Prevalance of cataract at one point of time can be determined by –
**Core Concept**
The question is testing the understanding of the epidemiological measures used to determine the prevalence of a disease, specifically cataract. Prevalence is a type of disease frequency that measures the total number of cases of a disease in a population at a given time.
**Why the Correct Answer is Right**
Prevalence is typically determined by a cross-sectional study, which involves observing a representative sample of the population at a single point in time. This method provides a snapshot of the disease burden in the population. In the case of cataract, prevalence can be estimated by conducting a survey or a study that assesses the number of people with cataract in a given population at a specific point in time.
**Why Each Wrong Option is Incorrect**
**Option A:** Incidence refers to the number of new cases of a disease occurring within a population over a specified period, which is not relevant to determining prevalence.
**Option B:** Mortality rate measures the number of deaths due to a disease, which is not directly related to the prevalence of cataract.
**Option C:** Case fatality rate is the proportion of individuals who die from a disease among those who have been diagnosed with it, which is not a measure of disease frequency.
**Clinical Pearl / High-Yield Fact**
When estimating the prevalence of a disease, it's essential to consider the population's demographics, such as age and sex, as these factors can significantly impact the disease burden.
**Correct Answer: C. Cross-sectional study.**