Fig. 10. Gradual decline in visual acuity with increasing age.

Evaluating visual acuity of young, middle-aged, old, and very old fish, studied by determining the maximal spatial frequency that causes an optokinetic response, discloses that all age groups retain visual acuity, yet a gradual reduction can be seen in function of age. Data are depicted as mean ± standard error of mean, n ≥ 20, statistical significance between different age groups is indicated using different letters.