glaucomatous change, says glaucoma specialist.
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MANNHEIM, Germany — Two physiologically distinct areas of peripapillary retina can be differentiated and evaluated by astute glaucoma clinicians to assess glaucomatous progression, according to a German specialist. Jost B. Jonas, MD, discussed the usefulness of various optic nerve features in predicting structural changes and advancing disease.
“There have been several studies published suggesting that a large beta zone may be a risk factor for progression … and that patients with a large beta zone might need more aggressive treatment to prevent progression than patients without a beta zone,” he said.
Parapapillary atrophy can be differentiated into an outer “alpha” and inner “beta” zone that borders the optic disc, he explained. The outer alpha zone may be characterized by irregular hypo- and hyperpigmentation, followed by the beta zone, which reveals sclera at the optic disc border as well as large visible choroidal vessels.
Study correlates features, progression
Dr. Jonas added that this progression is confirmed by a study in which the group with glaucomatous progression had a significantly larger beta zone than the non-progressive group. In that study, a total of 357 glaucoma patients were differentiated into those showing glaucomatous visual field progression and those not showing progression.
Morphological features such as peripapillary retina, neural rim area, disc size and vessels were examined for possible correlation to glaucomatous progression.
Disc size
Dr. Jonas ruled out optic disc size, except in high myopia, as a feature that could be associated with either susceptibility or glaucomatous progression, though he acknowledged conflicting studies on this matter.
“First, studies have shown that disc drusen and non-arteritic anterior ischemic optic neuropathy are usually associated with a small optic disc. Second, histological studies have shown that eyes with small optic discs have fewer photoreceptors and optic nerve fibers, suggesting susceptibility for glaucoma,” he said.
Further, some studies correlated larger discs to normal pressure glaucoma and medium-sized optic discs to high pressure glaucoma, but no such correlation could be made in the previously mentioned study. “The progressive group, compared with the stable group, did not differ significantly in the area of the optic disc, again indicating that disc size is not a risk factor for glaucoma,” Dr. Jonas said.
Myopic discs are an exception, and their size could possibly suggest susceptibility.
“There’s an hypothesis that the myopic stretching of the globe and the disc may be a risk factor for glaucoma and possibly be a risk factor for progression. This has been shown by histology, where the emmetropic glau coma eye has a different histology … compared to the highly myopic glaucoma eye, where the peripapillary region is composed entirely only of sclera and retinal nerve layer with no retinal pigment epithelium and choroidal structures,” Dr. Jonas said.
Arterial diameter
Decreased caliber of arterial vessels is clearly associated with glaucoma but not as an indicator of susceptibility to glaucoma. Progressive narrowing of vessels, though, can be a feature associated with progressive worsening of glaucoma, he explained.
“The continuing diminution of retinal arteries is not a risk factor, but a marker for progression. The study on progression of visual field loss has shown that the stable group, compared to the progressive group, did not differ in the diameter of the retinal arteries at baseline, suggesting that a small vessel diameter alone is not a risk factor for progression,” Dr. Jonas said.
Neural rim
Neural rim loss may be indicative of future progression. In this study, the patients with greater baseline loss were associated with the patients demonstrating further glaucomatous progression.
“The … progressive group had at baseline of the study significantly lower neural rim areas and significantly greater visual field defects compared to the non-progressive group, suggesting that the more advanced glaucoma, the higher might be the risk for glaucoma progression,” Dr. Jonas said.
Disc hemorrhage, he added, is very predictive of disease progression.
For Your Information:
- Jost B. Jonas, MD, can be reached at (49) 621-383-2242; fax: (49) 621-383-3803; e-mail: jost.jonas@ augen.ma.uni-heidelberg.de. Dr. Jonas has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.