Incidence and Prevalence

Incidence and prevalence are commonly used terms when talking about how frequently a disease occurs, however they convey different information.

Prevalence is the proportion of cases in the population at a given time rather than rate of occurrence of new (or newly diagnosed cases) within a specified period of time.

Incidence conveys information about the risk of contracting the disease, whereas prevalence indicates how widespread the disease is.

Inherited retinal diseases (IRDs) are the leading cause of vision loss in people of working age (16 to 64 years) and are estimated to affect 1 in every 3000 people. Taking into account all the different forms of Retinitis pigmentosa among the general population, the overall prevalence is variably reported as 1 case in 2500 to 1 case in 7000 persons. The prevalence of Leber congenital amaurosis (LCA) is estimated as 1 in 50,000 to 1 in100,000 people. Overall, LCA accounts for 5% of all retinal dystrophies and 20% of blindness in school age children.

The prevalence of Usher syndrome has been reported to range from 3.2 to 6.2 cases per 100,000 people. Usher syndrome was estimated to be responsible for 3%-6% of all childhood deafness and approximately 50% of all deaf-blindness.

The prevalence of Stargardt disease was estimated to be between 1 in 8000 and 1 in 10,000.

The prevalence of choroideremia is estimated to be 1 in 50,000 to 100,000 people and is thought to account for approximately 4 percent of all blindness despite being underdiagnosed due to its similarity to other eye disorders.

The exact prevalence of retinoschisis is currently unknown, but it is thought to affect between one in 5,000 to 20,000 people. Leber Hereditary Optic Neuropathy (LHON) affects approximately 1 in 50,000 people. The prevalence of Cone-rod dystrophy is estimated at 1 in 40,000.