Astigmatism - High-Yield MCQs for NEET PG / INICET

SECTION 1: Basic Concepts & Types

• A. Irregular curvature of the lens only
• B. Unequal refraction in different meridians of the eye ✓
• C. Increased axial length
• D. Decreased power of the cornea

Explanation: Astigmatism occurs when the refracting surface (usually the cornea) has different curvatures in different meridians, creating two focal lines instead of a single point. The cornea accounts for ~90% of astigmatism.

• A. Horizontal meridian is steeper (axis of minus cylinder at 90°)
• B. Vertical meridian is steeper (axis of minus cylinder at 180°) ✓
• C. Oblique meridian is steeper
• D. Both meridians are equally steep

Explanation: In with-the-rule (WTR) astigmatism, the vertical meridian (90°) has greater refracting power. The correcting minus cylinder axis is at 180° (or plus cylinder axis at 90°). WTR is more common in young individuals; against-the-rule (ATR) becomes more common with age.

• A. 180°
• B. 90° ✓
• C. 45°
• D. 135°

Explanation: In ATR astigmatism, the horizontal meridian is the steeper one. The minus cylinder axis is placed at 90° (or plus cylinder at 180°).

• A. Principal meridians at 90° and 180°
• B. Principal meridians between 20-70° or 110-160° ✓
• C. Principal meridians not at right angles to each other
• D. Astigmatism caused by the lens

Explanation: Oblique astigmatism - the principal meridians lie between 20°-70° or 110°-160°. If the meridians are NOT at right angles to each other, it is called "irregular astigmatism."

SECTION 2: Classification of Astigmatism

• A. Behind the retina
• B. In front of the retina
• C. On the retina ✓
• D. One focal line is on retina, one in front

Explanation: In simple myopic astigmatism, one focal line falls in front of the retina and the other falls ON the retina. The Sturm's conoid: circle of least confusion lies between the two focal lines.

• A. Simple myopic astigmatism
• B. Compound hypermetropic astigmatism
• C. Mixed astigmatism
• D. Lenticular astigmatism ✓ (this is a cause, not a "type" in the classification)

Explanation: Regular astigmatism is classified as:

1. Simple myopic / hypermetropic astigmatism
2. Compound myopic / hypermetropic astigmatism
3. Mixed astigmatism (one meridian myopic, other hypermetropic)

• A. Spherical convex lens
• B. Spherical concave lens
• C. Cylindrical lens only
• D. Sphero-cylindrical lens ✓

Explanation: Mixed astigmatism has one focal line in front and one behind the retina. It requires a sphero-cylindrical lens. Can also be written as a cross-cylinder or transposed.

SECTION 3: Irregular Astigmatism

• A. Keratoconus ✓
• B. Cataract
• C. Trauma
• D. Corneal ulcer

Explanation: Keratoconus causes irregular astigmatism because the thinning produces a conical cornea with no regular principal meridians. It is NOT correctable with spectacles but CAN be corrected with rigid contact lenses (hard/RGP). - Kanski's Clinical Ophthalmology, p. 300

• A. Spectacle glasses
• B. Rigid/hard contact lens (RGP) ✓
• C. Toric soft contact lens
• D. Cylindrical spectacle lens

Explanation: Irregular astigmatism (as in keratoconus, corneal scars) cannot be corrected by spectacles or soft contact lenses. Rigid gas-permeable (RGP) contact lenses create a new regular refracting surface by filling irregularities with tear film.

• A. Simple myopic with-the-rule
• B. High irregular against-the-rule astigmatism ✓
• C. Regular compound hypermetropic
• D. Mixed astigmatism

Explanation: Pellucid marginal degeneration causes peripheral corneal thinning in the inferior quadrant, producing high irregular against-the-rule astigmatism. Corneal protrusion occurs above the band of thinning. - Wills Eye Manual

SECTION 4: Sturm's Conoid & Optics

• A. Distance between retina and far point
• B. Distance between the two focal lines in astigmatism ✓
• C. Distance between nodal point and principal focus
• D. Diameter of the circle of least confusion

Explanation: In regular astigmatism, Sturm's conoid is the optical system with two focal lines. The interval of Sturm = distance between the two focal lines. The circle of least confusion lies midway between the two focal lines.

