Screening Programs — MCQs
Which of the following is NOT a core component of the WHO's global STI control strategy?
Specificity of a diagnostic test is defined as:
What is the correct formula for calculating the positive predictive value (PPV) of a screening test?
Under NPCB, screening of school children is first done by -
Which measure indicates the diagnostic power of a test to correctly identify those with a disease?
Which of the following procedures is not typically covered by the National Programme for Control of Blindness (NPCB) for reimbursement of surgery done by a non-governmental organization (NGO) eye hospital?
All of the following are the targets for National Programme for Control of Blindness (NPCB), EXCEPT:
Which of the following is a true statement about screening tests for genetic diseases?
In primary open-angle glaucoma (POAG), which of the following findings is NOT typically seen?
What is the gold standard method for visualizing the periphery of the retina?
Screening Programs Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is NOT a core component of the WHO's global STI control strategy?
- A. Case management
- B. Universal mandatory screening (Correct Answer)
- C. Strategic information systems
- D. Prevention services
Explanation: ***Universal mandatory screening*** - While screening is part of STI control, **universal mandatory screening** for all STIs in the general population is not a core component of the WHO's strategy due to feasibility, cost, and ethical considerations. - The strategy emphasizes **targeted screening** for at-risk populations and opportunistic screening. *Case management* - **Case management**, including accurate diagnosis and effective treatment, is a critical component for managing current infections and preventing further transmission. - This involves syndromic or etiologic approaches to treatment and partner notification. *Strategic information systems* - **Strategic information systems** are essential for monitoring trends, evaluating interventions, and informing policy decisions related to STI control. - This includes surveillance data, program monitoring, and research. *Prevention services* - **Prevention services** are a cornerstone of the WHO's strategy, aiming to reduce the incidence of new infections. - These services encompass health education, condom promotion and distribution, vaccination, and pre-exposure prophylaxis (PrEP).
Question 2: Specificity of a diagnostic test is defined as:
- A. 0.95 (Correct Answer)
- B. 0.05
- C. 0.4
- D. 0.8
Explanation: ***0.95*** - **Specificity** is the proportion of individuals without disease who test negative, calculated as **TN/(TN+FP)**. - A specificity of 0.95 (95%) indicates an excellent test that correctly identifies 95% of healthy individuals as negative. *0.05* - This value represents the **false positive rate** (1 - specificity), not specificity itself. - A specificity of 0.05 would mean only 5% of healthy individuals test negative, indicating a very poor test. *0.4* - This value is too low for specificity and could represent other test parameters like **positive predictive value**. - A specificity of 0.4 would incorrectly classify 60% of healthy individuals as positive, making the test clinically unreliable. *0.8* - This value typically represents **sensitivity**, which is the proportion of diseased individuals who test positive. - **Sensitivity** is calculated as **TP/(TP+FN)**, which is different from specificity that focuses on healthy individuals.
Question 3: What is the correct formula for calculating the positive predictive value (PPV) of a screening test?
- A. True positives / (True positives + False negatives)
- B. False positives / (False positives + True negatives)
- C. True positives / (True positives + False positives) (Correct Answer)
- D. True negatives / (True negatives + False negatives)
Explanation: ***True positives / (True positives + False positives)*** - **Positive predictive value (PPV)** indicates the probability that a patient who tests positive actually has the disease. - It is calculated by dividing the number of **true positives** (correctly identified positive cases) by the total number of positive test results (**true positives + false positives**). *True positives / (True positives + False negatives)* - This formula represents the **sensitivity** of a test, which is the proportion of actual positive cases that are correctly identified. - Sensitivity measures the ability of a test to correctly identify individuals with the disease. *False positives / (False positives + True negatives)* - This formula represents **1 - specificity**, or the **false positive rate**. - **Specificity** is the proportion of actual negative cases that are correctly identified as negative. *True negatives / (True negatives + False negatives)* - This formula represents the **negative predictive value (NPV)**, which is the probability that a patient who tests negative actually does not have the disease. - NPV is calculated by dividing the number of **true negatives** (correctly identified negative cases) by the total number of negative test results (**true negatives + false negatives**).
