2d:I[856015,["/_next/static/immutable/chunks/1xzisbplk9czp.js","/_next/static/immutable/chunks/3j2i1faptc_-9.js","/_next/static/immutable/chunks/0fma7nlq6immz.js","/_next/static/immutable/chunks/08tq8rmv423j5.js","/_next/static/immutable/chunks/1chr5wkk3j58k.js","/_next/static/immutable/chunks/37kmmh_zm4dov.js","/_next/static/immutable/chunks/311zvdjfxff-f.js","/_next/static/immutable/chunks/1a_hqhrsle_n_.js"],"default"] 2e:T52f5,

Summary Table

Feature	Detail
Risk Factors	Family history of refractive errors, keratoconus, corneal scarring, post-surgical changes (e.g., after cataract surgery), lid lesions such as chalazion causing mechanical pressure on the cornea
Etiology	Unequal curvature of the cornea (most common) or lens, resulting in multiple focal points rather than a single point of focus on the retina
Patient Presentation	Blurred vision at all distances (both near and far), eye strain, headache after prolonged reading, squinting
Classic Physical Exam	Reduced visual acuity not fully correctable with a simple spherical lens; improvement with pinhole test (rules out retinal pathology); distorted or tilted images on ophthalmoscopy
Key Diagnostic Results	Keratometry reveals unequal corneal curvature; retinoscopy shows a "band" or "streak" reflex instead of a round spot; corneal topography maps the irregular surface
Management	Cylindrical (toric) corrective lenses (glasses or contact lenses); refractive surgery (LASIK, PRK) for definitive correction
Keywords	"Blurred vision at all distances," "cylindrical lens," "two focal lines," "irregular corneal curvature," "fan dial chart"

1. Pathophysiology

The normal cornea is shaped like a perfect sphere, comparable to a basketball, where light rays entering the eye converge to a single focal point on the retina. In astigmatism, the cornea (or less commonly the lens) has unequal curvature along different meridians, resembling the surface of a rugby ball or the back of a spoon. One meridian is steeper than the perpendicular meridian.

Because of this asymmetry, light entering the eye is refracted unequally. Instead of producing a single focal point, the optical system creates two focal lines (Sturm's interval) at different distances from the retina. The space between these two focal lines is called the conoid of Sturm, and the circular cross-section midway between them is the circle of least confusion. The retinal image is never a sharp point but rather an elliptical blur, which is why the patient reports blurred and distorted vision at all distances. This distinguishes astigmatism from myopia (blurred far vision only) and hyperopia (blurred near vision primarily).

The key concept tested is that a spherical lens alone cannot correct astigmatism because it moves both focal lines equally, never collapsing them into a single point. A cylindrical lens is required because it refracts light along only one meridian, allowing the clinician to bring the two focal lines together onto the retina.

Regular astigmatism occurs when the two principal meridians are perpendicular to each other (90 degrees apart). Irregular astigmatism occurs when the meridians are not perpendicular, typically seen in conditions such as keratoconus, corneal scarring, or post-traumatic corneal irregularity. Irregular astigmatism cannot be fully corrected with spectacles and requires rigid gas-permeable (RGP) contact lenses or corneal procedures.

2. Classification and Clinical Manifestation

Type	Description	Focal Points	Clinical Relevance
Simple Myopic	One focal line on the retina, the other in front	One meridian emmetropic, the other myopic	Corrected with a plano-concave cylindrical lens
Simple Hyperopic	One focal line on the retina, the other behind	One meridian emmetropic, the other hyperopic	Corrected with a plano-convex cylindrical lens
Compound Myopic	Both focal lines fall in front of the retina	Both meridians myopic but to different degrees	Corrected with a combined sphero-cylindrical concave lens
Compound Hyperopic	Both focal lines fall behind the retina	Both meridians hyperopic but to different degrees	Corrected with a combined sphero-cylindrical convex lens
Mixed	One focal line in front, the other behind the retina	One meridian myopic, the other hyperopic	Corrected with a cross-cylinder combination

Based on Axis Orientation

Subtype	Steeper Meridian	Association
With-the-rule	Vertical meridian (around 90 degrees)	More common in children and young adults; the vertical cornea is steeper, corrected with a minus cylinder at 180 degrees
Against-the-rule	Horizontal meridian (around 180 degrees)	More common in older adults (lid laxity reduces vertical pressure); corrected with a minus cylinder at 90 degrees
Oblique	Neither at 90 nor 180 degrees (typically 30 to 60 or 120 to 150 degrees)	Less common; same correction principles apply along the identified axis

The clinical pearl here is that aging shifts astigmatism from with-the-rule toward against-the-rule due to changes in eyelid tension on the cornea.

