This document provides information about myopia (nearsightedness), including its optics, causes, types, signs and symptoms, examinations, complications, and treatments. It begins by explaining the optics of myopia where light rays focus in front of the retina. The causes of myopia are generally unknown but lengthy close work and genetics may be contributing factors. The document then discusses the different types of myopia in more detail and covers examinations like fundus exams to evaluate complications. It concludes by outlining both non-surgical and surgical treatment options for correcting myopic refractive errors.

2. What is Refraction
• When rays of light traveling through air enter a
denser transparent medium, the speed of light is
reduced and the light rays proceed at a different
angle, i.e., they are refracted.
• Except when the rays are normal
Refraction in Ophthalmology
• Methods for evaluating optical and refractive
state of the eye
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3. Emmetropia
• Parallel light rays coming from infinity are focused at the
plane of the retina when accomodation is at rest.
• Clear image of a distant object formed without any
internal adjustment of the optics of the eye.
• Absence of emmetropia = Ametropia
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4. Progress of refractive state of eye
• Birth : +2 to +3 D
• 90% of children at age 5 yrs are Hypermetropic
• 50% of children at age 16 yrs are Hypermetropic
• After the period of growth has passed , refractive state
tends to remain stationary, until in old age a further
tendency of hypermetropia is evident.
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5. Refractive data in adult
• Normal axial length ≈ 24 mm
• Change in axial length by 1mm = ±3D
• Refraction at corneal surface= +40 to 45(+43)D
• Change in Corneal Curvature by 1mm = ±6D
• Refraction by unaccomodated lens= +16 to
20(+17)D
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6. Angle kappa (κ)
κ (
F
M
B
N
D
Optic axis
• M = Macula
• D= Centre of pupil, on cornea
• N = Nodal point
κ = “Between the visual axis and pupillary line, hence roughly corresponds to
angle α”.
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7. Anomalies of the optical state of the eye
• Myopia
• Hypermetropia
• Astigmatism
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8. What is Myopia ?
• Diopteric condition of the eye
where parallel incident rays from
optical infinity
focus anterior to light sensitive layers
of retina
when accomodation is at rest.
• K/c/o shortsightedness
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9. Myopia – Optics
Diverging lens
Emmetropia
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10. Optics of Myopic eye
• Far point is at a finite distance inversely proportional to
the degree of myopia
• Weakest concave lens that diverges rays just sufficiently
to focus them at the retina is to be used
• Poor visual acuity is compensated to some extent by
enlarged image size due to the nodal point being further
from the retina
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11. Causes of Myopia
• The causes of myopia are not known.
• Epidemiological correlation suggest...
▫ Lengthy periods of close work are probably a
contributory factor
▫ There is some genetic predisposition to myopia and its
severity
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12. • Axial
• Curvature
• Index
• Positional
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13. Axial Myopia
• AP diameter increased to 25.5 to 32.5 mm
• 90-95% cases(commonest)
• 1mm=3D
• There may be…
▫ pseudoproptosis resulting from the abnormally large
anterior segment,
▫ a peripapillary myopic crescent from an exaggerated
scleral ring,
▫ posterior staphyloma
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14. Curvature Myopia
• Corneal curvature steeper than average, e.g.,
keratoconus,
• Radius <7-8.5 mm (normal)
• 1 mm=6 D
• Lens curvature is increased
• moderate to severe hyperglycemia (intumescence)
lenticonus (anterior/posterior)
spasm of accomodation
spherophakia
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15. Index Myopia
• Increased index of refraction in early to moderate
nuclear sclerotic cataracts in the elderly.
• Many people find themselves ultimately able to read
without glasses or having gained “second sight.”
• Decrease in refractive index of cortex – diabetic
myopia
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16. Positional Myopia
• Anterior movement of the lens is often seen after
glaucoma surgery and will increase the myopic error in
the eye.
• Axial myopia of buphthalmos is countered to a large
extent due to posterior displacement of lens-iris
diaphragm and flattening of the cornea
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17. GRADING OF MYOPIA
• Low myopia(<-3D)
• Moderate myopia(-3D to -6D)
• High myopia(>-6D)
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18. • Congenital
• Simple or developmental
• Pathological or degenerative
• Acquired(secondary myopia)
–post-traumatic
-post-keratitic
-drug-induced
-pseudomyopia
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19. Congenital myopia
• Since birth
• Diagnosed by 2-3 years
• Mostly unilateral
• Manifests as anisometropia
• Child may develop convergent squint in order
to preferentially see clear at its far point (10-12
cms)
• Associated with
cataract,microphthalmos,aniridia,megalocornea,
congenital separation of retina.
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20. Simple Myopia
• Rarely present at birth, but often begins to
develop as the child grows.
• Usually detected by age 8 or 12 years in school
vision tests (school myopia)
• May increase during years of growth, stabilizing
around the mid-teens, usually at about 5 D or
less.
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21. Pathological Myopia
• 2-3% population
• Increases by as much as 4 D/yr
• Usually stabilizes at about age 20 years and frequently
results in myopia – 10 to 20 D.
• If progress is rapid from age 15-20, likely to reach 20-30
dioptres
• Commoner in women, Jews and Japanese
• k/c/o degenerative/progressive myopia
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22. Pathological Myopia-Etiology
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23. 23

