Section 4.78 - Muscle function(a)Examination of muscle function. The examiner must use a Goldmann perimeter chart or the Tangent Screen method that identifies the four major quadrants (upward, downward, left, and right lateral) and the central field (20 degrees or less) (see Figure 2). The examiner must document the results of muscle function testing by identifying the quadrant(s) and range(s) of degrees in which diplopia exists.(b)Evaluation of muscle function.(1) An evaluation for diplopia will be assigned to only one eye. When a claimant has both diplopia and decreased visual acuity or visual field defect, assign a level of corrected visual acuity for the poorer eye (or the affected eye, if disability of only one eye is service-connected) that is: one step poorer than it would otherwise warrant if the evaluation for diplopia under diagnostic code 6090 is 20/70 or 20/100; two steps poorer if the evaluation under diagnostic code 6090 is 20/200 or 15/200; or three steps poorer if the evaluation under diagnostic code 6090 is 5/200. This adjusted level of corrected visual acuity, however, must not exceed a level of 5/200. Use the adjusted visual acuity for the poorer eye (or the affected eye, if disability of only one eye is service-connected), and the corrected visual acuity for the better eye (or visual acuity of 20/40 for the other eye, if only one eye is service-connected) to determine the percentage evaluation for visual impairment under diagnostic codes 6065 through 6066.(2) When diplopia extends beyond more than one quadrant or range of degrees, evaluate diplopia based on the quadrant and degree range that provides the highest evaluation.(3) When diplopia exists in two separate areas of the same eye, increase the equivalent visual acuity under diagnostic code 6090 to the next poorer level of visual acuity, not to exceed 5/200.73 FR 66550, Nov. 10, 2008, as amended at 83 FR 15321, Apr. 10, 2018 Authority: 38 U.S.C. 1155