Astigmatism, anisometropia, anisekonia.

1. ASTIGMATISM, ANISOMETROPIA
AND ANISOKONIA
PRESENTOR- Dr Vishy Srivastava
MODERATOR- Dr Alka Jasrasaria

2. CONTENTS
1. WHAT IS ASTIGMATISM?
2. INCIDENCE
3. OPTICS
4. ETIOLOGY
5. CLASSIFICATION
6. SIGNS AND SYMPTOMS
7. DIAGNOSIS
8. TREATMENT

3. ASTIGMATISM
- Refractive error
- Difference in degree of refraction in different meridians
- Image may be clearly focused on the retina in the horizontal (sagittal) plane,
but not in the vertical (tangential) plane.

4. Most Astigmatic Corneas have 2 curves, steeper and flatter curves
Light focus on more than one point in eye
Cause blurring of vision

5. INCIDENCE
About 60% cases of refractive errors have astigmatism which needs to be corrected.
Occurs with equal frequency in males and females.
Approximate distribution according to degree of astigmatism is:
0.25-0.5 D - 50%
0.75-1.0 D - 25%
1.00-4.00D - 24%
>4.00 - 1.0%
The most common type is compound myopic followed by compound hyperopic, mixed,
simple myopic & simple hyperopic.
One study reports as:
With the rule -38%
Against the rule -30%
Oblique -32%

6. OPTICS
- Rays of light from one sector fall on one point & rays from another
sector fall on another point i.e point focus not formed on retina
Configuration of rays refracted through astigmatic surface(toric
surface) is called strums conoid
Two focal points formed seperated by focal interval called interval
for strum
Length of focal interval forms the measure of degree of astigmatism
Reducing these two foci will lead to correction of astigmatism

7. Axis Meridian
Horizontal
Focal Line
Vertical Focal
Line
Circle of Least
Confusion
Power Meridian
Object
Source
A
B D
C
Interval
of
Sturm

8. ETIOLOGY
TYPES
CORNEAL
ASTIGMATISM
LENTICULAR
ASTIGMATISM
RETINAL
ASTIGMATISM
- D/t abnormalities of
curvature
- Most common type
- E.g Keratoconus,
Chalazion,Pterygium,
mild corneal opacities
Rare
Curvatural
Eg Lenticonus
Positional
Eg Tilting
or
subluxation
of lens
Index eg
Catract/
Nuclear
sclerosis/
Diabetic
catract
Oblique placement
of macula

9. SEVERITY OF ASTIGMATISM
Mild : <1.0D
Moderate : 1.0 – 2.0D
Severe : 2.0 – 3.0D
Extremely severe : >3.0D

10. CLASSIFICATION
ASTIGMATISM
PHYSIOLOGICAL PATHOLOGICAL
REGULAR IRREGULAR
SIMPLE COMPOUND MIXED
-MYOPIC -MYPOIC
-HYPEROPIC -HYPEROPIC

11. BASED ON SYMMETRY
CORNEAL ASTIGMATISM LENTICULAR ASTIGMATISM
D/t Irregularly shaped cornea D/t Irregularly shaped Lens
BASED ON AXIS
REGULAR OBLIQUE BIOBLIQUE IRREGULAR
WITH THE RULE AGAINST THE RULE

12. REGULAR ASTIGMATISM
- If there is different refraction by the eye in two meridia at right angles
to each other.
- Pressure of lids on the corneal surface
- Horizontal curvature of cornea is flatter than vertical
- This is physiological
- Corrected by spectacles
- It is with the rule.

13. WITH THE RULE(DIRECT ASTIGMATISM)
- Principal meridia is right angle to each other.
- Vertical more curved than horizontal.
- T/t – Concave in horizontal and convex in vertical axis.
- Vertical meridian is rendered 0.25 D more convex than horizontal by
the pressure of fleshy upper eyelid
AGAINST THE RULE(INDIRECT ASTIGMATISM)
- Horizontal more curved than vertical.
- T/t – Convex in horizontal axis and concave in vertical axis.
- Associated with old age.

14. OBLIQUE ASTIGMATISM
- Principle meridia are not horizontal or vertical but are at right
angle to each other (45 & 135).
- Usually symmetrical in both eyes (cylinder required at 30 in both
eyes).
- Or complimentary (cylinder required at 30 in one eye and 150 in
other).