24. Symptoms
1.Defective vision
2.Muscae volitanes
• Floating black opacities in front of
eyes
• Degenerated liquified vitreous
3.Night blindness
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25. Signs
• Prominent eyeball-elongation of eyeball mainly affects
posterior pole and surrounding area
• Cornea –large
• Deep anterior chamber
• Large, sluggish pupil
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Elogation of eyeball posterior to equator

26. Fundus examination
• OPTIC DISC
-large and pale
-temporal edge presents as
a characteristic myopic
crescent
-peripapillary crescent
encircling the disc may be
present
-super traction crescent
may be present on nasal
side(retina pulled over disc
margin)
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27. 27

28. Fundus examination
• DEGENERATIVE CHANGES
IN RETINA AND CHOROID
-common in progressive myopia
-chorioretinal atrophic patches at the
macula
-Foster-fuch’s spot
-Cystoid degeneration-periphery
-Lattice degeneration
-Total retinal atrophy
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29. 29

30. Lattice degeneration
Figure:
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31. Lattice, snailtrack, retinoschisis, white without
pressure
Snailtrack Retinoschisis
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32. Posterior staphyloma
• Ectasia of sclera at posterior pole
• Crescentric shadow 2-3 DD temporal to disc,
• Sudden kinking of retinal vessels as they dip over the edges,
• Gross atrophy
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33. Peripheral
Degenerations
Paving stone
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34. • DEGENERATIVE
CHANGES IN
VITREOUS
-Liquefaction
-Vitreous opacities
-Posterior vitreous
detachment(PVD)-Weiss
reflex
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35. • VISUAL FIELDS
-contraction
-ring scotoma
• ERG –subnormal electroretinogram due to
chorioretinal atrophy
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36. Complications
• Retinal detachment
• Complicated cataract
• Vitreous haemorrhage
• Choroidal haemorrhage
• Strabismus fixus convergence
Horseshoe Tear
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37. 1.)Optical treatment of myopia
Concave lens
-Basic rule-minimum acceptance providing
maximum vision
-Modes of prescribing concave lens
▫ Spectacles
▫ Contact lens
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38. 38

39. 2.)Refractive surgery
A.Cornea based procedure B.Lens based procedure
1.Radial keratotomy(RK)
2.Laser ablation corneal
procedures
a.Photorefractive keratectomy
b.LASIK
c.ReLEx
d.ICR implantation
e.Orthokeratology
1.Refractive lens exchange
2.Phakic refractive lens(PRL)
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40. Radial keratotomy
• Deep radial incisions in peripheral part of
cornea leaving the central 4mm optical zone
• Incisions on healing-flatten the central cornea
,thus reduces refractive power
• Correct low to moderate myopia(-2 to -6 D )
• Disadv-cornea is weakened
-uneven healing-irregular astigmatism
-glare at night
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41. Photorefractive
keratectomy(PRK)
• Central optical zone of anterior
corneal stroma is photoablated
using EXCIMER laser(193 nm UV
flash) to cause flattening of central
cornea
• Correction for -2 to -6 D of myopia
• Disadv-pain and discomfort
-post-op recovery is slow
-residual corneal haze in
centre affects vision
-expensive
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42. LASIK(Laser assisted in-situ
keartomileusis)
• Flap of 130-160 micron thickness of anterior
corneal tissue is raised
• Midstromal tissue is ablated directly with an
excimer laser beam
• Ultimately flattening the cornea
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43. • Advan-
-no post-op pain
-early post-op recovery
-no risk of perforation during surgery
-no residual haze like PRK
-effective for correcting myopia of -12D
• Disadv-
-expensive
-requires surgical skills
-flap related complications
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44. • PATIENT SELECTION CRITERIA
1.Patient >20yrs
2.Stable refraction for atleast 12 months
3.Absence of corneal pathology
• ABSOLUTE CONTRAINDICATION FOR LASIK
1.Corneal thickness <450 micrometers
2.Presence of ectasia
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45. Refractive lenticule
extraction(ReLEx)
• All-femtolaser-vision-correction
• Lenticule of corneal stroma is extracted with
femtosecond laser
• Correct myopia upto -10D
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46. Intracorneal ring (ICR)
implantation
• Into the peripheral cornea at approximately
2/3rd stromal depth.
• Flattening of central cornea,decreasing myopia.
• Advantage-reversible procedure
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47. Orthokeratology
• A non-surgical reversible method of moulding
the cornea with overnight wear unique rigid gas
permeable contact lenses.
• Myopia correction upto -5D
• Used in patients below 18 years of age
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48. Extraction of clear crystalline
lens
• Fucala’s operation
• Myopia of -16 to -18 D in unilateral cases
• Clear lens extraction with IOL implantztion of
appropriate power is the refractive surgery for
myopia of >-12D
• Complications-endophthalmitis,after
cataract,retinal detachment
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49. Phakic refractive lens (PRL)
• Intraocular contact lens implantation for
correction of myopia >-8D
• Special type of IOL is implanted in anterior
chamber or posterior chamber to natural
crystalline lens.
• Complications-
endophthalimitis,iridocyclitis,cataract,secondary
glaucoma
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50. 3.)GENERAL MEASURES-
-Balanced diet rich in vitamins and proteins
-Early management of associated debilitating
disease
-Visual hygiene
4.)LOW VISION AIDS
-In patients with progressive myopia with
advanced degenerative changes
5.)PROPHYLAXIS
-Genetic counselling
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51. Thank you
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