2. MYOPIA
Myopia results from an eye having excessive refractive power for its
axial length. This may be due either to the eye having a relatively long
axial length or to increased dioptric power of one or more of the
refractive elements.
the term myopia was derived by Galen (131-201 AD) from the words
myein ("to close")and ops ("eye"). Galen observed that nearsighted
people partially closed their eyes to see better
3. • Axial myopia
• if the total refractive power of an eye remains constant but the
axial length (i.e., the distance from the anterior corneal surface to
the retina measured along the visual axis) increases, a myopic
shift in refractive error will result
• Refractive myopia
•
if the axial length of an eye remains constant but the refractive
power of one or more of its optical elements increases, a myopic
shift in refractive status will occur.
4. • The proposed classifications may be grouped
under the following broad headings:
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1-Rate ofmyopic progression
2-Anatomical features of myopia
3-Degree of myopia
4-Physiological and pathological myopia
5-Hereditary and environmentally induced myopia
6-Theory of myopic development
7-Age of myopia onset
5. • Classification by Rate of Myopic Progression
• 1-Stationary myopia
• 2-temporarily progressive
• 3-permanently progressive.
6. • 1-Stationary myopiaStationary myopia
• is generally of low degree (-1.50 to -2.00 D) and arises "in the
years of development."
• The degree of myopia remains stationary during adulthood
and may occasionally diminish with the approach of old age.
7. • 2-temporarily progressive
• Temporarily progressive myopia generally arises in the early
teens and progresses until the late 20s.
• After this age, the rate of myopia progression approaches
zero. Interestingly, Donders reported that it was rare for
myopia to develop after 15 years of age in previously normal
eyes and, falsely, that it never developed after the 20th year
of life
8. • 3-permanently progressive
• Permanently progressive myopia ascends rapidly until
around 25 to 35 years of age, and there afteradvances
more slowly.
• Subsequent increases in myopia are said to occur in
jumps, rather than in a smooth progression.
• Donders observed that because of pathological conditions such as retinal detachment and macular degeneration, in these cases it was rare at 60 years of age "to
find a tolerably useful eye."
9. • Classification by the Anatomical Features of Myopia
• 1-Axial
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whereby the eye is too long for its refractive power
• 2-Refractive
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whereby the refractive system is too powerful for the axial length of the eye.An
increase in axial length may occur in the anterior or posterior portions of the
globe individually, or may occur throughout the eye.
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The site of elongation may have implications for determining the etiology. For
example, it has been suggested that expansion of the posterior portion of the
globe may be related to the actions of the superior and inferior oblique muscles
during vergence
10. • . Borish further divided refractive myopia into:1Index myopia, in which one or more of the
refractive indices of the media are anomalous.2Curvature myopia, in which the reduced radius
of curvature of one or more refractive surfaces
produces increased dioptric power.3-Anterior
chamber myopia, in which a decrease in anterior
chamber depth increases the refractive power of
the eye.
• Classification by the Anatomical Features of
Myopia
11. • Hirsch examined the refractive error of 562 eyes having at least -1.00 D of
• myopia in patients between 18 and 60 years of age. He divided the
population into three groups on the basis of the degree of myopia,
• 1-alpha
• Using inferential statistics, he determined that the alpha group followed a
normal distribution curve, with a theoretically assumed peak of -0.50 D.
12. • 2-beta groups
• The beta group was represented by a second
normal distribution curve, with its peak
around -4 D.
• Hirsch suggested that the myopia in this
group may be hereditary in origin
13. • 3-gamma groups
• The gamma group ranged from -9 to -15 D, and this degree
was described by Hirsch as malignant, pathological,
degenerative, or congenital.
• Sorsby et al in an investigation of 341 eyes between 20 and
60 years of age, concluded that 95% of refractive errors fell
within ±4 D. They also suggested that the etiology of myopia
of less than 4 D differed from that myopia exceeding 4 D,
15. • 1-Physiological myopia
• was denned by Curtin as myopia in which each component of refraction
lies within the normal distribution for that population. Thus, the myopia
arises from a failure of correlation between the refractive components.
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However, physiological myopia may be defined as normal as opposed to
pathologic myopia Therefore, physiological myopia might simply and more
accurately be defined as nonpathological myopia
16. • 2-Pathological Myopia(malignant or degenerative myopia)
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Duke-Elder and Abrams defined pathological refractive errors as "those refractive
anomalies determined by the presence in the optical system of the eye of an
element which lies outside the limits of the normal biological variations.
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These authors adopted the term degenerative myopia to describe myopia that is
accompanied by degenerative changes, particularly in the posterior segment of the
globe. This is most frequently found in high (>6 D) degrees of myopia
17. • Borish further divided refractive myopia into:
• 1-Index myopia
• in which one or more of the refractive indices of the media are
anomalous
• .2-Curvature myopia
• in which the reduced radius of curvature of one or more
refractive surfaces produces increased dioptric power
3-Anterior chamber myopia
• .
• in which a decrease in anterior chamber depth increases the
refractive power of the eye.
