Transcript Axial Myopia

In the name of ALLAH, most gracious, most merciful
MYOPIA
BY: SUMAYYA NASEEM
Internee Optometrist
AIMS & OBJECTIVES OF TODAY’S LECTURE
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Myopia and its etiology
Mechanisms of production
Clinical types
Signs & symptoms
Complications
Diagnosis
Correction
Prevention
HUMAN EYE:OPTICAL CONDITIONS
Emmetropia
Ametropia
Index
Presbyopia
Axial
Curvature
Myopia
Hyperopia
Parallel incident light is
Parallel incident light is
focused
behind the retina
focused in front of the retina
Astigmatism
We get 2 focal points
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EMMETROPIA
Parallel incident rays come to a focus on
the retina when the accomodation is fully
relaxed so far point is at infinity.
OPTICS OF EMMETROPIA
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AMMETROPIA
Parallel incident rays do not come to a focus
on the retina when the accomodation is fully
relaxed so far point is not at infinity.
MYOPIA
(short sightedness, hypometropia)
A type of refractive error in which Parallel
incident light is brought to a focus in
front of the retina when eye is at rest. So
far point is at finite distance.
AETIOLOGY
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Hereditary (Genetic Factor)
Role of diet
Theory of excessive near work
Reading posture
Racial (Chinese and Japanese highest)
• Environmental Factors
MECHANISMS OF PRODUCTION
1. Axial myopia
• Increased length of eyeball
• 1mm=3D
2. Curvature myopia
• Increased curve of cornea e.g. conical cornea
• Increased curve of lens e.g. lenticonus
• 1mm=6D
3. Positional myopia
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Anterior displacement of lens e.g. trauma
4. Index myopia
• Increase in ref index of lens e.g. nuclear sclerosis in
diabetes
• Increase in ref index of aqueous humor
• Decrease in ref index of vitreous humor e.g. vitreous
liquefication
5. Myopia due to excessive accomodation
• Patients with excessive accomodation
MYOPIA: REFRACTIVE vs AXIAL
Refractive Myopia
(Optics of the eye too strong)
Axial Myopia
(Eye too long)
Image of distant object & near object
CLINICAL VARIETIES OF MYOPIA
1. Congenital myopia
2. Simple or developmental myopia
3. Pathological or degenerative myopia
4. Acquired myopia
CLINICAL VARIETIES OF MYOPIA
1. Congenital myopia
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Present since birth
Diagnosed at 2-3 years
Common in children born with Marfan’s syndrome
Mostly unilateral and anisometropic
Rarely bilateral
Usually 8-10 D and constant
May be associated with aniridia, megalocornea and
congenital separation of retina
2. Simple myopia
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Commonest
Not associated with any eye disease
Error usually does not exceed 6D
Usually begins at age of 7 to 10 years
Stabilizes around midteens
CLINICAL PICTURE
Symptoms
• Poor vision for distance
• Asthenopic symptoms
(due to dissociation b/w accomodation and
convergence)
• Change in physiological outlook of
children
SIGNS
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Myopic eyes are large
Anterior chamber is deeper than normal
Pupil is dilated and sluggish
Fundus is normal
Does not exceed 6D
Normal near vision
Defective distant vision
3. PATHOLOGICAL MYOPIA
• Rapidly progressing error
• Associated with degenerative changes in posterior
segment
• Rapid axial growth of eyeball
• Usually Hereditary in nature
• Can exceed till 30 D
• Ref error increases 4D yearly
• Also known as degenerative myopia.
