Ophthalmological and cognitive examination

Bilateral monocular and binocular distance VA was measured with the best corrective lenses (BCVA) and without corrective lenses (uncorrected VA). All participants underwent measurement of binocular-corrected and monocular-corrected distant FVA using the AS-28 FVA measurement system (Kowa, Aichi, Japan). The FVA was defined as the average of all VA values measured during 60 s with the best distance correction. Measurements started with the Landolt ring size of the subject’s BCVA. Each Landolt ring was displayed in the device for 2 s. When the subject’s response was correct, the next Landolt ring size became smaller. If the response was incorrect or none, the next Landolt ring size became larger. The maintenance rate of FVA was calculated as follows: (lowest logarithm of the minimum angle of resolution (logMAR) VA score − FVA at 60 s) / (lowest logMAR VA score − baseline VA).

The KVA was measured using a KVA metre (AS-4; Kowa, Tokyo, Japan.) with the best distant correction as follows. The participants were instructed to look through the measuring window. They would detect the Landolt ring of 20/60 in a bright white circular shape. The Landolt ring moved towards the subjects from a 50 m distance at a velocity of 20, 40 and 60 km/h. The participants were asked to immediately respond by pressing a joystick when they identified the orientation of the Landolt ring. The results were expressed as decimal VA according to the distance of the participant’s response. After two practices to reduce mistakes due to unfamiliarity with the test, the participants carried out five trials at three velocities under binocular and monocular conditions, with a 1 min rest between each setting. If the participant’s answer was incorrect in all five trials, it was excluded from the analysis.

The stereo fly test (Stereo Optical Company Inc., Chicago, Illinois, USA) was performed at 40 cm to evaluate near stereopsis. The dominant eye was determined by the Rosenbach test. The Rosenbach method²¹ was used to determine which was the dominant eye. Subjects concealed small objects far away with their thumbs under binocular vision. When one of the eyes closed, the object hidden by the thumb became visible, which proved that the closed eye was the dominant eye.

The standard tear BUT was measured after the instillation of fluorescein sodium in the conjunctival sac with a test filter paper.²² The interval between the last complete blink and the appearance of the first corneal black spot in the stained tear film was measured three times, and the mean value was calculated. The cut-off value was 5/6 s. Cognitive status was evaluated with the MMSE-Japanese (MMSE-J, Nihon Bunka Kagakusha Co. Ltd, Tokyo, Japan).