Correction of ametropia

PRESENTER :AMRIT JHA
SUBJECT CODE: MO101
Correction of Ametropia
©A Jha

What is ametropia ?
 Ametropia (a condition of ref. error) is defined as a state of refraction wherein the
parallel rays of light coming from infinity (with accommodation at rest) are focused
either in front or behind the retina, in one or both the meridian.
 Ametropia includes the following :
- Hypermetropia
- Myopia
- Astigmatism
©A Jha
Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

HYPERMETROPIA
 Light is focused behind retina, i.e. posterior focal point is behind the retina.
 Also known as long or far sightedness.
 AETIOLOGICAL TYPE :-
 Axial hypermetropia: 1mm axial length of eye shortening cause 3D hypermetropia.
 Curvatural hypermetropia: When the curvature of the cornea or lens is flatter than
normal. An increase of 1mm in its radius of curvature produces a hypermetropia of
6D.
 Index hypermetropia: It occurs due to change in refractive index of lens or cornea. It
may also occur in diabetic under treatment.
 Positional hypermetropia: Due to posteriorly placed lens. (Congenital or trauma)
 Absence of crystalline lens: Congenital or acquired. Leads to aphakia which is
condition of high hypermetropia.
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Continuation…
 CLINICAL TYPE :-
 Simple hypermetropia: It’s commonest form and is due to normal biological variation
in size and shape of eyeball. It could be axial or curvatural.
 Pathological hypermetropia:
(a) Congenital : Seen in conditions like; Microphthalmos, Microcornea, Congenital
aphakia etc.
(b) Acquired : It includes senile(curvatural or index), positional, aphakia,
consecutive, retrobulbar orbital tumer types of hypermetropia.
 Functional hypermetropia: It results from paralysis of accommodation as seen in
patients with 3rd nerve paralysis and internal ophthalmoplegia.
©A Jha

Components of Hypermetropia :
Total Hypermetropia: After complete cycloplegia with atropine.
Latent Hypermetropia: Amount of hypermetropia that is
corrected by tone of ciliary muscle.
Manifest Hypermetropia: Remaining amount of
Hypermetropia which is not corrected by tone of ciliary muscle.
Facultative Hypermetropia: Amount that can be corrected by
patient’s accommodative effort.
Absolute Hypermetropia: Residual amount of manifest hypermetropia.
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Continuation…
For example,
 If the patient having vision 6/9 improves with +0.50 DSph to 6/6, by fogging method,
patient reads 6/6 with +2.0 DSph and after a cycloplegic refraction patient reads 6/6
with +3.5DSph.
Find,
MH, AH, FH, LH, and TH ???
AH = +0.5 DS
MH = +2.0 DS (By fogging method) and TH = +3.5 DS (By cycloplegia)
Soln;
MH = AH+FH or, FH = MH – AH = +2.0 DS - +0.5 DS = + 1.50 DS
TH = MH +LH or, LH = TH-MH = 3.5 DS – 2.0DS = +1.50 DS
So, final correction by Donder’s formula
Rx = MH+1/3 LH = +2+1/3X1.5= +2+0.5 = +2.5DS
©A Jha

Clinical Pictures
SYMPTOMS SIGNS
1. Asymptomatic. If less than 1 D of
hyperopia.
1. Visual acuity varies with degree of
power and amount of accommodation.
2. Asthenopic symptoms like; tiredness
of eyes, frontal headache, watering etc.
2. Size of eyeball may appear small as a
whole or normal.
3.Defective vision with asthenopic
symptoms, if having 2-4 D of hyperopia.
3. Anterior chamber shallow and the angle
is narrow.
4. Defective vision only. When the
amount of hyperopia is more than 4 D.
4. Fundus examination may reveal
pseudopapillitis & foveal reflects at
greater distance from disc margin (+ve
angle kappa).
5. The effect of aging on Vision.
Occurrence of progressive loss of
accommodative power with ageing.
5. Shot silk appearance of retina and
abnormal branching of retinal vessels.
6. Intermittent sudden blurring of vision
and crossed-eye sensation.
6. A-scan biometry may reveal a short
anteroposterior length of the eyeball. ©A Jha