15. BIOBLIQUE ASTIGMATISM
The two principle meridia are not at right angle to each other.
e.g. one may be at 30 & other at 100.
IRREGULAR ASTIGMATISM
- Irregular change of refractive power in different meridia
- Multiple meridia which admit no geometrical analysis
- Cannot be corrected by spectacles
- Occurs due to corneal scars, during maturation of cataract, etc

16. BASED ON FOCUS OF PRINCIPAL MERIDIA
SIMPLE COMPOUND MIXED
SIPMLE SIMPLE
HYPEROPIC MYOPIC COMPLUND COMPOUND
HYPEROPIC MYOPIC

17. SIMPLE ASTIGMATISM
- One of the foci falls on retina & other focus falls in front or behind
retina
- This leads to one meridian being emmetropic & other being myopic i.e one
focus on the retina and other in front the retina or Hyperopic i.e one focus on
the retina and other behind the retina so called as simple myopic astigmatism
& simple hyperopic astigmatism respectively.

18. It can be with-the-rule or against-the-rule.
-2 D cyl at 90 is example of simple myopic astigmatism.
+2 D cyl at 90 is example of simple hyperopic astigmatism.

19. COMPOUND ASTIGMATISM
- Neither two foci fall on the retina.
- The condition is known as compound hyperopic if both foci are
at back of retina.
- +4DS with +2DC at 90 is example of compound hyperopic
astigmatism.

20. - The condition is known as compound myopic if both foci are at front
of retina.
-4 DS with -2DC at 90 is example of compound myopic astigmatism

21. MIXED ASTIGMATISM
One of the two foci lies at back while other at front of the retina.
It can be with-the-rule or against-the-rule.
-4 DS with +2DC at 90 is an example of mixed astigmatism.
If cyl power is less than spherical power, then it is not mixed but
compound astigmatism.

22. RESIDUAL ASTIGMATISM
- Largest element of astigmatism is due to anterior corneal surface,
while other component like Posterior corneal surface, lens and
refractive indices constitute residual astigmatism.
- RESIDUAL ASTIGMATISM = TOTAL – CORNEAL ASTIGMATISM

23. SIGNS AND SYMPTOMS
1.BLURRING OF VISON
Transient BOV in low astigmatism
Relieved by closing/Rubbing eyes
Circles elongate to oval, point of light appears to be tailed off
2.ASTHENOPIC SYMPTOMS
More marked in low astigmatism and severe in Hyperopic Astigmatism
Tiredness of eyes
Headache
Dizziness, Fatigue, Irritability
3. TILTING OF HEAD
In high oblique Astigmatism

24. 4.HALF CLOSURE OF LIDS
In high Astigmatism To make a stenopaic slit and cutting out the rays from
one meridian.
5.READING MATERIAL HELD TOO CLOSE
Achieve blur but large image just like myope.
6.BURNING AND ITCHING SENSATION
May be seen in low astigmatism.

25. DIAGNOSIS
VA with and without correction monocularly
Pinhole VA
Retinoscopy
Keratometry– For corneal curvature
Keratoscopy with placido’s disc
Computerised corneal topography/ videograph – For determining corneal curvature
Subjective verification:
Jackson cross cylinder – For Power and Axis
Astigmatic fan & block – Fogging technique using astigmatic fan test.
Trial & error technique (axis then power)
Maddox V
Stenopaeic slit

26. JACKSON CROSS CYLINDER
- Combination of equal strength but opposite
Axis placed at right angle to each other
DISCOVERING ASTIGMATISM
-Cross cylinder placed at 900 and 1800
-If preferred flip found, a cylinder is added with axis
parallel to respective plus or minus axis until two flip
choices match
REFINEMENT OF AXIS
- 0.50D Cross cylinder placed with its handle parallel to
axis and patient asked to tell any changes in VA
-If no difference- Correct axis placed
-If VA attained in one position, “plus” correcting
cylinder rotated in the direction of plus component
REFINEMENT OF CYLINDER POWER
-0.25D cross cylinder placed with axis parallel to axis of
cylinder.
-In first position, cylindrical correction enhanced by
0.25D and in 2nd diminished by same amount
-If VA not improved- correct power of cylinder

27. ASTIGMATIC DIAL WITH FOGGING
OBTAIN BCVA WITH SPHERE & OTHER EYE OCCLUDED
FOG THE EYE BY + SPHERE TO FOCUS ALL MERIDIA
ANTERIOR TO RETINA
PATIENT ASKED TO LOOK AT ASTIGMATIC DIAL AND
IDENTIFY DARKEST AND SHARPEST LINE
ADD MINUS CYLINDER OF PROGRESSIVELY
INCREASING POWER WITH AXIS PERPENDICULAR TO
DARKEST AND SHARPEST LINE TILL ALL LINES ARE
EQUAL
THIS CAUSES VERTICAL FOCAL LINES TO MOVE BACK
TO THE POSITION TO HORIZONTAL FOCAL LINES i.e
INTERVAL OF STRUM IS COLLAPSED
- SWITCH TO DISTANCE VISION CHART AND REDUCE
PLUS SPHERE TILL PATIENT ACHIEVE MAXIMUM
CLARITY