CLINICAL PICTURE
Symptoms
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Defective distant vision
Defective near vision if degeneration starts
Muscae volitantes (Flying Flies)
Night blindness
MUSCAE VOLITANTES
SIGNS
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Prominent eyes
Proptosis if error exceeds 20D
Cornea large
a/c deep
Pupil large and sluggish
Sclera is thin
Posterior
Subcapsular Cataract
Open-Angle Glaucoma
Idiopathic Retinal
Detachment
Chorioretinal
Degeneration
OPHTHALMOSCOPICALLY
Changes in vitreous
• Liquefication
• Floaters
• Vitreous detachment
POSTERIOR VITREOUS DETACHMENT
VITREOUS DETACHMENT
CHOROIDAL AND RETINAL CHANGES
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Degeneration of choroid
Choroidal hemorrhage
White atrophic patches
Tilted disc
Posterior staphyloma
Myopic crescent (temporally)
Forster-Fuchs flecks (subretinal neovascularisation &
pigmented lesion at or near the fovea)
POSTERIOR STAPHYLOMA
TILTED DISC
CHOROIDAL AND RETINAL DEGENERATIONS
MYOPIC CRESCENT
HIGHLY MYOPIC FUNDUS
COMPLICATIONS
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Retinal tears
Retinal detachment
Hemorrhages
Complicated cataract
Vitreous hemorrhage
Primary open angle glaucoma
Visual field shows contraction
Scotoma can be seen
RETINAL DETACHMENT
RETINAL DETACHMENT
VISUAL FIELD LOSS
4. ACQUIRED MYOPIA
Some causes are as follows:
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Index myopia (diabetic, nuclear sclerosis)
2. Curvature myopia (conical cornea & corneal ectasias)
3. Positional myopia (ant. Subluxation of lens)
4. Consecutive myopia (surgical overcorrection)
5. Night myopia (as pupil dilates)
6. Drug induced myopia (pilocarpine, steroids)
7. Pseudo myopia (excessive & spasm of accomodation)
REFRACTION PROCEDURE
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VA with and without correction monocularly
Pinhole VA
Cover test with and without correction
Quick ophthalmoscopy
Retinoscopy
Subjective verification:
• Duochrome test
• Muscle balance- Maddox rod for distance
DISTANCE VA CHART
Bailey-Lovie Chart
University of Waterloo
distance VA chart
RETINOSCOPIC FINDINGS
During retinoscopy of a
myopic patient, ‘against’
movement of reflex is seen as
compared to retinoscopic
light or streak.
Against movement is
neutralized by negative or
concave lenses.
Reflex motion seen during retinoscopy
“with”
“neutrality”
“against”
Retinoscopy Reflex
RETINOSCOPY: SET-UP
DUOCHROME TEST
Letters
Circles
COVER/UNCOVER TEST
MADDOX ROD
PHOROPTER (MANUAL REFRACTOR)
VISUAL FUNCTIONS ASSESSMENT
OPTICAL CORRECTION OF MYOPIA
Options are as follows:
• Spectacles and LVD’s
• Contact lenses
• Refractive surgeries
• Laser
Others:
• Visual hygiene
• Prophylaxis
• General measures
SPECTACLES
• Minus lenses (CONCAVE) are used to correct myopia
• In high numbers glasses are not cosmetically attractive
and minify actual pt eye size for others
• Myopes are usually kept under corrected so that there
accomodation is not stimulated. Otherwise, they will
complain of Asthenopic symptoms
EXTREME MYOPIA
CONTACT LENS
Contact lens is a better option for correction of high
myopia both optically and cosmetically..
C/L INSERTION & REMOVAL
A SOFT C/L
LOW VISION DEVICES (LVD’s)
READING GLASSES
HAND MAGNIFIERS & STAND MAGNIFIERS
DOME/PAPERWEIGHT MAGNIFIER
FILTERS
TELESCOPES
ORTHOKERATOLOGY
• Orthokeratology is defined as, the reduction,
modification, or elimination of visual defect by
the programmed application of contact lenses
• Orthokeratology uses hard Contact Lenses to
remould the Cornea, to reduce or correct Myopic
(short-sighted) and Astigmatic (irregular surface)
errors of the eye.
• In some ways this is similar to the use of dental
braces by an Orthodontist to straighten crooked
teeth.
• The main difference is that if a tooth position is
corrected for some months it will stay in the new
position. However the Cornea is highly elastic, and
always returns to its original shape.
• For this reason the lenses are worn nightly or on
alternate nights after the ideal Corneal shape has
been achieved and removed in the morning giving
perfect vision without the need for spectacles or
contact lenses.
• Once the desired level of V.A has been
achieved a of retainer lens wear is initiated
until cornea reaches the level of stability new
shape cornea. Lens wear is then gradually
reduced to the minimum, required to attain
good functional vision through out the day.