Question 4: Under NPCB, screening of school children is first done by -
- A. Ophthalmologic assistant
- B. Medical officer
- C. Village health guide
- D. School teachers (Correct Answer)
Explanation: ***School teachers*** - Under the **National Programme for Control of Blindness (NPCB)**, screening of school children follows a **three-tier approach**. - **School teachers** are trained to conduct the **first level/initial screening** using simple vision tests like **Snellen charts**. - They identify children with potential vision problems and refer them for further detailed assessment. - This approach maximizes coverage as teachers have regular contact with children and can screen large numbers efficiently. - The NPCB specifically includes **teacher training modules** for basic vision screening as part of the School Eye Screening Programme. *Ophthalmologic assistant* - Ophthalmic assistants/paramedical workers conduct the **second level screening** - the detailed assessment of children referred by teachers. - They perform comprehensive vision testing and identify specific refractive errors and eye conditions. - They are not the first point of contact in school screening due to resource limitations and the scale of screening required. *Medical officer* - Medical officers and ophthalmologists are involved in the **third tier** - providing diagnosis, treatment, and management of identified cases. - They handle complex cases, prescribe spectacles, and provide surgical interventions when needed. - They also supervise the overall program but do not conduct initial mass screening. *Village health guide* - Village health guides work primarily in community settings for general health promotion and basic healthcare. - While they contribute to community health awareness, they are not specifically involved in the structured school eye screening program under NPCB.
Question 5: Which measure indicates the diagnostic power of a test to correctly identify those with a disease?
- A. Negative predictive value
- B. Specificity
- C. Sensitivity (Correct Answer)
- D. Positive predictive value
Explanation: ***Positive predictive value*** - It refers to the probability that subjects with a positive test result truly have the disease, highlighting the test's **diagnostic accuracy** [1]. - A high positive predictive value indicates that the test is effective at diagnosing the disease in the population tested. *Sensitivity* - Sensitivity measures the ability of a test to correctly identify those with the disease (true positives), but does not account for the test result's predictive capability [1]. - It is important for screening, but **not directly the diagnostic power** for those already tested. *Negative predictive value* - This indicates the probability that subjects with a negative test result truly do not have the disease, focusing on true negatives rather than correct diagnosis of the condition [1]. - While informative, it does not assess the ability to correctly diagnose the disease when the result is positive. *Specificity* - Specificity is the measure of a test's ability to correctly identify those without the disease (true negatives), not diagnosing the disease accurately among those tested [1]. - It is essential for determining false positives but not for assessing the overall diagnostic power of a test. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 253-254.
Question 6: Which of the following procedures is not typically covered by the National Programme for Control of Blindness (NPCB) for reimbursement of surgery done by a non-governmental organization (NGO) eye hospital?
- A. Cataract surgery
- B. Pan retinal photocoagulation for diabetic retinopathy
- C. Syringing and probing of the nasolacrimal duct (Correct Answer)
- D. Trabeculectomy surgery
Explanation: ***Syringing and probing of the nasolacrimal duct*** - While important for lacrimal drainage issues, procedures like **syringing and probing** are generally considered minor and less vision-restoring compared to the major surgeries targeted by the **NPCB**. - The **NPCB** focuses on interventions for leading causes of blindness, primarily **cataract** and other significant vision-threatening conditions, which this procedure typically isn't. *Cataract surgery* - **Cataract surgery** is a cornerstone of the **NPCB's** efforts, as cataracts are the leading cause of reversible blindness. - Reimbursement for **cataract surgery** is a primary objective to improve access and reduce the burden of blindness. *Pan retinal photocoagulation for diabetic retinopathy* - **Diabetic retinopathy** is a major cause of preventable blindness, and **pan retinal photocoagulation (PRP)** is a key intervention to preserve vision. - The **NPCB** includes procedures for **diabetic retinopathy** management due to its significant public health impact. *Trabeculectomy surgery* - **Trabeculectomy** is a surgical procedure for **glaucoma**, which is another significant cause of irreversible blindness. - The **NPCB** includes interventions for **glaucoma** given its severe vision-threatening nature and the need for surgical management in many cases.
Question 7: All of the following are the targets for National Programme for Control of Blindness (NPCB), EXCEPT:
- A. Development of 50 pediatric ophthalmic units
- B. Increase cataract surgery rate to 450 operations per lakh population
- C. Intraocular lens implantation in more than 80 percent cataract surgery cases
- D. 100% coverage of vitamin A prophylaxis doses from 9 months to 3 years of age (Correct Answer)
Explanation: ***100% coverage of vitamin A prophylaxis doses from 9 months to 3 years of age*** - This objective is typically associated with the **Reproductive and Child Health (RCH) program** and efforts to combat **Vitamin A deficiency**, not directly with the core targets of the National Programme for Control of Blindness (NPCB). - While vitamin A deficiency can lead to blindness, the NPCB's primary focus has historically been on treatable causes of blindness such as **cataract** and **refractive errors**. *Development of 50 pediatric ophthalmic units* - The NPCB aims to **strengthen ophthalmic services**, and the development of specialized pediatric units is a crucial component to address childhood blindness. - This target aligns with the program's focus on **preventing and treating blindness** across all age groups, including children. *Increase cataract surgery rate to 450 operations per lakh population* - **Cataract** is the leading cause of blindness in India, and increasing the **cataract surgery rate** is a key strategic objective of the NPCB to reduce the burden of preventable blindness. - This specific numerical target reflects the program's commitment to **scaling up surgical interventions**. *Intraocular lens implantation in more than 80 percent cataract surgery cases* - The NPCB emphasizes not just the quantity but also the **quality of cataract surgeries** performed. - Promoting **intraocular lens (IOL) implantation** in a high percentage of cases ensures better visual outcomes and rehabilitation for patients.
