**Question:** A total of 5000 patients of glaucoma are identified and surveyed, including interviews regarding family history of glaucoma. Such a study design is called

A. Cross-sectional study
B. Case-control study
C. Prospective study
D. Retrospective study

**Correct Answer:** D. Retrospective study

**Core Concept:** Retrospective studies involve collecting and analyzing data from patients' medical records, usually from a specified time period. In this case, the study design is used to investigate the prevalence and risk factors of glaucoma.

**Why the Correct Answer is Right:** A retrospective study is right for this question because it involves reviewing the medical records of patients with glaucoma who have already been diagnosed and treated. The data collection occurs after the fact, making it a retrospective study. This type of study is useful for assessing the prevalence of glaucoma and understanding potential risk factors associated with the condition.

**Why Each Wrong Option is Incorrect:**

A. Cross-sectional study (A): This study design examines participants at a single point in time, which is not suitable for this question focusing on past events and patient data.

B. Case-control study (B): This study design involves comparing cases (patients with the disease) with controls (patients without the disease). In this question, we are focused on glaucoma patients and their medical history, not comparing two groups.

C. Prospective study (C): Prospective studies monitor participants over time, which is not suitable for this question as it requires examination of past data and risk factors related to glaucoma.

**Clinical Pearl:** Retrospective studies can be valuable tools for understanding diseases and their risk factors. However, they are limited by the quality and accuracy of the available data, as well as potential recall bias. To ensure the best results, it is essential to use well-documented medical records and ensure that the study population is representative of the target population.