3. EMMETROPIA
• When parallel rays of light coming from infinity are focused in sensitive
layer of retina with accommodation being at rest.
• Components that maintain emmetropization are
axial length
AC depth
corneal curvature
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4. Myopia
ametropia
• Parallel rays of light coming from infinity (with accommodation at
rest) are focused either in front or behind retina.
Further classified into
Myopia :where the parallel rays of light coming from infinity are focused in
front of retina.
Hypermetropia: where the parallel rays of light are focused behind the sensitive
layer of retina.
Astigmatism :where the refraction varies in different meridia.
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6. Myopia
Derived from two Greek root words (Greek: μυωπία,
muōpia, from myein "to shut" – ops (gen. opos)
"eye“)
Myopia or shortsightedness is a type of refractive error in
which parallel rays of light coming from infinity are
focused in front of retina with the accommodation is at rest.
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7. Myopia
Optics of myopia
The optical system is too powerful for its axial length.
Image of distant object on retina is made up of circle of
diffusion formed by divergent beam since the parallel
rays of light coming from the infinity are focused in front
of the retina.
Far point is finite point in front of eye.
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8. Myopia
Optics of myopia
Nodal point is further away from retina.
Accommodation in uncorrected myopes is not developed
normally,they may suffer from convergence insufficiency,
exophoria,and early presbyopia as they grow.
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9. Myopia
Image formation
In myopia image formed in front of eye which is
corrected by placing the negative lenses.
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10. Myopia
TYPES OF MYOPIA
1. Etiologically
Axial myopia :result from increase in anterioposterior length
of eyeball.
Curvatural myopia :occurs due to increased curvature of
cornea or lens or both.
Index myopia :increase in refractive index of crystalline lens
assotiated with nuclear sclerosis.
myopia due to excessive accommodation :occurs in patients
with spasm of accommodation.
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11. Myopia
types of myopia contd…
2. Clinically,
3. congenital myopia.
4. simple or developmental myopia.
5. pathological or degenerative myopia.
6. acquired myopia.
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12. Myopia
Congenital myopia
Present since birth.
Seen more frequently in children who were born prematurely
or with various birth defects.
Usually error is about 8-10D, which mostly remains constant.
May sometimes be associated with other congenital anomalies
such as cataract, microphthalmos, aniridia, megalocornea.
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13. Myopia
Congenital myopia contd..
Early correction is desirable to help the children to
develop normal distance vision and perception of
world.
Full cycloplegic refractive error including any
astigmatic correction should be prescribed.
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14. Myopia
Simple myopia
Aka physiological or school myopia.
Physiological error not associated with any disease of eye.
Etiology:
result from normal biological variation in the development
of eye.
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15. Myopia
Simple myopia etiology
axial Physiological variation in
the length of the eyeball.
curvatural Underdevelopment of
eyeball.
----------------------------- Role of diet in early
childhood.
----------------------------- Theory of excessive near
work.
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16. Myopia
Simple myopia contd…
Clinical pictures:
Symptoms:
Poor vision for distance.
Asthenopic symptoms
eye strain due to dissociation between convergence and accommodation.
may develop convergence weakness and
exophoria and supression in one eye.
Change in psychological outlook.
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17. Myopia
Degree of myopia Visual acuity
-0.50 6/9-6/12
-1.00 6/18
-1.50 6/24
-2.00 6/36
-3.00 6/60
-4.00 4/60
-5.00 3/60
-6.00 2/60
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18. Myopia
Simple myopia: SIGNS
Eyes are large and prominent.
Slight deep anterior chamber.
Fundus is normal :rarely temporal myopic cresents
may be seen.
Usually error does not exceed 6-8D
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20. Myopia
Pathological myopia
Rapidly progressive error resulting in high myopia usually
apparent during 1st decade of life characterized by
increase in volume of posterior segment.
Etiology:
no satisfactory hypothesis has emerged to explain the
etiology of pathological myopia.
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21. Myopia
Pathological myopia contd
However it is confirmed that genetic factors play a major
role.
It is said that increased axial length, degenerative changes in
retina and vitreous, and pathological complications are
determined by different genes.
Inheritance can be AD, AR ,X-LINKED
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22. etiological hypothesis for pathological myopia
Genetic factors General growth
(play major role)
↓
More growth of retina
↓
Stretching of sclera
↓
Increased axial length
↓
Degeneration of choroid
↓
Degeneration of retina
↓
Degeneration of vitreous
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24. Myopia
Pathological myopia contd…
Signs:
Eyes are prominent, appearing elongated, and even stimulating an
exophthalmos.
Cornea is large and anterior chamber is deep.
Pupils are larger
Refractive error: increase by as much as 4.00D yearly stabilizes at
about the age of 20 but occasionally may progress until mid 30s``
frequently result in myopia of 10-20D
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25. Myopia
Retinal changes in pathological myopia
Optic disc:
appears large and pale
at temporal edge a characteristic myopic crescent present.
Degenerative changes:
in retina and choroid are common.
occurs tigroid appearance of fundus due to diffuse attenuation of the
RPE with visibility of large choroidal vessels.
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26. Myopia
Foster- Fuchs spot may be present at macula
It is a raised, circular, pigmented lesion developing after a subretinal
haemorrhage has been absorbed .
In advanced cases there occurs Focal chorio-retinal atrophy which
is characterized by visibility of the larger choroidal vessels and
eventually the sclera, total retinal atrophy, particularly at central
area.
There may be associated lattice degeneration and or snail track
lesions.
Retinal tears, haemorrhage , retinal detachment may be seen.
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27. Myopia
A posterior staphyloma is an ectasia or bulging of the posterior
sclera due to focal expansion and thinning .