18. • Classification Based on Age of Onset
• 1-Congenital myopia:
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Myopia is present at birth and persists through infancy .although many children are
born with myopia (low birth weight) lose their myopia during first year of life this
classification includes only children whose myopia persist in infancy and present
when entering school. prevalence is about 2%.
• 2-Youth-onset myopia:
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The onset of myopia occurs between 6 years of age and the early teens .from 2% at
6 years to 20% at 20 years.
• 3-Early adult-onset myopia:
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The onset of myopia occurs between 20 and 40 years of age.
• 4-Late adult-onset myopia:
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Myopia onset occurs after 40 years of age.
19. • Other Myopias
• Night Myopia
• The phenomenon of increased myopia under low luminance
conditions was first reported in 1789 by the Revere and Nevil
Maskelyne More recent evidence has demonstrated that night
myopia is produced by an increased accommodative response
(typically on the order of 0.50 to 1.00 D) under degraded
stimulus conditions changes in chromatic aberration may also
be involved in this myopic shift.
20. • Pseudomyopia
• Pseudomyopia has been defined as a reversible form of myopia
that results from a spasm of the ciliary muscle.
• The excessive accommodative response produces an apparent
myopic shift that will disappear when a cycloplegic agent is
administered to produce relaxation of accommodation
22. • 1-Posterior staphyloma (ectasia)
• Axial enlargement ,mechanical stretching of posterior
choroids and sclera
• indication of a Posterior staphyloma:
• a-optic nerve crescents.
• b-myopic cupping of the optic nerve head
23. • Fundus manifestations in pathologic myopia
may include the following
• tilting of the optic disc
• peripapillary chorioretinal atrophy
• lacquer cracks
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spontaneous ruptures of the elastic lamina of Bruch’s membrane that appear yellowish white and are
usually located in the posterior pole with linear or stellate patterns FA may be useful in detecting subtle
lacquer cracks
• isolated, round, deep subretinal hemorrhages
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that clear spontaneously and are usually due to the occurrence or extension of a lacquer crack and not to
CNV
24. • Förster-Fuchs spotsdark spots due to subretinal or intraretinal RPE
hyperplasia, presumably developing in response to a small CNV that
does not progress
• posterior staphylomalocalized ectasia of the sclera, choroid, and RPE
• elongation and atrophy of the ciliary body
• gyrate areas of atrophy of the RPE and choroid
• cystoid, paving-stone, and lattice degeneration
• thinning or hole formation in the peripheral retina
• thinning and rearrangement of the collagen layers of the sclera
25.
26. • Some unfortunate consequences of myopia
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1-chorioretinal degeneration
2-retinal detachment
3-glaucoma
4-cataract
28. Pathologic Myopia
Eyes with pathologic myopia have progressive elongation of the
eye, thus creating a propensity for thinning of the RPE and choroid
The spherical equivalents of an eye with high myopia are more
than -6.00 D, or an axial length greater than 26.5 mm, whereas
patients with pathologic myopia are more than —8.00 D, or an
axial length greater than 32.5 mm.
33. Management
• Surgery
– Radial keratotomy (RK)
• Post-surgical complications
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Hyperopic shift
Diurnal fluctuations of refractive error and visual acuity
Glare
Corneal scarring
34. Management
• Refractive surgery
– Photorefractive keratectomy (PRK)
• Technique
– High energy photons from an excimer laser are used to
photoablate a small amount of tissue from the anterior
corneal surface and sculpt the cornea
35. Management
• Refractive surgery
– Photorefractive keratectomy (PRK)
• Post-surgical complications
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Eye pain
Corneal disruption
Blurry vision
Prolonged duration of drug use
Greater time needed for eyesight recovery
36. Management
• Refractive surgery
– Laser in-situ keratomileusis (LASIK)
• Technique
– A microkeratome is used to cut a flap of superficial corneal
tissue
– The flap is lifted back, exposing the underlying corneal stroma
– The excimer laser is used to perform tissue removal in the
corneal stroma
– The flap is repositioned in its original position and adheres to
the underlying corneal stroma without the need for sutures
37. Management
• Refractive surgery
– Laser in-situ keratomileusis (LASIK)
• Post-surgical complications
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Severe dry eye syndrome
Poor night vision
Reduced contrast sensitivity
Astigmatism
38. Management
• Refractive surgery
– Points to consider after the surgical procedure
• Use eyedrops, as prescribed by the ophthalmologist
• Be careful not to allow chlorinated water , shampoo, and sweat to
come into contact with the eyes
• Wear sunglasses when outside to protect the eyes from sunlight
• Remember to go back to the hospital for regular follow up visits
with the ophthalmologist and to get eyedrops
40. Pathological Conditions Associated with
Myopia
• Diabetes
– High blood glucose levels cause increased sorbital
levels in the lens
– Water rushes in and dilutes the sorbital in the lens
– Lens bulges and results in a myopic shift
41. Pathological Conditions Associated with
Myopia
• Marfan’s syndrome
– Suspensory ligaments break
– Subluxation of lens occurs superiorly and
temporally and results in a very high increase in
myopia
