[Optokinetic afternystagmus: its classification, sexual difference and relation to age in normal subjects].

Optokinetic afternystagmus, or OKAN, was investigated in 147 normal subjects (69 males and 78 females aged 20-78) for the purpose of obtaining the normal duration range and total number of beats in OKAN of the 1st phase. OKAN was recorded nystagmographically with the eyes open in darkness immediately after the sudden cessation of horizontal optokinetic stimulation with a constant speed of 60 degrees/sec. for 45 sec. The duration data for OKAN of the 1st. phase were distributed in a very wide range, between 0 and 180 sec., in all 294 samples. Therefore, the author arbitrarily divided the times into 3 categories: hypo-response with a duration below 10 sec., middle response above 10 sec. but below 60 sec. and hyper-response above 60 sec. OKAN were classified into 6 groups, with 3 subgroups, based on durations of OKAN of the 1st. phase, as results varied widely. 1. Classified OKAN groups and their rates: symmetric bilateral middle response (1a) was 10.9%, asymmetric bilateral middle response (1b) 15.0%, symmetric bilateral hyper-response (2a) 2.7%, asymmetric bilateral hyper-response (2b) 1.4%, bilateral hypo-response (bilateral no response (3a) and others (3b)) 25.2%, unilateral hypo response with contralateral middle response (4) 31.3%, unilateral hypo-response with contralateral hyper-response (5) 4.1%, and, unilateral middle response with contralateral hyper-response (6) 9.5%. 2. Classified OKAN groups for each sex and in different age groups: Generally, characteristic changes in the rate of classified OKAN for each sex and in different age groups could not be detected, for example, bilateral hypo-response (3a and 3b) appeared in all age groups from different decades. 3. The mean value of the maximal velocity in the slow phase of OKAN of the 1st. phase was 8.6 degrees/sec, the mean value of the total number of beats in OKAN of the 1st. phase was 22.8 and the average durations of OKAN of the 1st phase, to the right and to the left, were 27.3 sec and 21.7 sec., respectively. OKAN of the 2nd phase appeared in 9 (6.1%) but OKAN of 3rd phase was not observed in any of the subjects.