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Binocular, monocular visual field tests show defects differently
Researchers evaluated the distribution and progression of glaucomatous visual field defects with binocular vision and frequently found defects at the Mariotte blind spots in the central visual field and around the bitemporal areas in the periphery.
To evaluate the defects in the central and peripheral visual fields, researchers used the Humphrey 24-2 tests for both eyes and the Binocular Humphrey Esterman VF test (EVFT) (Carl Zeiss Meditec).
A total of 167 patients with glaucoma were enrolled, and all received the Humphrey Swedish Interactive Threshold (SITA)-Standard 24-2 (Carl Zeiss Meditec) visual field test for both eyes. A subset of 77 patients was also tested by the EVFT.
The Humphrey Field Analyzer II perimeter (Carl Zeiss Meditec) was used for all visual field tests, including both monocular and binocular. The monocular visual field test used the monocular Humphrey 24-2 test and the monocular EVFT. The binocular visual field test used the binocular EVFT, according to researchers.
For data analysis, “the monocular Humphrey 24-2 results were merged to produce a binocular integrated visual field, which was calculated by the Best Location Algorithm with each patient’s best point-by-point monocular sensitivity,” the researchers wrote.
Researchers classified visual field loss into stages by the Esterman Disability Score (EDS). Visual field loss of the earliest stage had an EDS between 90 and 100.
The sample mean deviation for the Humphrey 24-2 was -10.9 dB OD and -10.6 dB OS. The sample mean for the Humphrey 24-2 EDS was 74.2% for the right eye and 75.3% for the left eye.
Researchers found no significant difference in the Humphrey 24-2 MD and EDS between the right and left eyes.
The sample mean for the monocular Esterman EDS was 81.9% for the right eye and 78.8% for the left eye. No significant difference in the EDS was seen between both eyes.
Researchers primarily observed defects around the Mariotte blind spot and the Bjerrum areas in the central visual field, which extended to the peripheral visual field as the stage progressed. Visual field defects were frequently observed at the bitemporal and Bjerrum areas in early stages and extended through the entire visual field as the stage advanced.
Particularly at the earliest stage of glaucoma, the two locations corresponding to the Mariotte blind spots showed significantly higher percentages of patients with abnormality, they wrote.
Researchers added that defects in those locations will be more easily detected.
At the earliest stage, no abnormal peripheral nasal step visual field defects were observed at the six test locations where nasal step typically occurs.
They concluded that visual field defects with binocular vision appear to have different distribution and progression from previously reported results obtained with monocular vision in eyes with glaucoma. Topographical reproducibility with binocular methods must be confirmed, and a study involving a larger group should be conducted. – by Abigail Sutton
Disclosures: The authors have no relevant financial disclosures.
Perspective
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In clinical practice, monocular visual fields are important for glaucoma evaluation and disease management. However, to gauge glaucoma’s potential effect on activities of daily living, a binocular visual field assessment might be more helpful, as this better approximates the patient’s actual field of view.
Hashimoto and colleagues found that visual field defects determined while viewing binocularly were typically found around the physiologic blind spots centrally and the bitemporal areas peripherally. Their findings differ from other studies, suggesting more work needs to be done to understand the binocular peripheral visual field changes in glaucoma.
How will this study influence my clinical practice? First, it’s good to remember that vision loss in glaucoma happens outside 30 degrees. It’s easy to imagine peripheral bitemporal field loss affecting activities such as driving, so talk to your patients and their families about these activities. Will I start testing peripheral binocular fields? No. It’s already hard to get patients to do conventional fields, and they are important for disease management. I’m not going to cash in patient goodwill on a binocular test unless their symptoms suggest a problem. For now, my binocular field testing will entail holding up two monocular fields and using my imagination.