2. MYOPIA
• Short sightedness
• Myopia is a greek word meaning *close the
eye*
• Parallel rays of light coming from infinity are
focused in front of the retina.
• Accommodation is at rest
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3. Mechanism of production
Axial – increase anteroposterior length
Curvatural – increase corneal curvature
Positional – anterior placement of lens
Index – increase nuclear sclerosis
Myopia due to excessive accommodation
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4. Optics of myopia
Far point is finite (In front of the eye)
For emmetropic eye it is at infinity
Higher the myopia the shorter the distance
Far point is 1 mt. from the eye ,there is 1D of
myopia
Nodal point is further away from retina
Angle alpha- negative
resulting apparent
convergent squint
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6. CLINICAL CLASSIFICATION
Congenital Myopia
Simple Myopia
Degenerative Myopia
Nocturnal Myopia- insufficient contrast for an adequate
accommodative stimulus, the eye assumes the
intermediate dark focus accommodative position rather
than focusing for infinity.
Pseudo Myopia- overstimulation of the eye's
accommodative mechanism or ciliary spasm
Induced Myopia- exposure to various pharmaceutical
agents, variation in blood sugar levels, nuclear sclerosis
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7. DEGREE OF MYOPIA
Low Myopia(<3D)
Medium Myopia(3-6D)
High Myopia(>6D)
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8. AGE OF ONSET
Congenital Myopia (present at birth an
persisting through infancy)
Youth-Onset Myopia(<20 yrs of age)
Early Adult-Onset Myopia(20-40 yrs of age)
Late Adult-Onset Myopia(>40 yrs of age)
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9. Congenital myopia
Frequently seen in
-Premature babies
-Marfan’s syndrome
-Homocystinuria
Increase in axial length
Increase in Overall globe size
Since birth, diagnosed at age 2-3 years
If unilateral, as anisometropia, may develop
amblyopia, strabismus
Usually 8-10 D, remain constant
Bilateral- difficulty in distant vision, hold things very
close
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10. Associated conditions
Convergent squint
Cataract
Microphthalmos
Aniridia
Megalocornea
Management
Early Correction is desirable
Retinoscopy under full cycloplegia
Early full correction desirable
Poor prognosis
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11. Simple / developmental myopia
Physiological error not associated with any disease
of the eye
Etiology :
Normal biological variation in development of eye
Inherited –
Studies have shown a
33-60 percent prevalence of myopia both parent have
myopia.
the prevalence was 23-40 percent- one parent
neither parent has myopia, only 6-15 percent of the
children were myopic.
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12. Associated factors
Role of diet- (without any conclusive result)
excessive near work- Some studies have
found the prevalence of myopia increases
with income level and educational attainment,
and it is higher among persons who work in
occupations requiring a great deal of near
work.
A slightly higher prevalence of myopia in
females than in males.
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13. Clinical picture
Rarely present at birth
Rather born hypermetropic, become myopic
Begins at 7-10 years, stabilizing around mid
teens
Usually around 5D, never exceeds 8D
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14. Symptoms
Poor vision for distance, stenopaeic vision.
Asthenopic symptoms develop due to dissociation
between accommodation and convergence
Convergence weakness, exophoria, suppression
Excessive accommodation inducing ciliary spasm
and artificially increasing the amount of myopia
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15. Signs
Large and prominent globe
Deep AC
Large, sluggishly reacting pupils
Normal fundus, rarely crescent
Usually doesn't exceed 6-8D
Retinoscopy under full cycloplegia
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16. Pathological / degenerative / progressive
myopia
Rapidly progressive associated with
degenerative changes in the eye, starts at 5-10
yrs, result 6-7D myopia, prevelance – 2-3%
Etiology-
Rapid axial growth of the eyeball outside the
normal biological variations of development
Role of heredity linked retinal growth
Role of general growth process (nutritional,
hormonal, debilitating disease)
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17. Genetic factors General growth process
More growth of retina
Stretching of sclera
Increased axial length
Degeneration of choroid
Degeneration of retina features of
pathological
Degeneration of vitreous myopia
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19. Signs
Eye large, prominent eyes simulating
exophthalmos
Cornea large
AC deep
Lens show opacities at the posterior pole due to
aberration of lenticular metabolism and due to
overstretching.