Treatment of hypermetropia
There are mainly 3 options and they are;
 Spectacle correction with convex lens.
 Contact lens.
 Surgical treatment.
1. Spectacle correction with convex lens:-
It is most common and easy method of correcting hypermetropia.
There are few fundamental rules for prescribing glasses and they are as follows:-
a. General rule: Total amount of hypermetropia should always be discovered by
performing cycloplegic refraction.
Correction is given only when patient is symptomatic in case of less than 1D.
b. For adults: Manifest correction must be given. Correction for infinity must be done
rather than for six meter examination room.
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b. For adults manifest hypermetropia correction this formula must be followed;
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c. For children:
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2. Correction with contact lenses:-
Advantage of CL over spectacles for Hypermetropia or, Aphakia;
a. Contact lenses (CL) are indicated in unilateral hypermetropia (anisometropia) mostly.
b. CL are cosmetically better.
c. CL provides increased, wider and field of view
d. Less magnification of image.
e. Elimination of aberration & prismatic effect of thick glass.
3. Surgical treatment:-
Surgical treatments for hypermetropia includes;
(a) Corneal refractive therapy. (b) Laser thermal keratoplasy. (c) Hyperopic LASIK or PRK
(d)Phakic IOLs.
©A Jha

APHAKIA
 Aphakia is one of causative factor for producing high degree of Hypermetropia.
 Aphakia literally means absence of crystalline lens from the pupillary area and do not
take part in refraction.
CAUSE :-
1. Congenital absence of lens.
2. Surgical aphakia
3. Traumatic extrusion
4. Posterior dislocation.
CLINICAL FEATURES:-
The only symptom in aphakia is marked defective vision for distance as well as for near.
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Continuation…
Signs of aphakia:-
1. Limbal scar in surgical aphakia.
2. Anterior chamber is deeper than normal.
3. Iridodonesis of iris can be seen
4. Pupil is jet black in colour.
5. Only two purkinje’s image is seen.
6. On slitlamp examination, absence of lens from pateller fosa is seen.
7. Fundus eamination shows hypermetropic small disc.
8. Retinoscopy reveals high hypermetropia.
©A Jha

Correction of aphakia.
Modalities for correcting aphakia includes;
 Spectacles
 Contact lens
 IOLs
 Refractive corneal surgery.
1. Spectacle Correction:- It is cheap, easy and safe method of correcting aphakia.
However, presently, it’s not common mode of correction due to it’s disadvantages.
Disadvantages of spectacle correction in aphakia:-
(a) Image magnification (b) Spherical aberrations. (c) Prismatic aberration
(d) Restricted field of vision. (e) Coloured vision. (f) Cosmetic blemish.
(g) Cumbersome to use. (h) Problem for near vision.
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2. Contact lenses :- Same as discussed in side 11(Hypermetropia).
3. IOLs Implantation:- IOL implantaion is the best available method of correction of
aphakia. Therefore, it is the commonest modality being employed nowadays.
4. Refractive Corneal Surgery:-
Refractive surgery is under trial for correction of
aphakia. It includes;
a. Keratophakia
b. Epikeratophakia
c. Hyperopic LASIK
©A Jha

