<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by retinitis pigmentosa ? [/INST] Retinitis pigmentosa is one of the most common inherited diseases of the retina (retinopathies). It is estimated to affect 1 in 3,500 to 1 in 4,000 people in the United States and Europe. </s>