It occurs in about a third of eyes with pathological myopia, and is
virtually always peripapillary or involves the macula.Staphyloma
development can be associated with macular hole formation.
Degenerative changes of vitreous include: liquefaction, vitreous
opacities, PVD appearing as weiss reflex.
Visual field shows contraction and sometimes ring scotoma may be
seen.
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28. Fundus changes in myopia
Peripheral retinal degernerations :
A:Lattice degeneration,
B:Snail track degeneration
C:Acquired retinoschisis
D:white-with-pressure
E:Focal pigment clumps
F:Diffuse chorioretinal degeneration
G:Peripheral cystoid degeneration
Choroidal neovascularization
associated with
a lacquer crack and high
myopia.
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29. Myopia
Pathological myopia :complications
Rhegmatogenous retinal detachment (RD) is much more common in high myopia, the
pathogenesis including increased frequency of posterior vitreous detachment, lattice
degeneration, asymptomatic atrophic holes, macular holes and occasionally giant retinal tears.
Foveal retinoschisis and macular retinal detachment without macular hole formation may
occur in highly myopic eyes with posterior staphyloma, probably as a result of vitreous
traction
Complicated cataract which may be either posterior subcapsular or early onset nuclear sclerotic.
Nuclear sclerosis.
Vitreous haemorrhages.
Choroidal haemorrhages and thrombosis.
Primary open angle glaucoma.
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30. Myopia
Systemic associations of high myopia
Down syndrome
Stickler syndrome
Marfan’s syndrome
Prematurity
Noonan syndrome
Ehlers–Danlos syndrome
Pierre–Robin syndrome
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31. Myopia
Acquired myopia
Causes:
index myopia : seen in nuclear sclerosis.
incipient cataract.
diabetic myopia occurs due to decrease in refractive index of cortex.
curvatural myopia -increase of corneal curvature in diseased conditions
like corneal ectasias, and conical cornea.
positional myopia: conditions producing anterior subluxation of lens.
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32. Myopia
Acquired myopia contd..
consecutive myopia -surgical overcorrection of
hypermetropia
pseudophakia with overcorrecting IOL.
Pseudomyopia -also called artificial myopia.
produced in a conditions such as excessive accommodation
and spasm of accommodation. may develop after too full
a hypermetropic correction in children.
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34. Myopia
Acquired myopia contd..
space myopia -experienced when the individual has no
stimulation for distance fixation.
never more than 0.75-1.50D
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35. Myopia
Acquired myopia contd…
Night myopia or twilight myopia
Shift from photopic to scotopic vision at twilight
Increased sensitivity to shorter wavelength of light
The emmetropic eye ,if accomodated for the middle range
of visusal spectrum,will be slightrly myopic for the
shorter wavelengths.
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36. Myopia
Acquired myopia contd…
drug induced myopia
cholinergic drugs such as pilocarpine, echothiopate,
di-isopropyl fluorophosphate.
sulphonamides.
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37. Myopia
types of myopia contd…
According to amount:
Classically:
Very low : upto – 1.00D
Low : –(1.00-3.00)D
Medium : –(3.00-6.00)D
High : –(6.00-10.00)D
Very high : above –10.00D
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38. Myopia
treatment of myopia
Optical treatment
Surgical treatment
General measures
Visual hygiene
Low-vision aids
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39. Myopia
Optical treatment
Include prescription of appropriate concave lens
minimum acceptance providing maximum vision
should be prescribed.
never overcorrect myopia
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40. Myopia
Optical treatment CONTD…
Guidelines for correcting low degree of myopia upto -6D
Children younger than 8yr should be fully corrected and
instructed to use their glasses constantly
Adult younger than 30 yrs: usually accept their ful
correction.
Older than 30 yrs: not able to tolerate a full correction over
3D if they have never worn glasses before. prescribe less
than full correction with which the patient has comfortable.
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41. Myopia
Optical treatment CONTD…
guidelines for correcting high myopia
full correction can rarely be tolerated.
undercorrect as little is compatible with comfort for binocular
near vision.
undercorrection to the tune of 1-3D or even more may be
required.
undercorrection is always better to avoid the problem of near
vision and minification of image.
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44. Myopia
Surgical treatment:
Radial keratotomy
Making deep (90 percent thickness radial incision in the
peripheral cornea leaving about 4mm central optical
zone.
On healing flattens central cornea there by reducing
refractive power|(refractive error between -1.5to -6D.
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45. Myopia
Photorefractive keratectomy
Photoablation of excimer LASER. Which can
accurately ablate corneal tissue to an exact depth with
minimal distortion of normal tissues.
Myopia is treated by ablating the central anterior
corneal surface so that it becomrs flatter.
Approximately 10 micron of ablation corrects 1D of
myopia.
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46. Myopia
LASIK
Laser in situ keratomileusis
Currently most frequent performed refractive procedure.
Can correct myopia upto -10D.
Automated microkeratone is used to raise corneal flap.
Excimer laser applied to stromal bed and flap again
repositioned.
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48. Myopia
Visual hygienes:
to avoid asthenopic symptoms
adequate illumination during close work
clarity of print should be good to avoid undue ocular
fatigue.
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49. Myopia
Low vision aids:
Indicated in patients of progressive myopia with
advanced degenerative changes where useful vision
cannot be obtained with spectacles and contact lenses.
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51. Myopia
prognosis
Simple myopia
o Prognosis is good.
o Error usually does not progress beyond 6-8D
o Stablizes by the age of 21
Pathological myopia:
o Visual prognosis is always guarded
o Possibility of progressiove visual loss due to degenerative
changes and danger of complications such as retinal detachment
should be borne in mind.
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