Question 8: Which of the following is a true statement about screening tests for genetic diseases?
- A. Screening test has better accuracy than diagnostic test
- B. It is always invasive
- C. It defines risk of transmission of disease to the child (Correct Answer)
- D. Screening requires genetic mapping
Explanation: ***Correct: It defines risk of transmission of disease to the child*** - Genetic screening aims to identify individuals or couples at risk of passing on **heritable genetic conditions** to their offspring. - This information helps in **family planning** and provides prenatal diagnostic options if the risk is high. - This is the **primary purpose** of genetic screening programs. *Incorrect: Screening test has better accuracy than diagnostic test* - **Screening tests** are designed to be broad and detect potential risks, often with lower specificity and sensitivity than diagnostic tests. - **Diagnostic tests** are typically more accurate and definitive, confirming the presence or absence of a disease after a positive screening result. *Incorrect: It is always invasive* - Many genetic screening tests, such as **non-invasive prenatal screening (NIPS)** from maternal blood or carrier screening via saliva, are non-invasive or minimally invasive. - While some diagnostic tests like **amniocentesis** or **chorionic villus sampling** are invasive, screening itself is not universally so. *Incorrect: Screening requires genetic mapping* - **Genetic mapping** refers to determining the relative positions of genes on a chromosome, which is a research tool for understanding genome organization. - Genetic screening primarily involves testing for specific mutations or chromosomal abnormalities, not creating a comprehensive genetic map of an individual.
Question 9: In primary open-angle glaucoma (POAG), which of the following findings is NOT typically seen?
- A. Bayoneting sign (arteriovenous crossing changes)
- B. Peripapillary atrophy
- C. Horizontal cupping of the optic disc
- D. Macular edema (Correct Answer)
Explanation: ***Macular edema*** - **Macular edema** is characterized by fluid accumulation in the fovea or retina, causing blurry vision and metamorphopsia. - While it can occur in conditions like **diabetic retinopathy** or **uveitis**, it is **not a typical finding in POAG**, which primarily affects the optic nerve. *Horizontal cupping of the optic disc* - **Horizontal cupping** (or vertical elongation of the optic cup) is a common sign of **glaucomatous damage**, reflecting the loss of retinal ganglion cells. - This morphological change suggests the progression of optic nerve atrophy. *Bayoneting sign (arteriovenous crossing changes)* - The **bayoneting sign**, where blood vessels appear to dip below the optic disc margin and then sharply bend, is a feature of **advanced glaucomatous cupping**. - It indicates significant loss of optic nerve tissue and is often associated with deeply excavated optic discs. *Peripapillary atrophy* - **Peripapillary atrophy** (PPA) refers to areas of RPE and choroidal atrophy surrounding the optic disc, commonly seen in glaucoma. - While its presence and extent may correlate with **glaucoma severity**, it is a recognized clinical feature of the disease.
Question 10: What is the gold standard method for visualizing the periphery of the retina?
- A. Direct ophthalmoscopy
- B. Indirect ophthalmoscopy (Correct Answer)
- C. Retinoscopy
- D. USG
Explanation: ***Correct: Indirect ophthalmoscopy*** - This method uses a **condensing lens** and a bright light source to provide a **wide-field, stereoscopic view** of the retina, making it ideal for visualizing the periphery. - It allows for examination even through some media opacities and is particularly useful for detecting peripheral retinal tears or detachments. - Provides a **field of view of 25-40 degrees** compared to only 5-10 degrees with direct ophthalmoscopy. *Incorrect: Direct ophthalmoscopy* - Provides a **highly magnified but narrow field of view**, making it difficult to systematically scan and visualize the entire peripheral retina. - It offers an **upright, monocular image** with limited depth perception, which is not optimal for assessing the three-dimensional structures of the retinal periphery. *Incorrect: Retinoscopy* - This is an objective method used to **determine the refractive error** of an eye, not for direct visualization of the retinal structures. - It involves observing the reflection of light from the retina as the examiner moves a light source across the eye. *Incorrect: USG* - **Ultrasound (USG)** is primarily used to visualize ocular structures when direct visualization is obscured by dense media opacities (e.g., severe cataracts, vitreous hemorrhage). - It provides 2D images and is not the gold standard for **routine, high-resolution visualization** of the retinal periphery when a clear view is obtainable.
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