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Give special consideration of glaucoma imaging in patients with myopia
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WAILEA, Hawaii — The intersection of myopia and glaucoma creates a challenge for ophthalmologists, according to Angelo P. Tanna, MD, at Hawaiian Eye 2018.
“In patients who have high myopia, the optic disc is hard to read and has a glaucoma-like appearance and can fool us. The same is true for visual fields,” Tanna said.
The dual-edge sword is that myopia itself is a risk factor for glaucoma. One is twice as likely to have glaucoma if you have myopia, he added.
Even in moderate degrees of myopia up to -3.0 D the relative risk of glaucoma was about 1.6 to 1.7, he said.
The special considerations for myopia and glaucoma diagnosis imaging include artifacts and anomalies in retinal nerve fiber layer (RNFL); macular thickness; and axial myopia which is associated with a thinner retina, he said.
“With increasing axial myopia, the 3.46 mm circular RNFL scan diameter we are used to seeing increases as a function of axial length,” Tanna said.
The projected scan circle has a larger diameter because that circle is farther away from the optic disc margin.
For each diopter of myopia, the average RNFL thickness is about 1.3 µm thinner, according to Tanna.
In high myopia, there is a convergence in RNFL peaks. He said the peaks converge temporally and so with normative data it will project that the eye is abnormal as the thickness is not where the normal data says it should be.
“There is a normative database that corrects for this but it isn’t available in U.S. yet, but Zeiss is working on it,” Tanna said.
The problem with macular imaging is there are segmentation errors that occur there as well, he said.
The frequency of segmentation errors in previous research was 10%. Myopia was a significant risk factor for having segmentation error, he added.
Tanna concluded that the circumpapillary RNFL thickness is lower in myopia.
Further, the circumpapillary RNFL profile is different. The peaks shift temporally and the optic disc tilt and anomalous peripapillary architecture impact circumpapillary RNFL assessment. – by Abigail Sutton
Reference:
Tanna AP. Using OCT to manage glaucoma in myopia. Presented at: Hawaiian Eye; Jan. 13-19, 2018; Wailea, Hawaii.
Disclosure: Tanna is a consultant to Carl Zeiss Meditec.