3. Diagnostic Workup

Test	Purpose	Key Findings
Snellen Chart	Screen for reduced visual acuity	Blurred at distance; improvement with pinhole suggests refractive error rather than retinal or optic nerve pathology
Pinhole Test	Distinguish refractive error from organic pathology	Improvement confirms refractive origin; no improvement raises concern for macular or optic nerve disease
Retinoscopy	Objective measurement of refractive error (best initial test for quantifying astigmatism)	A band/streak reflex that moves in different directions along different meridians instead of a uniform round spot; "scissors" reflex suggests irregular astigmatism
Keratometry	Measures corneal curvature in two principal meridians	Unequal readings between meridians confirm corneal astigmatism and quantify the difference
Corneal Topography	Gold standard for mapping the entire corneal surface	Color-coded map showing curvature variation; essential for detecting keratoconus and planning refractive surgery
Autorefraction	Automated objective refraction	Provides a starting point for cylindrical correction; less precise than manual retinoscopy in complex cases
Subjective Refraction (with Jackson Cross-Cylinder)	Final refinement of axis and power	The patient compares two orientations to fine-tune cylindrical correction; this is the confirmatory step for prescribing lenses

The best initial test in a clinical vignette is retinoscopy, which objectively identifies the presence and approximate magnitude of astigmatism by demonstrating a streak reflex whose orientation differs across meridians. A round, uniform reflex would indicate a purely spherical error.

When the vignette describes distorted vision that improves with pinhole but the spherical correction alone is insufficient, the next step is retinoscopy followed by keratometry to determine whether the astigmatism is corneal. For surgical planning or suspected keratoconus, corneal topography is the most accurate and comprehensive test because it maps the entire anterior corneal surface rather than measuring only two points.

The Jackson cross-cylinder test is the standard method during subjective refraction for refining both the axis and power of the cylindrical lens. The examiner flips the cross-cylinder lens, and the patient reports which orientation provides clearer vision. This iterative process isolates the correct cylinder prescription.

An important concept is that irregular astigmatism (from keratoconus, scars, or pterygium) produces an irregular retinoscopic reflex ("scissors" movement) and cannot be adequately characterized by simple keratometry alone, necessitating corneal topography.

4. Management and Treatment

Clinical Scenario	Treatment	Details
Mild regular astigmatism	Cylindrical spectacle lenses	Minus cylinder convention is standard; correct axis precisely
Moderate to high regular astigmatism	Toric contact lenses	Soft toric lenses for comfort; must maintain rotational stability on the eye
Irregular astigmatism (keratoconus, scarring)	Rigid gas-permeable (RGP) contact lenses	The tear film between the rigid lens and irregular cornea creates a smooth refracting surface; first-line for irregular astigmatism
Refractive surgery candidates	LASIK or PRK	Laser ablation reshapes the cornea to equalize meridional curvature; requires stable refraction and adequate corneal thickness
Advanced keratoconus or post-scarring	Corneal collagen cross-linking (CXL), intracorneal ring segments (ICRS), or keratoplasty	CXL stabilizes progressive keratoconus; ICRS flattens the cone; penetrating or lamellar keratoplasty for severe cases

Spectacle correction remains the first-line treatment. The prescription is written with a spherical component (if any coexisting myopia or hyperopia) and a cylindrical component specifying both power and axis. For example, $-2.00 / -1.50 \times 180$ indicates 2 diopters of myopic spherical correction with 1.5 diopters of cylinder at axis 180 degrees.

For patients who cannot tolerate glasses or have high astigmatism (typically greater than 2 to 3 diopters), toric contact lenses provide better optical correction and peripheral vision. These lenses incorporate stabilization mechanisms (prism ballast, thin zones, or truncation) to prevent rotation on the eye, which would shift the cylindrical axis and degrade vision.

In irregular astigmatism, spectacles and soft contact lenses cannot adequately correct the optical distortion. RGP lenses are the treatment of choice because the rigid lens surface overrides the corneal irregularity, while the tear film fills the gap between the lens and cornea. This is the classic tested concept: when a vignette describes a patient with keratoconus whose vision does not improve with spectacles, the answer is RGP contact lenses.