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20. Vitreous degeneration,viterous
liquefication,vitreous detachment present as
Weiss reflux
Sclera thinning resulting in formation of post.
staphyloma
Visual field defects show Contraction and ring
scotomas are present
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21. DISC
Large in size
Myopic Crescent on the temporal side of the disc
Choroidal Crescent
Supertraction of the retina
Inverse myopia Myopic crescent situated nasally
and supertraction of the retina temporally called
as inverse crescent
Peripapillary atrophy
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25. GUIDELINES
LOW TO MODERATE DEGREES OF MYOPIA (UP TO -6D)
IN YOUNG SUBJECTS
Defect should never be overcorrected and advised for
constant use to avoid squinting and develop a normal
accommodation-convergence reflex
IN ADULTS
Receiving spectacle for the first time,have the ciliary
muscle that are unaccostomed to accommodate
efficiently so that lens of slightly lower power is
prescribed with which the patient has comfortable near
vision.
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26. FOR HIGH MYOPIA
DISPENSING SPECTACLES IN HIGH
MYOPIA
High index lens materials
Lighter lens materials
Reduced eyesize of selected frames
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• Full correction is given irrespective of age
along with duochrom balanced.
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Atropine— Recent well-designed studies using topical atropine
(myopin 0.01%), a non-selective muscarinic antagonist, have
demonstrated statistically and clinically significant reductions in the
progression of myopia. Although atropine is used in many countries in
Asia for slowing the progression of myopia, it is rarely used in the
United States for this purpose.
The side effects associated with atropine (e.g. photophobia,
cycloplegia) are considered by many clinicians to be unacceptable for
long-term therapy.
Pirenzepine— Pirenzepine, like atropine, is a
muscarinic antagonist but it is less likely to
produce mydriasis and cycloplegia,
Also show reduction in the progression of myopia
Pharmaceutical Agents
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Several large studies conducted in different parts of the
world have reported that the prevalence of myopia in
children with more outdoor activity hours is lower than in
children with fewer hours.
30. PHOTOREFRACTIVE KERATECTOMY (PRK)
Involves direct laser ablation of corneal stroma after
removal of corneal epithelium mechanically or
using a laser beam.
Done using Excimer laser
MUNNERLYN EQN: depth of ablation
(micrometer)=[diameter of optical zone(mm)]² ×
1/3power(Diopter)
For myopic a large amount of ablation is done in
central cornea than in the periphery.
Give good results for -2D to -6D of myopia
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31. LASIK (LASER ASSISTED IN SITU KERATOMILEUSIS)
Method:- Anterior flap of cornea is lifted with a keratome and
excimer laser is used to sculpt the stromal bed to change the
refractive error of eye
Corrects 0.5 to 12D of myopia and upto 8D of astigmatism
Guidelines:Age more than 18yrs
BCVA better than 6/12
Stable refraction for last 1yr
Absence of corneal disease & ectasia
Note:
In no case the residual bed thickness after the ablation should
measure 250microns so as to avoid central corneal ectasia
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33. Method:
Simple inexpensive procedure that
involves creation of epithelial flap after
exposure to 20% alcohol for 25sec &
subsequent replacement of flap after laser
ablation
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34. RK (RADIAL KERATOTOMY)
It refers to making deep corneal incisions(initially 16,now
down to 4) in the peripheral part of cornea leaving about
4mm central optical zone
The incisions are made almost down to the level of
Descemet’s Membrane
These incisions on healing flatten the central cornea thereby
reducing its refractive power
For low to moderate degree of myopia(-1.5 to -6D of
myopia)
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35. EPIKERATOPHAKIA
For high degree of myopia (upto 20D)
Method:
The epithelium is removed & then a pocket is fashioned
under the edge of the remaining epithelium & into this is
inserted the cryolathed donor homograft
Preserved material can also be used
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lens
36. NON CORNEAL INTERVENTIONS
(A) REMOVAL OF CLEAR LENS
We know that an aphakic eye is strongly hypermetropic
If an eye with an axial myopia of -24D is deprived of its lens
it will become emmetropic without any correcting lens.
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37. (b)Phakic intraocular lenses
An IOL of appropriate power is implanted inside
the eye without touching normal crystalline lens
thus without disturbing accomodation
Method can be used to correct both myopia &
hypermetropia
Phakic IOL types:
PC IOL
Angle supported IOL
Iris claw lens
ICL
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38. INTRA CORNEAL RING(ICR) IMPLANTATION
ICR implantation into the peripheral cornea approx.upto
2/3rd of stromal depth can also be considered for correction
of myopia
It results in a vaulting effect that flattens the central cornea
decreasing the myopia
The procedure has the advantage of being reversible
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