MYOPIA
 Parallel rays of light coming from infinity are focused in front of the retina with acc. at rest
 Also known as short or near sightedness.
 AETIOLOGICAL TYPE :-
 Axial myopia: 1mm axial length of eye lengthening cause 3D myopia.
 Curvatural myopia: When the curvature of the cornea, lens or both are steeper than
normal radius of curvature produces a myopia of 6D.
 Index myopia: It occurs due to change increse in refractive index of lens due to nuclear
sclerosis.
 Positional myopia: Due to anteriorly placed lens. (Congenital or trauma)
 Myopia due to excessive accommodation: occurs in patient with spasm of
accommodation.
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Continuation…
 CLINICAL TYPE :-
 Congenital myopia:
1. It is usually associated with an increase in axial length and overall globe size.
2. Present since birth. It is usually diagnosed by age of 2-3 years of child.
3. High degree (8-10D) of error and mostly remains constant.
4. Most of time it’s unilateral as anisometropia.
5. Associations are like; Premature baby, Marfan syndrome, congenital convergent
squint , microphthalmos, aniridia, megalocornea, congenital separation of retina.
6. Treatment: Full cycloplegic refractive error including any astigmatic correction.
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Continuation…
 Simple or developmental myopia:
1. It is commonest variety of myopia and also known as physiological myopia.
2. Usually, the onset occurs at school going age 8-12 years of child. So, also called
school myopia.
3. Axial and curvatural type of simple myopia is considered with role of genitical,
physiological variation and under-development of the eyeball.
4. Symptoms include;
- Poor vision for distance,
- Half shutting of the eyes,
- Asthenopic symptoms like; development of convergence weakness, exophoria,
suppression in one eye, ciliary spasm, eye strain.
- Change in psychological outlook of myopic child. Becomes less active in outdoor
activity.
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5. Signs include;
- Predominant eyeball.
- Anterior chamber is slightly deeper than normal.
- Pupils are somewhat large and bit sluggishly reacting.
- Fundus is normal; rarely temporal myopic crescent may be seen.
- Magnitude of error. In simple myopia usually the error does not exceed 6-8 D.
 Acquired myopia: Some of the causes of acquired myopia are;
(1) Index myopia (2) Curvatural myopia (3) Positional myopia
(4) Consecutive Myopia (5) Pseudomyopia (6) Space Myopia
(7) Drug induced myopia
Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system. ©A Jha

Continuation…
 Pathological or degenerative myopia:
1. It is also known as progressive myopia. As, the name indicates, is a rapidly
progressive error which starts in childhood at 5-10 years of age and results in high
myopia (7-6 D).
2. Degenerative changes in eyes occurs at very early adulthood of child.
3. Results due to rapid Axial growth of eyeball which is not normal biological
developmental process.
4. It is linked with hereditary/ genetic factor and general growth process.
©A Jha

Clinical Pictures
SYMPTOMS SIGNS
1. Poor vision for distance.
Defective vision
1. Prominent eyeball and large cornea.
2. Change in psychological outlook . 2.Magnitude of refractive error increases
by about 4D yearly till age of 20 years.
3. Muscae volitantes and floating black
opacities in front of the eye.
3. Myopic crescent, optic disc appears
large & pale.
4. Progressive degenerative changes of
retina, choroid, sclera and vitreous.
4. Foster-Fuch’s spot are seen at the
macula & Cystoid degeneration at
periphery.
5.Night Blindness due to chorioretinal
degenerative changes.
5. Lattice degeneration and/or snail track
lesion may be associated.
6. Squeezing and half shutting of eyes to
create stenopic effect.
6. Posterior staphyloma due to ectasia of
sclera at posterior.
©A Jha

Treatment of Myopia
There are mainly 3 options and they are;
 Spectacle correction with concave lens.
 Contact lens.
 Surgical treatment.
1. Spectacle correction with concave lens:-
a. Basic rule of correcting myopia: Conversely to hypermetropia, the minimum
acceptance providing maximum vision should be prescribed in myopia.
b. Guidelines for correcting low degree of Myopia (upto -6.00 D) :
• In children up to 3 years of age, guideline shown in Table 3.2.
• In children above 3 years of age, myopia should be fully corrected and instructed to
use their glasses constantly. Never overcorrect myopia.
• In case of adult , younger than 30 years, if full correction over 3 D is not tolerated.
Then under correction must be done for present. Full correction may be given in future.
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Continuation…
2. Correction with Contact lens:
- It’s same as, advantage of contact lens over glasses discussed in hypermetropia.
- Contact lens helps to get rid off peripheral distortion and minification produced by high
myopic glass correction.
- Some authors report that wearing hard CL also slow down progression of myopia.
- Myope wearing a full contact lens correction needs more accommodation for near work
as compared with a spectacle wearer. So, they develop presbyopia comparatively
earlier.
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Continuation…
3. Correction by Surgical Treatment:
- It has become very popular nowadays.
- It should be performed after the error gets stabilized. Preferably after 18-20 years of
age.
- Few of the refractive surgeries for myopia correction are as follows;
(A) Keratorefractive procedure :
1. Incision procedure - Radial keratotomy.
2. Lamellar corneal refractive procedures – Epikeratoplasty, Smile technique etc.
3. Laser ablation corneal procedure – PRK, LASEK, LASIK etc.
4. Corneal implant.
5. Corneal tissue moulding – Orthokeratology.
(B) Lens based refractive procedure : PRLs and RLE.
(C) Combined refractive procedure : Bioptics and Trioptics.
©A Jha

