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Follow assessment rules for detecting glaucoma
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PHILADELPHIA – “The days of detecting glaucoma by IOP are over,” Robert D. Fechtner, MD, said here at the PRIMARY CARE OPTOMETRY NEWS Symposium. In an Allergan-sponsored presentation, Dr. Fechtner and Ian B. Gaddie, OD, FAAO, offered new perspectives in the detection and treatment of glaucoma, focusing specifically on the use of perimetry.
“We need to look at the optic nerve,” Dr. Fechtner continued. “Glaucoma is optic neuropathy that causes vision loss. The optic nerve exam is where we find glaucoma.”
Five rules for assessing the optic disc
Dr. Gaddie went over the five “Rs” for assessing the optic disc in glaucoma. First, he said, the practitioner should observe the scleral ring to identify the limits of the optic disc and its size. “Big discs have big cups,” he said.
The practitioner should then identify the size of the rim using the “ISNT” rule: the rim is thickest inferiorly, then superiorly, then nasally, then temporally. He emphasized the importance of assessing the rim rather than the cup. “The cup is just the absence of rim,” he said.
Another important aspect of optic disc assessment is to examine the retinal nerve fiber layer. Dr. Gaddie recommended the use of a 78-D lens with a red-free filter. He said the GDx (Carl Zeiss Meditec, Dublin, Calif.), the HRT (Heidelberg Engineering, Vista, Calif.) and OCT (Carl Zeiss Meditec) also enable the practitioner to evaluate nerve fiber layer.
The next rule is to examine the region of peripapillary atrophy, which worsens in at-risk eyes.
Finally, the practitioner should look for retinal and optic disc hemorrhages.
Rules for visual field interpretation
Dr. Fechtner also discussed rules for visual field interpretation. The first rule is to be sure that the right test was used, he said. The correct test is determined based on the test strategy, the test stimulus size, the field size, pupil size, refractive error and patient’s age. “You need to be sure this information is correct,” he said.
The second rule is to check the reliability of the field, which is based on reliability indices, the false positive rate (FP), false negative rate (FN) and fixation losses (FL).
Dr. Fechtner discussed what is considered acceptable in terms of false positive and false negative rates. He said that a false negative rate of greater than 25% should warrant caution, and that a false positive rate of greater than 33% is unacceptable.
The third rule, Dr. Fechtner said, is to review probability plots, looking for data points that fall below 0.5% reliability. The practitioner should also evaluate mean deviation, pattern standard deviation and glaucoma hemifield.
Rule number four requires the optometrist to evaluate the retinal nerve fiber layer pattern of vision loss, noting that not all nerve fiber layer loss is glaucomatous.
Finally, the practitioner should reaffirm the diagnosis. This is accomplished by re-evaluating the retina and optic nerve, seeking consistency with the visual field and by repeating the test if necessary.