concise description of aniseikonia which is a condition wherein the images projected to the visual cortex from the two retinae are abnormally unequal in size and /or shape

1. ANISEIKONIA
 A condition wherein the images projected to the
visual cortex from the two retinae are abnormally
unequal in size and/or shape.
 Up to 5% - well tolerated.

2. Symptoms
• 1. Asthenopia, i.e., eyeache, browache and tiredness
• of eyes.
• 2. Diplopia due to difficult binocular vision when
• the difference in images of two eyes is more than
• 5 percent
• 3. Difficulty in depth perception.

3. Etiological types
Optical aniseikonia
• may occur due to
either inherent or
acquired
anisometropia of
high degree.
Retinal aniseikonia
• may develop due
to: displacement
of retinal
elements towards
the nodal point in
one eye due to
stretching or
oedema of the
retina.
Cortical aniseikonia
• implies
asymmetrical
simultaneous
perception inspite
of equal size of
images formed on
the two retinae.

4. Clinical types
a) Spherical - magnified or
minified equally in both
meridia
b) Cylindrical - magnified or
minified symmetrically in one
meridian .
a) Prismatic - image difference
increases progressively in one
direction
b) Pincushion - image distortion
increases progressively in both
directions, as seen with high plus
correction in aphakia
c) Barrel distortion - image distortion
decreases progressively in both
directions, as seen with high minus
correction
d) Oblique distortion- size of image is
same, but oblique distortion of
shape
• 1. Symmetrical aniseikonia • 2. Asymetrical aniseikonia

5. Treatment
• 1. Optical aniseikonia may be corrected by
• aniseikonic glasses, contact lenses or intraocular
• lenses depending upon the situation.
• 2. For retinal aniseikonia treat the cause.
• 3. Cortical aniseikonia is very difficult to treat.

6. APHAKIA
‘Absence of crystalline lens’ from the eye
Optical point of view – condition in which lens is absent from
the pupillary area
Produces high degree hypermetropia

8. Causes
1. Congenital absence of lens
2. Surgical aphakia
3. Aphakia due to absorption of lens matter
4. Trauma extrusion of lens
5. Posterior dislocation of lens

9. Optical changes in the eye after
removal of crystalline lens
• High degree hypermetropia
• Total power of eye is reduced from +60D to about +44D
• Anterior focal point becomes 23.2 mm in front of the cornea ( N : 15.7 mm )
• Posterior focal point is about 7mm behind the eyeball i.e 31mm behind the cornea
• Accommodation is lost completely

10. Clinical features
SYMPTOMS –
• Defective vision : for both far and near
• Erythropsia and cyanopsia
SIGNS –
• Limbal scar
• Anterior chamber deeper than normal
• Iridodonesis
• Pupil is jet black in colour
• Purkinje image test shows only two images
• Fundus examination shows hypermetrophic small
disc
• Retinoscopy and autorefractometry reveals high
hypermetropia

11. Treatment
 Spectacles –
 +10D with cylindrical lenses for surgically induced astigmatism in previously emmetropic
patients
 An addition of +3 to +4 D is required for near vision to compensate for loss of accommodation.
 Contact lens
 IOL Implantation
o Primary IOL implantation- during cataract surgery
o Secondary IOL implantation- already aphakic patients
 Refractive corneal surgery
o Keratophakia, Epikeratophakia, Hyperopic LASIK

12.  Keratophakia. In this
procedure a lenticule
prepared from the donor
cornea is placed between the
lamellae of patient's cornea.
 Epikeratophakia. In this
procedure, the lenticule
prepared from the donor
cornea is stitched over the
surface of cornea after
removing the epithelium.
 Hyperopic Lasik

13. Anisometropia
Condition where total refraction of two eyes is
unequal

14. degree of
anisometropia
difference in size of
two retinal images
1 D 2 % No concern
2.5 D 5 % Well tolerated
2.5 D to 4 D can be tolerated
depending upon the
individual sensitivity
> 4 D not tolerated
Matter of concern

15. ETIOLOGY –
1.Congenital and developmental anisometropia
- due to differential growth of eyeballs
2.Acquired anisometropia
- asymmetric age change
- removal of cataractous lens
- implantation of IOL of wrong power

