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R. Asaoka, D. Crabb, T. Yamashita, R. Russell, Y. Wang, D. Garway-Heath; Integrated Visual Field Measures Provide a Better Estimate of Patient Visual Field Severity Than Mean Deviation in the Better Eye. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4330.
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The Humphrey Mean Deviation (MD) and Visual Field Index (VFI) describe visual field (VF) loss severity in an eye rather than a patient. These monocular measures, particularly in the better eye, are typically used in the clinic to gauge the severity of patient impairment. This study tests the hypothesis that a measure based on the Binocular Integrated Visual Field (IVF) [1,2] provides a different estimate of a patient’s VF severity than a ‘per eye’ measure (MD in the better eye).
Humphrey visual field charts (24-2 SITA standard) from 68 consecutive patients in a normal tension glaucoma clinic were retrospectively examined (mean age: 66, range [31, 88] years). The better MD from the two eyes was recorded. IVFs were constructed for each patient by merging monocular VFs. An average of total deviation values in the IVF generated the IVF MD. The differences between better-eye MD and IVF MD were assessed.
The average IVF MD was significantly better than average better-eye MD (mean difference 1.3 dB, 95% confidence interval [CI]: 1.0 to 1.7 dB, P<0.001). Twenty-five percent of the patients had an IVF MD that was at least 2dB healthier than the MD in the better eye (95% CI: 15 to 37 %). There was significant linear association between the differences in better-eye and IVF MD against the severity of VF defect (P<0.001, R2=0.44).
Using the MD in the better eye gives the impression that the patient’s VF loss severity is worse than if a binocular measure is used. These differences are more pronounced in patients with advanced defects and especially where there is asymmetry in the scotoma between eyes. The IVF offers a rapid assessment of a patient’s VF severity without extra binocular testing. Crabb DP et al. Br J Ophthalmol. 2004 Sep;88:1191-6.  Crabb DP et al. Br J Ophthalmol. 1998;82:1236-41.
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