Refractive surgery (LASIK, PRK) is appropriate for patients with stable regular astigmatism who wish to reduce dependence on corrective lenses. Contraindications include thin corneas (risk of post-LASIK ectasia), unstable refraction, keratoconus, pregnancy (transient refractive changes), and severe dry eye. PRK is preferred over LASIK in patients with thinner corneas because it does not create a flap.

For progressive keratoconus, corneal collagen cross-linking with riboflavin and UV-A light strengthens the corneal stroma and halts progression. This does not reverse existing ectasia but prevents worsening. In advanced cases where contact lenses are no longer effective and corneal scarring has developed, keratoplasty (corneal transplantation) becomes necessary.

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Looks Similar	Key Discriminator
Myopia	Also causes blurred vision and improves with pinhole	Myopia causes blurred distance vision only; near vision is preserved. Astigmatism causes distortion at all distances. Retinoscopy shows a round reflex in pure myopia versus a streak in astigmatism
Hyperopia	Also causes eye strain and headache, especially with near work	Hyperopia primarily impairs near vision (or is compensated by accommodation in young patients). A convex spherical lens fully corrects hyperopia; astigmatism requires a cylindrical component
Presbyopia	Causes difficulty with near vision and reading strain	Onset after age 40 due to loss of lens accommodation. Distance vision remains intact. Corrected with reading glasses (convex spherical), not cylindrical lenses
Keratoconus	Causes progressive astigmatism and blurred vision	Keratoconus produces irregular astigmatism with progressive worsening, Munson sign (V-shaped indentation of the lower lid on downgaze), Vogt striae, Fleischer ring, and scissoring on retinoscopy. Standard spectacles do not adequately correct it
Corneal ulcer or scar	Can induce irregular astigmatism	History of trauma, infection, or contact lens overwear. Slit lamp reveals the opacity or ulcer. The astigmatism is acquired rather than longstanding
Lenticular astigmatism	Also causes astigmatic refractive error	Keratometry values are normal (cornea is spherical), indicating the astigmatism arises from the lens rather than the cornea. Less common and not correctable with RGP lenses

6. Traps and High-Yield Pearls

The most common way students lose points on astigmatism questions is by failing to recognize that blurred vision at all distances is the hallmark presentation. When a vignette describes a patient with visual complaints that persist for both near and far objects and a spherical lens trial does not fully resolve the problem, the test-writer is guiding you toward astigmatism. Students who see "blurred distance vision" often default to myopia without noticing the additional mention of near vision difficulty or image distortion.

A second common trap involves irregular astigmatism. When the vignette describes a young patient with progressive visual deterioration, frequent prescription changes, and a scissoring reflex on retinoscopy, the answer is keratoconus, and the treatment is RGP contact lenses, not spectacles and not soft toric lenses. Students who select "new glasses" will miss this because spectacles cannot correct the irregular corneal surface.

Another tested concept is the distinction between with-the-rule and against-the-rule astigmatism in the context of age. Vignettes featuring elderly patients with new-onset or worsening astigmatism are often testing the concept of against-the-rule shift with aging.

Finally, remember the contraindications to LASIK. A vignette describing a patient with astigmatism and thin corneas, unstable refraction, or keratoconus who asks about laser correction is testing whether you know to recommend PRK (if corneal thickness is borderline) or to advise against refractive surgery entirely (if keratoconus is present). The core competency being tested across all these scenarios is the ability to match the type of astigmatism (regular versus irregular) and the clinical context to the correct optical or surgical management.

1e:["$","$L2d",null,{"article":{"id":"0ca4d4b7-0867-4d3a-8618-af9a0488bd69","title":"Astigmatisme","content":"$2e","category":"Oftalmologi","created_at":"2026-05-13T10:21:04.43568+00:00","status":"published","subcategory":null},"questionCount":4,"sections":[{"id":"section-pathophysiology","num":"01","title":"Pathophysiology"},{"id":"section-classification-and-clinical-manifestation","num":"02","title":"Classification and Clinical Manifestation"},{"id":"section-diagnostic-workup","num":"03","title":"Diagnostic Workup"},{"id":"section-management-and-treatment","num":"04","title":"Management and Treatment"},{"id":"section-differential-diagnosis-and-distractors","num":"05","title":"Differential Diagnosis and Distractors"},{"id":"section-traps-and-high-yield-pearls","num":"06","title":"Traps and High-Yield Pearls"}],"hasSummaryTable":true}]