Astigmatism occurs when parallel rays of light focus at multiple points due to the cornea having unequal curvature in different meridians. It can be classified based on the focus of the principal meridians as simple, compound, or mixed. Regular astigmatism occurs when the principal meridians are perpendicular, and can be with-the-rule, against-the-rule, or oblique. Irregular astigmatism results from corneal scarring or conditions like keratoconus. Astigmatism is typically corrected using cylindrical lenses in glasses or toric contact lenses. The decision to correct depends on the amount and whether it is causing symptoms.

1. Farhana Adnin
B.Optom,4th batch,
Institute of Community Ophthalmolog
University of Chittagong
Astigmatism correction

2. Definition ???
 When parallel rays of light come from infinity and create
multiple focal point with accommodation at rest is called
astigmatism.

3. For example
The image may be focused on the retina in the horizontal
(sagittal )plane,but not on the retina in the vertical plane
 Most Astigmatic cornea have two curves,one is steeper
and another oner a flatter curve

4. OPTICS…
A.Compound
Hyp.Astig
B.Simpl
e
Hyp.
C D E –Mixed Astig
F.Simple
Myop.A
G.Compound
Myop.A

5. Classification…
Based on focus of the principal meridian-
1. Simple astigmatism:
 Simple hyperopic astigmatism
 Simple myopic astigmatism
2.Compound astigmatism:
Compound hyperopic astigmatism
Compound myopic astigmatism
3.Mixed astigmatism

6. Cont…

7. Continue…
Based on axis of the principal meridians-
1.Regular astigmatism:
With the rule astigmatism
Against the rule astigmatism
Oblique astigmatism
2. Irregular astigmatism
Based on severity-
Mild astigmatism : <1 D
Moderate astigmatism : 1.00 to 2.00 D
 Severe astigmatism : 2.00 to 3.00 D
 Extreme astigmatism : > 3.00 D

8. Regular Astigmatism…
When horizontal and vertical meridians are at right angle
to each other.
With the rule astigmatism :The two principal meridian are
at perpendicular to each other but vertical meridian is
more curved than horizontal meridian.
Range-60 to 120 degree

9. Cont…
Against the rule astigmatism : In which the horizontal
meridian is more curved than the vertical meridian.
Range : 0 to 30 degree,
150 to 180 degree.

10. Oblique astigmatism : Where the two principal meridian
are not the horizontal or vertical but these are
perpendicular to one other.
Range : 30 to 60 degree, 120 to 150 degree
For example : If one axis in 45 and another axis in 135
degree

11. Regular astigmatism…
Etiology
1.Corneal - abnormalities of curvature [common]
2. Lenticular- rare. It may be:
i. Curvatural - abnormalities of curvature of lens as seen in
lenticonus.
ii. Positional - tilting or oblique placement of lens ,
subluxation.
iii. iii. Index astigmatism – variable refractive index in
different meridian.
3. Retinal - oblique placement of macula [rare]

12. Cont..
 Eye strain
 Discomfort
 Headache
 Dry eye
 Sensitivity to light
 Blurred vision
 Frequent blinking
 Head tilt
 Half closer of the lid
 Oval or tilt optic disc
 Different power in
different meridian
Symptoms Signs

13. Cont..
Investigations:
 Retinoscopy
 Keratometry
 Autorefractometer
 Astigmatic fan test
 Jackson cross cylinder
 Stenopaeic slit

14. cont…
Management:
Spherocylindrical spectacles
Contact lens
--Soft contact lens
-- Toric -Soft lenses
-Rigid gas permeable lenses
 Refractive surgery

15. Refractive surgeries
 Astigmatic Keratotomy-upto 4-6D
 Photo Astigmatic refractive Keratectomy [PARK]- upto 3D
 LASIK surgery-upto 5-10D

16. Irregular Astigmatism
Defective vision
Distortion of objects
Polyopia
 Irregular pupillary reflex
 Corneal irregularity
 Irregular corneal curvature
Symptoms Signs

17. Etiology :
Corneal –
Scars
Keratoconus
Flap complications
Marginal degenration ,
Lenticular –
Cataract maturation

18. Investigations:
 Placido's disc test reveals distorted circles
 Corneal topography
 Penta cam

19. Treatment :
1.Optical treatment :
RGP contact lenses
Hybrid contact lenses
Scleral lenses
Piggyback lens
2.Corneal Cross-Linking With Riboflavin and Ultraviolet
Irradiation
3.Penetrating Keratoplasty [PKP]
4.Deep Anterior Lamellar Keratoplasty [DALK] etc.