16. CLINICAL TYPES –
1.Simple anisometropia
- Simple myopic anisometropia
- Simple hypermetropic anisometropia
2. Compound anisometropia
- Compound myopic anisometropia
- Compound hypermetropic anisometropia
3.Mixed anisometropia / antimetropia
4.Simple astigmatic anisometropia
5.Compound astigmatic anisometropia

17. STATUS OF VISION IN ANISOMETROPIA –
1.Small degree anisometropia – Binocular vision
2.When refractive error in one eye is of high degree –
Uniocular vision
3.When one eye is hypermetropic and the other is
myopic – Alternate vision
DIAGNOSIS –
• Retinoscopic examination
• Autorefractometry

18. TREATMENT –
1.Spectacles
2.Contact lenses
3.IOL implantation
4.Refractive corneal surgery
5.Phakic refractive lenses ( PRL )
6.Refractive lens exchange ( RLE )

20. Astigmatism
• Type of refractive error wherein the refraction varies in
the different meridian.
• Consequently, the rays of light entering in the eye cannot
converge to a point focus but form focal lines

21. Regular
BASED ON
ETIOLOGY
1. Corneal
astigmatism
2. Lenticular
astigmatism
i. Curvatural
Eg.lenticonus
ii. Positional
Eg. subluxation.
iii. Index.
3. Retinal
astigmatism
Depending upon
the axis and the
angle between the
two principal
meridia
1. With-the-rule
astigmatism
2. Against-the-rule
astigmatism
3. Oblique
astigmatism
4. Bioblique
astigmatism
Depending upon
the position of the
two focal lines in
relation to retina
Simple
astigmatism,
Compound
astigmatism
Mixed astigmatism

22. • Symptoms
Defective vision;
blurring of objects;
(iii) depending upon the type and degree of
astigmatism, objects may
appear proportionately elongated; and
(iv) asthenopic symptoms, which are marked
especially in small
amount of astigmatism, consist of a dull ache in the
eyes, headache, early tiredness of eyes and
sometimes nausea and even drowsiness.
• Signs
• 1. Different power in two meridia is revealed on
• retinoscopy or autorefractometry.
• 2. Oval or tilted optic disc may be seen on
• ophthalmoscopy in patients with high degree of
• astigmatism.
• 3. Head tilt. The astigmatic patients may (very
• exceptionally) develop a torticollis in an
attempt
• to bring their axes nearer to the horizontal or
• vertical meridians.
• 4. Half closure of the lid. Like myopes, the
astigmatic
• patients may half shut the eyes to achieve the
• greater clarity of stenopaeic vision.

23. Treatment
• 1. Optical treatment
• i. Spectacles with full correction of cylindrical power and appropriate axis should be used for
distance and near vision.
• ii. Contact lenses. Rigid contact lenses may correct upto 2-3 of regular astigmatism, while
soft contact lenses can correct only little astigmatism. For higher degrees of astigmatism toric
contact lenses are needed. In order to maintain the correct axis of toric lenses, ballasting or
truncation is required.
• 2. Surgical correction

24. IRREGULAR ASTIGMATISM
• It is characterized by an irregular change of refractive power in different meridia. There
are multiple meridian which admit no geometrical analysis.
• Etiological types
• 1. Curvatural irregular astigmatism is found in patients with extensive corneal scars or
keratoconus.
• 2. Index irregular astigmatism due to variable refractive index in different parts of the
crystalline lens may occur rarely during maturation of cataract.
• Symptoms of irregular astigmatism include:
• _ Defective vision,
• _ Distortion of objects and
• _ Polyopia.

25. • Investigations
• 1. Placido's disc test reveales distorted circles
• 2. Photokerotoscopy and computerized corneal topography give photographic record of
irregular corneal curvature.
• Treatment
1. Optical treatment - contact lens
2. Phototherapeutic keratectomy (PTK)
3. Surgical treatment is indicated in extensivecorneal and consists of penetrating keratoplasty.

26. Refractive surgery for astigmatism
• Refractive surgical techniques employed for myopia can be adapted to correct
astigmatism alone or simultaneously with myopia as follows:
• 1. Astigmatic keratotomy (AK) refers to makingtransverse cuts in the mid periphery of
the steep corneal meridian
• 2. Photo-astigmatic refractive keratotomy (PARK)
• 3. LASIK to correctastigmatism upto 5D.
• Management of post-keratoplasty astigmatism
• 1. Selective removal of sutures in steep meridians