OPTICS

1. Anisometropia
Aniseikonia
Aphakia
Pseudophakia
MEDICOACH INTERNATIONAL ACADEMY

2. Anisometropia
 It is a situation in which refractive status of the two eyes are different, i.e.
Unequal.
 If the refractive power is equal in two eyes then it is termed as isometropia
However, an insignificant difference in refractive status of the eyes is quite
common.
AETIOLOGY
A.Hereditary–It is due to congenital cataract, congenital glaucoma, etc.
B. Acquired–It is due to surgical or nonsurgical trauma, unilateral aphakia
and inequality in the rate of refractive changes in both eyes.

3. CLASSIFICATION
I. Based on refractive error
 A. Isoanisometropia–Here refractive status of both the eyes are either
hypermetropic or myopic.
 B. Antimetropia–Here refractive status of one eye is myopia and the other
is hypermetropia.
II. Based on dioptric difference–
Patients symptoms vary significantly with the degree of dioptric difference
between the two eyes
a. Low = 0 to 2.50D
b. High = 2.50D to 6.00D
c. Very high = > 6.00D

4. Clinical types
 Simple anisometropia
 Compound anisometropia
 Mixed anisometropia
 Simple astigmatic anisometropia
 Compound astigmatic anisometropia
 Mixed astigmatic anisometropia

5. OPTICAL PROBLEMS/DIFFICULTIES OF ANISOMETROPIA
 A. Binocular vision: > 2.50D of difference in dioptric strength between the
two eyes leads to eye strain due to effort of fusion. Binocular vision is not
possible with spectacle correction if the anisometropia is > 4.00D.
 B. Amblyopia: Often a difference of > 2.00D in hypermetropic patient is
sufficient to induce amblyopia in the more hypermetropic eye. However,
in myopic patients with anisometropia amblyopia is less likely to develop
unless the difference is very significant.
 C. Squinting: Convergent squint in childhood and divergent squint in
adults.
 D. Diplopia: It develops due to difference in image size of > 8%.

6. TREATMENT
 a.Spectacles
 b. Contact lenses
 c.LASIK
 d. Iseikonic lenses
 e. If the patient is amblyopic (anisometropic
amblyopia)–treatment of amblyopia.

7. Aniseikonia
 It is an anomaly of binocular vision in which the ocular images are
unequal in size or shape or both.
 Up to 5 percentage aniseikonia can be well tolerated.
Aetiology
1.Optical aniseikonia –due to inherent or acquired
anisometropia of high degree
2.Retinal aniseikonia may develop due to
 Displacement of retinal elememnts in one eye
 Stretching or oedema of the retina
3.Cortical aniseikonia due to symmetrical simultaneous
perception in spite of equal size of images formed on the two
retina

8. Symptoms
 Asthenopic symptoms
 Disturbances of binocular vision
 Spatial disorientations or disturbance s in depth
perception.

9. Treatment
 Optical aniseikonia can be corrected by
1. IOL implantation: best for unilateral aphakia
2. Contact Lenses: better choice than spectacles for correcting
anisometropic aniseikonia.
3. Aniseikonic spectacles: are difficult to make and expensive .But very
effective in relieving the symptoms,and are sparingly used
 Retinal aniseikonia:
corrected by treating the causative disease
 Cortical aniseikonia:
very difficult to treat

10. APHAKIA
 Aphakia means absence of the crystalline lens in it’s normal
anatomical position.
 SYMPTOMS
 a. Blurring of vision for both distance and near
 b. History of cataract operation or injury
 c. Patient may wear very thick convex glass.

11.  SIGNS
If extracapsular (ECCE)/intracapsular (ICCE) cataract extraction is
done:
• Vision is finger counting at few feet without glasses.
• Upper limbus—Presence of linear scar with or without sutures (10’0’
nylon—Usually interrupted/continuous) may be seen.
• Anterior chamber depth–Deep.
• Iridodonesis, i.e. tremulousness of iris due to lack of support.
• Pupil–Jetblack due to loss of IIIrd and IVth Purkinje image (in ICCE)
and IIIrd image (in ECCE).
• Ophthalmoscopy–The optic disc is very small.