20. Physiological astigmatism
 Diameter of cornea in vertical axis is 11.5mm and in horizontal
meridian is 12mm.
 This means horizontal meridian is flatter than vertical.
 Because diameter is inversely proportional to curvature.
 Occur as lid press on anterior corneal surface.
 Make vertical meridian steeper
 Only small astigmatic error
 Usually 0.12D
 No treatment required

21. Total astigmatism…
Corneal astigmatism: When the cornea has unequal
curvature or dioptric power on the anterior surface.
Internal astigmatism: It occurs due to posterior surface
of cornea & tilting of crystalline lens.
Total astigmatism: The sum of corneal & internal
astigmatism.

22. Residual astigmatism:
The amount of astigmatism that still remains after correction of
a refractive error.
In the case of correction of corneal astigmatism using rigid
contact lens ,lenticular residual astigmatism is exposed.

23. Surgical induced astigmatism…
 Usually following cataract surgery
 Induced by incission or suture
 If without suture ---
Against the rule astigmatism (superior limbal incission)
With the rule astigmatism (temporal limbal incission)
 If with suture ----(Opposite )
With the rule astigmatism (superior limbal incission)
Against the rule astigmatism (temporal limbal incission)

24. Cont…
 Management:
After 1 month of surgery spectacles prescribed.
Others-
Selective removal of sutures:
If more than 2-3 D WTR astigmatism present then after 2
month , suture with the steepest curve must be removed.
Relaxing incisions combined with compression (upto 10D
etc

25. Case study
 MR-910951
 Name: Abdul Barek
 Age- 20 y
 Gender- Male
 C/O- Dimness of vision B/E
 VAR-6/60 |PH 6/9
 VAL-3/60 |PH 6/9
Objective refraction-
OD)-2.50D/-8.50DC @40deg
OS)-9.00D/-12.00DC@170deg
Subjective refraction-
OD)-2.00D/-6.00DC@40....6/18
OS)-8.00D/-8.00DC@170...6/24
No glass prescribed
Patient was given RGP contact lens
OD)-5.00/6.00/9.00...6/9
OS)-5.oo/7.15/9.20....6/9

26. When to prescribe...?
1.Symptomatic patient:
~rarely <-0.75DC uncorrected astigmatism induce
symptom especially @180 degree.
~but induce symptom for <+0.75DC @90 degree or
oblique astigmatism since they tend to guide
accommodation all the time towards the circle of least
confusion.

27. cont....
2.Amblyopia risk:
~If <2DC, need not to be prescribed, as it may interfere
with emmetropization. (<6yrs)
~but in case of oblique <1.25DC after the age of 2 years
should be prescribed.
~Astigmatism that could reduce acuity , especially at near
or creates symptoms need to be prescribed directly.

28. When not to be prescribed...
 1.History of dizziness, disorientation and ear
infections etc.
 2.Small amounts , first time user,
recheck..especially if habitual Rx had always been
spherical.
 3.Highly cylindrical corrections .Check axis and
amount at near. consider under correcting
according to findings

29. 3 strategies for better tolerance...
 1.If changes in astigmatic refraction are >0.50 DC,
consider decreasing cylinder by adjusting sphere.

30.  2.Approach equality in cylindrical powers. Especially
when axis are oblique.

31.  3.When patient reports failure of previous attempts
with astigmatic correction or axis are very different
from the habitual, consider prescribing spherical
equivalent.

32. Key points before prescribing…
Keep axis as symmetrical as possible.
Keep axis as close to main meridians as possible.
Consult sensitive patients not to make significant changes
in frames shape.
Try to keep difference of correction between 2 eyes
within +/- 2.50DC.
More than 6DC should not be prescribed to make
grinding easier.

33. Reference...
 Primary care optometry
 Theory and practice of optics and refraction~
A.K.Khurana
 Essentials of Ophthalmology~ Samar K Basak
 Comprehensive Ophthalmplogy~ A.K.Khurana
 Internet