Continuation…
4. Preventive measures :
a. Therapeutic interventions :
Atropine, even in low strength of 0.01% eye drops, instilled nightly are reported to
slow down the progression of myopia.
Pirenzepine 2% gel, applied twice a day, is also reported to slow down the myopia
progression.
b. Genetic counselling.
c. Visual hygine and balanced diet.
d. Low vision aids: These are indicated in patients of progressive myopia with advanced
degenerative changes, where useful vision is not obtained with glasses and CLs.
©A Jha

ASTIGMATISM
 Astigmatism is a refractive error in which the refraction varies in different meridian i.e.,
rays of light entering the eye cannot converge to a point focus but from focal lines.
 Aetiologically , astigmatism (Regular or Irregular ) can be defined as,
1. Corneal astigmatism: It is the result of abnormalities in curvature of cornea. It may be
congenital or acquired (occurrence is often irregular).
2. Lenticular astigmatism: It is comparatively rare.
a. Curvatural astigmatism: due to abnormal curvature of the lens. Eg: lenticonus.
b. Positional astigmatism: due to oblique placement or congenital tilting of the lens.
Eg: subluxation of the lens.
c. Index astigmatism: due to varriable refractive index of lens in different meridian.
Eg: diabetic patient developing nuclear sclerosis and/or cataract.
d. Retinal astigmatism: due to oblique placement of macula.
©A Jha

Regular Astigmatism.
 The astigmatism is regular when the refractive power changes uniformly from one
meridian to another (i.e. there are two principle meridian).
 Types of Regular astigmatism:-
1. With-the-rule astigmatism: Two principal meridian are placed at right angle to one
another, but the vertical meridian is more curved than horizontal.
2. Against-the-rule astigmatism: It refers to the astigmatic condition in which the horizontal
meridian is more curved than the vertical meridian.
3. Oblique astigmatism: It refers to the astigmatism where the two principal meridian are
not the horizontal and vertical, though these are at right angle to each other.
4. Bi-oblique astigmatism: In this type of regular astigmatism, the two principal meridia are
not at right angle to each other.
©A Jha

Refractive type of Regular astigmatism
1. Simple astigmatism :-
A. Simple myopic - Light ray focused on retina In one
meridian and in front of the retina in the another meridian.
B. Simple hyperopic - Light ray focused on retina In one
meridian and in behind of the retina in the another meridian.
2. Compound astigmatism :-
C. Compound myopic - Light rays in both the meridian are
focused in front of the retina.
D. Compound hyperopic - Light rays in both the meridian are
focused behind of the retina.
3. Mixed astigmatism :-
Light ray focused behind retina In one meridian and in
front of the retina in the another meridian.
©A Jha

Treatment of Astigmatism
Clinical Features : - Blurring of vision, Asthenopic symptoms, Tilting of head, Squinting
and half closure of the eye, Burning and itching of eye, Reading material may be held
close to eye etc.
Treatment:-
Optical correction :
1. The cylindrical lens may be prescribed in form of spectacles.
2. Hard CLs may correct up to 2-3 D of regular astigmatism.
3. Bi-oblique, mixed and Higher degree of astigmatism (regular or irregular) are better
treated by Contact lens/ toric CL than by spectacle.
Surgical treatment :
It is indicated in extensive very high astigmatism or corneal scarring(when vision does not
Improve with contact lens) and consists of penetrating keratoplasty, astigmatic LASIK etc.
©A Jha

©A Jha

Correction of ametropia

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