28. ATIGMATIC FAN TEST

29. STENOPAIC SLIT

30. TREATMENT
1. SPECTACLES
Cylindrical lens used
Combination of Spherical and Cylindrical used to correct spherical with
astigmatic error
2. CONTACT LENSES
Soft
Hard
Rigid gas permeable
Hybrid (hard center & soft periphery, used in keratoconus)

31. Depending upon the degree of astigmatism:
Spherical
Toric
Bitoric
3. LASER AND REFRACTIVE SURGERIES
Photorefractive keratectomy PRK
Relaxing incisions (transverse & arcuate keratotomy)
Wedge resection
Compression sutures
Continuous sutures ( astigmatism low)
Interrupted sutures (astigmatism high)
Orthokeratology (hard lens)
Keratoplasty (keratoconus)

32. ANISOMETROPIA
• Condition in which the two eyes have unequal refractive power.
• Difference of 1 D in two eyes - 2 % difference in size of the two retinal
images
• 5% size difference / 2.5 D - Well tolerated .
• 2.5 – 4 D - Individual sensitivity
• >4 D - not tolerated

33. ETIOLOGY
CONGENITAL
- D/t differential
growth of the
eyeballs.
ACQUIRED
- D/t uniocular aphakia after removal
of crystalline lens or due to
implantation of IOL of wrong power.
CLASSIFICATION
ABSOLUTE RELATIVE
- The refractive power of two - Total refraction of the two eyes can be equal,
eyes is unequal. but the axial length may be different
- This lead to clear retinal image but a
difference in the size of the retinal images

34. TYPES OF ANISOMETROPIA
• Simple
• Compound
• Mixed
• Simple astigmatic anisometropia
• Compound astigmatic anisometropia
• Mixed astigmatic anisometropia

35. 1. SIMPLE ANISOMETROPIA
One eye Myopic and other either myopic(Simple Myopic) or a
Hypermetropic (Simple Hypermetropic)

36. 2. COMPOUND ANISOMETROPIA
Both eyes are either hypermetropic or myopic , but one eye is having
higher refractive error than the other
3. MIXED ANISOMETROPIA
In this , one eye is myopic and the other is hypermetropic. This is also
called antimetropia
4. SIMPLE ASTIGMATIC ANISOMETROPIA
When one eye is normal and the other has either simple myopic or
hypermetropic astigmatism.

37. 5. COMPOUND ASTIGMATIC ANISOMETROPIA
When the both eyes are astigmatic but of unequal degree.
Status of vision in anisometropia
Three possibilities are there :
1. Binocular single vision - In small degree of anisometropia.
2. Uniocular vision - When refractive error in one eye is of
high degree.
3. Alternate vision - When one eye is hypermetropic and
other myopic , then hypermetropic eye is used for distant
vision and myopic for near.

38. 1.Spectacles.
The corrective spectacles can be tolerated up to maximum difference of
4D.After that diplopia may occurs.
2.Contact lenses
for higher degrees of anisometropia .
3.IOL implantation
for uniocular aphakia.
4.Refractive corneal surgery
for unilateral high myopia , astigmatism and hypermetropia.
TREATMENT

39. ANISOKONIA
Anomalies of binocular vision.
Ocular images are unequal in size or shape or both .
Its importance lies in case of eye strain which is difficult to assess .
ETIOLOGY
OPTICAL ANISOKONIA RETINAL ANISOKONIA CORTICAL ANISOKONIA
-Inherited/Acquired Displacement of retinal image Assymetrical simultaeous
-Anisokonia of towards nodal point perception in spite of equal
higher degree size of two images.

40. CLINICAL TYPES
• Spherical : Image may be magnified or minified equally in both meridia.
• Cylindrical : Image is magnified of minified symmetrical in one meridia.
• Asymmetrical
• Prismatic : Image difference increases progressively in one direction
• Pincushion : Image distortion increases progressively in both direction as
seen with high plus correction in aphakia.
• Barrel : Image distortion decreases progressively in both direction as seen
in high minus lenses.
• Oblique : Image size remain the same but there occurs oblique distortion
of shape.

41. SYMPTOMS
• Asthenopic symptoms : Occurs when the difference in image size of the
two images between 0.75 to 5%
• Headache , difficulty in reading, photophobia, difficulty in fixation,
vertigo
• Disturbance of binocular vision.
• Diplopia occur only if the difference exceeds 5%.
• Disturbance in the depth perception and spatial disorientation.
• Suppression of one eye

42. TREATMENT
• Optical < IOL in Aphakia.
contact lenses.
Refractive surgery.
• Retinal Aniseikonia :
corrected by treating the causative disease.
• Cortical Aniseikonia :
Difficult to treat .

43. THANK YOU