Table 2.

Clinical subtypes of Usher syndrome

Characteristic features	Clinical subtype
	Type 1	Type 2	Type 3
Prevalence	1.5 per 100.000	2.2 per 100.000	0.1 per 100.000
Visual impairment onset
Night vision	First decade	Second decade	Variable, but within three decades
Central vision	Midlife	Midlife	Midlife
Auditory function	Congenitally profound deafness	Congenitally moderate-to-severe deafness	Progressive deafness in first or second decade
Vestibular function	Absent	Normal	Variable
Motor development	Delayed	Normal	Normal