• A. At the anterior focal line
• B. At the posterior focal line
• C. Midway between the two focal lines ✓
• D. At the retina always

• A. Cylindrical lens creating astigmatism ✓
• B. Prism deviation
• C. Pinhole effect
• D. Stenopaic slit

SECTION 5: Correction & Treatment

• A. Detect strabismus
• B. Find the axis of astigmatism ✓
• C. Measure intraocular pressure
• D. Assess accommodation

Explanation: The stenopaic slit is a narrow slit aperture. When oriented along the axis of astigmatism, it neutralizes one meridian and allows subjective refraction. It is used to determine the axis and also to refract patients with nystagmus or irregular astigmatism.

• A. Radial keratotomy
• B. Limbal relaxing incisions / Arcuate keratotomy ✓
• C. PRK
• D. Conductive keratoplasty

Explanation: Arcuate keratotomy (limbal relaxing incisions) involves paired arcuate incisions on opposite sides of the cornea along the steep meridian. This flattens the steep meridian and steepens the flat meridian (coupling effect), reducing astigmatism. - Kanski's Clinical Ophthalmology, p. 300

• A. 3 D
• B. 4 D
• C. 5 D ✓
• D. 6 D

Explanation: PRK/LASEK can correct up to 3 D of astigmatism; LASIK can correct up to 5 D of astigmatism. - Kanski's Clinical Ophthalmology, p. 300

• A. Regular astigmatism during cataract surgery ✓
• B. Irregular astigmatism
• C. Presbyopia
• D. High myopia

Explanation: Toric intraocular implants incorporate an astigmatic correction for regular astigmatism. A key concern is postoperative rotation of the implant away from the desired axis. - Kanski's Clinical Ophthalmology, p. 300

SECTION 6: Lenticular & Index Astigmatism

• A. Corneal astigmatism
• B. Residual astigmatism
• C. Lenticular/index astigmatism ✓
• D. Oblique astigmatism

• A. Astigmatism remaining after cataract surgery
• B. Total astigmatism minus corneal astigmatism (mainly lenticular) ✓
• C. Astigmatism after LASIK
• D. Astigmatism due to vitreous

Explanation: Total astigmatism = corneal astigmatism + lenticular astigmatism. Residual astigmatism = total minus corneal = approximately 0.50 D in most people.

SECTION 7: Pediatric Prescribing & Clinical Points

• A. 0.50 D
• B. 1.00 D
• C. 1.50 D ✓
• D. 2.00 D

Explanation: "A cylinder of 1.50 D or more should probably be prescribed, especially in anisometropia after the age of 18 months." - Kanski's Clinical Ophthalmology, p. 2331

• A. Children and young adults ✓
• B. Elderly
• C. Males only
• D. Patients with keratoconus

Explanation: WTR astigmatism (vertical meridian steeper) is more common in young people. With age, there is a shift to ATR astigmatism (horizontal meridian steeper). This is a classic NEET PG fact.

• A. Simple myopic
• B. Regular with-the-rule
• C. Irregular ✓
• D. Compound hypermetropic

Explanation: Keratoconus - progressive corneal thinning produces a conical cornea with irregular astigmatism that is difficult to correct with spectacles. Incidence: 1 in 2000. Associated with atopy, Down syndrome, Marfan syndrome. - Robbins Pathology

Quick Revision Table

High-Yield Points to Remember

1. Cornea contributes ~90% of total astigmatism
2. Keratoconus = irregular astigmatism, corrected by RGP contact lens
3. Pellucid marginal degeneration = high irregular ATR astigmatism
4. Stenopaic slit finds the axis of astigmatism
5. Interval of Sturm = distance between two focal lines in Sturm's conoid
6. LASIK corrects up to 5 D astigmatism; PRK/LASEK up to 3 D
7. Toric IOL - risk of postoperative rotation
8. Arcuate keratotomy - incisions in the steep meridian
9. Cylinder of 1.50 D threshold for prescribing in children (Kanski)
10. WTR shifts to ATR with increasing age