• The amount of ametropia that can be
corrected using orthokeratology is: –1 to –6 D
myopia with 1.5 D of WTR astigmatism and
0.75 D of ATR astigmatism.
ORTHOKERATOLOGY CONTACT LENS
SURGERY
Clear lens extraction:
• For myopia of greater than 15-20 D, cataract
surgical procedure is applied and noncataractous lens is removed and intra ocular
lens of calculated power is inserted.
Phakic IOL:
• IOL is also placed in A/C or P/C of phakic
eyes to correct the refractive error.
CATARACT SURGICAL PROCEDURE
LASER AND SURGERIES
Photorefractive keratectomy PRK:
• Uses Excimer laser to change ant. curvature of
cornea.
• Tissue is ablated centrally 3.5-4mm and surface
curvature is reduced.
• After scarring, haloes, glare and reduction of best VA
are the complaints of patient.
PHOTOREFRACTIVE KERATECTOMY PRK
LASER ASSISTED IN SITU KERATOMILEUSIS
LASIK
• A mechanical keratotome is used to dissect through
the superficial corneal stroma and fashion a lamellar
circular flap of uniform thickness.
• The bared corneal stroma is reshaped using Excimer
laser and hinged flap is replaced.
• Better than PRK because of little scarring and better
correction predictability.
LASER ASSISTED IN SITU KERATOMILEUSIS
LASIK
Flap creation
Laser intervention
Flap repositioning
CORRECTION WITH LASIK & PRK
Myopia
• -1D to -6D --------- PRK
• -6D to -12D -------- LASIK
(better to wait till the patient reaches the age of 21 years)
EXCIMER SYSTEM
LASIK
EPIKERATOPHAKIA
• This uncommon surgical technique creates a
new corneal surface with a different surface
curvature by attaching a lenticule of preshaped donor corneal stroma to the surface of
host cornea.
• The eye is not entered and procedure is easily
reversed by removal of lenticule.
EPIKERATOPHAKIA
KERATOMILEUSIS
• It is the use of microkeratotome to remove
lamella of ant. corneal stroma which is then
reshaped on a cryolathe before being
replaced.
• High degrees of myopia till 15D can be
corrected in this way.
• Keratophakia is developed as a modification
of keratomileusis and is used for aphakia.
KERATOMILEUSIS
PREVENTION & CONTROL OF MYOPIA
• Many people believe that too much close work, such
as reading or sitting too close to the television, causes
nearsightedness. But there was little evidence to
support this belief. However, one study suggested
that people in professions that involve extensive
reading have higher degrees of nearsightedness.
• With regular instillation, topical 0.05% atropine is an
effective agent for controlling myopia progression in
a majority of school aged children.
• Nutritional Factors
• Since the eye has a collagenous structure, it seems
likely that the same nutrients which strengthen
collagen might also be helpful in keeping the eye from
becoming elongated. Calcium, magnesium, boron,
silica, selenium, manganese and vitamin D all come
to mind, as well as vitamin C. A strong ocular
structure would likely be less prone to becoming
elongated, as occurs in myopia. Low levels of calcium,
fluoride and selenium were found to be related to
increased risk of progressive myopia in an
exploratory study.
• Vitamin E, can slow the progression of myopia in
children. Myopia in children was also significantly
related to lower consumption of protein, fat,
vitamins B1, B2 and C, phosphorus, iron, and
cholesterol.
VISUAL HYGEINE
• We should insist that our children use good lighting
and good posture when reading, take frequent eye
rest breaks during long study periods, and encourage
them to be physically active.
• Environmental visual stress may be lessened by
taking these precautions while reading: frequently
stretching and moving the eyes and looking away
from the reading material at distant objects,
removing distance eyewear(-) or using reading
glasses for near tasks.
• As it is usually hereditary in nature, so family
marriages should be avoided.
REFERENCES
• Theory and practice of optics and refraction
by A K Khurana
• Duke Elder's Practice of refraction (Tenth
edition)
• Clinical Optics by Elkington, Frank and
Greaney (Third edition)
• www.visionlaser.com
• www.orthokeratology.com
and many other websites.