Transcript MYOPIA ASTIGMATISM ANISOMETROPIA ANISEIKONIA

1
2
MYOPIA
• Short sightedness
• Myopia is a greek word meaning *close
the eye*
• Refractive error I
• Parallel rays of light coming from
infinity are focused in front of the
retina.
• Accommodation is at rest
3
 Mechanism of production
•
•
•
•
•
Axial
Curvatural
Positional
Index
Myopia due to excessive accommodation
4
 Optics of myopia
• Far point is finite (In front of the eye)
• Emmetropic eye it is at infinity
• Higher the myopia the shorter the distance
• Far point is 1mt from the eye ,there is 1D of
myopia
• Nodal point is further away from retina
Accommodation need not develop
normally resulting in
Convergence insufficiency
Exophoria
5
TYPES OF
CLASSIFICATION
• Clinical
Classification
• Degree of Myopia
• Age of Onset
6
Clinical Classification
•
•
•
•
•
•
Congenital Myopia
Simple Myopia
Degenerative Myopia
Nocturnal Myopia
Pseudo Myopia
Induced Myopia
7
Degree of Myopia
• Low Myopia(<3D)
• Medium Myopia(36D)
• High Myopia(>6D)
8
AGE OF ONSET
• Congenital Myopia
• Youth-Onset
Myopia(<20 yrs of age)
• Early Adult-Onset
Myopia(20-40 yrs of
age)
• Late Adult-Onset
Myopia(>40 yrs of age)
9
Congenital myopia
 Frequently seen in
 Premature babies
 Marfan’s syndrome
 Homocystinuria
 Increase in axial length
 Increase inOverall 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
10
 Associated conditions
 Convergent squint
 Cataract
 Microphthalmos
 Aniridia
 Megalocornea
 Congenital Separation of retina
Management
 Early Correction is desirable
 Retinoscopy under full cycloplegia
 Early full correction desirable
 Poor prognosis
11
• Simple / developmental myopia
 Physiological error not associated with any
disease of the eye
 Etiology :
 Normal biological variation in development of
eye
 Inheritence
12
Associated factors
Role of diet
Theory of excessive near work
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
14
Symptoms
Poor vision for distance
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
Psychological outlook
15
Signs
Large and prominent
Deep AC
Large, sluggishly reacting pupils
Normal fundus, rarely crescent
Usually doesn't exceed 6-8D
• Retinoscopy under full cycloplegia
16
• Pathological / degenerative /
progressive myopia
 Rapidly progressive associated with
degenerative changes in the eye
 Etiology
 Rapid axial growth of the eyeball outside the
normal biological variations of development
 Role of heredity
 Role of general growth process
17
Genetic factors
process
General growth
More growth of retina
Stretching of sclera
Increased axial length
Degeneration of choroid
Degeneration of retina
Degeneration of vitreous
18
Symptoms
Defective vision
Muscae volitantes / floating black
opacities
19
Signs
 EYE Large, prominent eyes simulating
exophthalmos
 CORNEA large
 ANTERIOR CHAMBER deep
 LENS show opacities at the posterior pole
due to aberration of lenticular metabolism
and due to overstretching anterior
dislocation may also occur
20
 VITEROUS degeneration,viterous
liquefication,vitreous detachment present
as WEISS REFLEX
 SCLERA thinning resulting in formation of
STAPHYLOMA
 VISUAL FIELD DEFECTS show Contraction
and in some ring scotomas present
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
22
 MACULA
Foster-Fuchs fleck
 RETINAL DETACHMENT
 POSTERIOR STAPHYLOMA
 RETINAL HOLES
 TESSELATED FUNDUS
23
24
25
26
Treatment
Optical treatment
Appropriate concave lenses
Minimum acceptance providing maximum
vision
27
Guidelines
LOW 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(1 or 2 D)
may be prescribed for reading,especially if engaged in to
any greater extent.Above the age of 40 years,when
accommodation fails physiologically, a weaker glass for
28
near work is essential
HIGH DEGREES OF MYOPIA
Full correction rarely be tolerated so we attempt to
reduce the correction as little as is compatible with
comfort for binocular vision. We prescribe the lens
with which the greatest visual acuity is obtained
without distress
29
30
ADVANTAGES OF SPECTACLES
Economical
Allow incorporation of prism,bifocals,pal
which can be used for the management
of esophoria or any accommodative
disorders accompanying myopia
Spectacles require less accommodation
than contact lens for myopia that
likelihood of accommodative asthenopia
or near point blur in patients
approaching presbyopia may be less
31
DISPENSING SPECTACLES IN HIGH
MYOPIA
•
•
•
•
High index lens materials
Lighter lens materials
Reduced eyesize of selected frames
Minus lenticular lens designs
32
ADVANTAGES OF CONTACT LENS
• Contact lens provides cosmosis
• Large retinal image size and slightly better visual
acuity in severe myopia
33
SURGICAL TREATMENT
 Epikeratophakia
 RK
 PRK
 ISCR
 Phakic IOL’S
 LASIK
RK
Phakic IOL’S
PRK
LASIK
ISCR
34
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 35
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:
• (1) In no case the residual bed thickness after the ablation
should measure 250microns so as to avoid central corneal
ectasia
• (2) Ideally the ablation should be done within 30sec of the
preparation of flap
36
LASEK
Laser subepithelial
Keratomileusis
•
•
•
•
Indications:
Low myopia
Irregular astigmatism
LASIK complications in contralateral
eye
• Thin corneal pachymetry
• Predisposition to trauma
• Glaucoma suspect
37
• Method:
• Simple inexpensive procedure that
involves creation of epithelial flap after
exposure to 18% alcohol for 25sec &
subsequent replacement of flap after
laser ablation
38
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)
39
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
40
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
• Note:
• Whenever surgery on clear lens is contemplated
the eye is examined thoroughly for abnormalties
like Raised IOP,Vitreous & retinal degeneration
etc
41
• (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
42
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
43
For Further Queries Contact :
Ms. Priyanka Singh
Head – Optometry Service
Email – [email protected]
44
Thank you
45