Astigmatism is a refractive condition where the eye's refractive power varies in different meridians, causing blurred vision. It occurs when the cornea or lens is irregularly curved or positioned. Common causes are corneal abnormalities, lenticular conditions, or retinal placement issues. Symptoms include blurred distance and near vision. Diagnosis involves visual acuity tests, autorefraction, keratometry, and retinoscopy. Treatment options are spectacle lenses, toric contact lenses, and refractive surgery such as PRK or LASIK.

1. Dr. Atul Kumar Anand
Senior Resident
AIIMS Patna

3. A refractive condition in
which a variation of
power exists in the
different meridians of the
eye.

4. Astigmatism by definition is a condition where
the parallel beam of light rays incident on the
cornea after refraction are not focused to
form a point image near or on the retina

5. Irregular curvature or RI in the anterior
surface of cornea
Irregular curvature or RI and also the
position of lens/IOL
The refracting power is not uniform in all
meridians of both lens or cornea

6. Based on axis of the principal
meridians
Regular astigmatism – principal meridians
are perpendicular
• With-the-rule astigmatism
• Against-the-rule astigmatism
• Oblique astigmatism
Irregular astigmatism - principal meridians
are not perpendicular

7.  Correctable by cylindrical lenses
Etiology :
1. Corneal - abnormalities of curvature [common]
2. Lenticular is rare. It may be:
i. Curvatural - abnormalities of curvature of
lens as seen in lenticonus.
ii. Positional - tilting or oblique placement of
lens , subluxation.
3. Retinal - oblique placement of macula [rare]

8. Based on focus of the principal
meridians
Simple astigmatism
• Simple hyperopic astigmatism
• Simple myopic astigmatism
Compound astigmatism
• Compound hyperopic astigmatism
• Compound myopic astigmatism
Mixed astigmatism

11. •Distorted vision at
distance and near
•Letter confusion
•Asthenopia or
ocular fatigue
•Headaches
•Squinting

12. • Symptoms :
Blurring of vision
Asthenopic symptoms
Tilting of head
Squinting

13. Visual acuity tests – distance and near
Autorefraction
Keratometry
Retinoscopy
Monocular subjective refraction

14.  Spectacles
Cylindrical lenses and spherocylindrical lenses in
spectacles
 Contact lens
Toric soft contact lenses
 rigid gas permeable contact lenses
 Refractive surgery
Photorefractive keratectomy (PRK)
Laser in-situ keratomileusis (LASIK)

15. Astigmatic fan
Jackson’s cross cylinder
Stenopic slit

16. • Etiology :
Corneal -[ Scars , Keratoconus
flap complications,
marginal degenration ]
Lenticular -[Cataract maturation]
Retinal-[scarring of macula,
tumours of retina,choroid]

17. Symptoms :
Defective vision
Distorsion of objects
Polyopia
Investigations:
- Placido's disc test reveals distorted
circles
- Computerized corneal topography

19.  Optical treatment :
- RGP contact lenses
-Hybrid contact lenses
-Scleral lenses
 Surgical treatment:
- penetrating keratoplasty

20.  The amount of astigmatism that still
remains after correction of a refractive
error.

21. Difference in refractive power between 2
eyes
refractive correction often leads to different
image sizes on the 2 retinas( aniseikonia)
aniseikonia depend on degree of refractive
anomaly and type of correction

22. Glasses : magnified or minified 2% per 1 D
Contact lens : change less than glasses
Tolerate aniseikonia ~ 5-8%
Treatment
• anisometropia > 4 D-->contact lens
• unilateral aphakia-->contact lens or
intraocular lens