12. Treatment
 Spectacles
 Spectacles are usually advised after 6 weeks of
surgery. The time is required for complete wound
healing and stabilisation of refractive error
particularly astigmatism.
 Optical disadvantages of aphakic glasses:
 i. Image magnification is 25–30%. So, in uniocular aphakia
binocular vision is not possible due to aniseikonia. Hence,
to avoid diplopia (where phakic eye vision is >
6/36),balanced (+10.00D) or frosted glass is dispensed for
the phakic eye.
 The image magnification causes objects to appear closer
to the eye then they are really.
 Ii. Spherical aberration–Pincushion distortion

13.  Iii. Jack-in-the-box phenomenon–Due to prismatic
aberration a ring scotoma is produced all around the
edge of the lens. This causes an unseen object to
suddenly pop up in front of the eyes or disappear into
the ring scotoma, as the patient moves his eyes.
 Iv. Restricted visual field.
 V. Lack of physical coordination which results from
image magnification, restricted visual field, pincushion
distortion and Jack-in-the-box phenomenon.
 Vi. Thick, heavy lenses are cosmetically deficient

14. Contact Lens
 Advantages
 All the disadvantages of glasses are neutralised:
 i. Image magnification is 6–7%. Hence, binocular vision is possible in
uniocular aphakia.
 ii. Aberrations are lessened, i.e. Pincushion distortion, etc.
 iii. Increased visual field.
 Iv. Better physical coordination.
 V. Cosmetically attractive.
 Disadvantages
 i. Inability of elderly patients to insert and remove contact lens efficiently
 ii. Foreign body sensation.
 iii. Additional glasses required for reading correction. However, bifocal
contact lenses are available and becoming increasingly popular.

15. Secondary IOL Implantation
 Advantages
 i. Image minification is 0–2%. Hence, quick return to binocularity
is achieved due to minimum aniseikonia.
 Ii. Absence of aberrations.
 Iii. Restoration of normal peripheral field of vision.
 Iv. Excellent physical coordination

16.  Disadvantages
 It is significantly reduced to usual complications following primary IOL
implantation surgery, e.g. corneal decompensation, infection,
astigmatism, etc
 Secondary IOL implantation in aphakia may be;
 a. AC IOL implantation in aphakia following intracapsular cataract
extraction (ICCE )–If the aphakic eye was emmetropic earlier, AC IOL of
+18.00D strength is required to focus the image on the retina.
 b. PC IOL Implantation in aphakia following extracapsular cataract
extraction (ECCE) - +20.00D strength of PC IOL is required to focus the
image on the retina.
 c. Hyperopic LASIK.

17. Pseudophakia
 Pseudophakia means replacement of the natural crystalline lens by a
synthetic intraocular lens (IOL).
 MATERIALS OF IOL
 • Polymethyl Methacrylate (PMMA)
 • Silicon
 • Acrylic.
CALCULATION OF IOL POWER :- It is done by:
 • Axial length measurement by A-scan
 • Keratometry
 • Standard calculation formulas.

20. Residual Refractive Error
 Residual refractive error in pseudophakia consists of;
 • Spherical error–Accurate biometry overcomes this error.
 • Astigmatism–Phacoemulsification results in astigmatism against-the- rule,
whereas PC IOL implantation with sutures results in astigmatism with-the-
rule.
 • Loss of accommodation–However, nowadays multifocal IOL’s,
accommodative IOL’s are increasingly available to correct this error. After
phacoemulsification glasses may be advised after only one week and
after small incision cataract surgery (SICS) glasses may be advised after 3
weeks. However, after ECCE with PC IOL implantation glasses are advised
only after 6 weeks.

21. Thankyou