myopia
TRANSCRIPT
MYOPIA
PRESENTER – DR. OM PATEL
MODERATOR – DR. SURYAKANT JHA
SHORT SIGHTEDNESS
Condition in which incident parallel rays come to a focus anterior to the light sensitive layer of retina with accomodation at rest .
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
OPTICS OF MYOPIA
Accommodation in uncorrected myopes is not developed normally
May suffer from convergence insufficiency and exophoria
Early presbyopia
ETIOLOGICAL CLASSIFICATION
Axial : most commonest
1mm = 3D
Curvatural :
Increased corneal or lens curvature
1mm = 6D
Positional : Dislocation of lens
Myopia due to excessive accommodation : Spasm of accommodation,
Suspensory lig. Rupture
ETIOLOGICAL CLASSIFICATION
Index myopia :
Change in the R.I. of the crystalline lens
eg : Nuclear Sclerosis,
Incipient Cataract,
Diabetes.
ETIOLOGICAL CLASSIFICATION
DEGREE OF MYOPIA
Low Myopia(<3D)
Medium Myopia(3-6D)
High Myopia(>6D)
Congenital myopia
Simple or developmental myopia
Pathological or degenerative myopia
CLINICAL VARIETIES
Frequently associated with Premature babies Marfan’s syndrome Homocystinuria
Since birth,Diagnosed by 2-3 years
Increased axial length, overall globe size
If unilateral may produce amblyopia, strabismus
Bilateral – difficulty in distant vision, holds things closer
Usually error is 8-10 D, remains constant
CONGENITAL MYOPIA
Associated with
Cataract
Micropthalmos
Aniridia
Megalocornea
Congenital separation of retina
Management
Early full correction
Retinoscopy under full dilatation
CONGENITAL MYOPIA
Developmental myopia- commonest variety
School myopia (school going age 8-12 years)
Physiological, not associated with any eye disease
Normal biological variation in development
Rarely present from birth, rather hypermetropiafollowed by myopia
SIMPLE MYOPIA
Symptoms Poor vision for distance(short sightedness)
Asthenopic symptoms
Half shutting of eyes
CLINICAL PICTURE
Signs Prominent eyeballs
Anterior chamber - deeper than normal
Pupils- Large, sluggishly reacting
Fundus- normal; rarely temporal myopic crescent may be seen
Magnitude of refractive error Increasing at rate -0.5 +- 0.30/ year.
Does not exceed -6 to -8 D
DiagnosisConfirmed by performing retinoscopy
Degenerative/ progressive myopia
Rapidly progressive myopia associated with degenerative changes
Starts in childhood at 5-10 years of age
PATHOLOGICAL MYOPIA
ETIO-PATHOGENESIS
Genetic factors (play major role)
General growth process(minor)
More growth of retina
Stretching of sclera
Increase axial length
Degeneration of choroid
Degeneration of retina
Degeneration of vitreous
Defective vision
Muscae volitantes
Floating black opacities in front of eyes
Degenerated liquified vitreous
SYMPTOMS
Prominent eye balls
Elongation of eye ball mainly affects posterior pole and surrounding area
Cornea-large
Anterior chamber –deep
Pupils-slightly large,react sluggishly to light
Lens Opacities at the posterior pole due to aberration of lenticular metabolism
Anterior dislocation due to overstretching
SIGNS
Fundus examination:Optic disc
Large and pale
Temporal edge presents a characteristic MYOPIC CRESCENT
SUPER TRACTION CRESCENT may be present on nasal side (retina pulled over disc margin)
Peripapillary crescent encircling the disc may be present, where choroid and retina is distracted away from disc margin
Degenerative changes in retina and choroid
White atrophic patches at macula with a little heaping of pigment around them
• FOSTER-FUCH’S SPOT:• Dark red circular
patch due to sub-retinal neo vascularization and choroidalhaemorrhage
• Present at macula
• CYSTOID DEGENERATION – at periphery
Posterior staphyloma Due to ectasia of sclera at posterior pole
It may be apparent as an excavation with vessels bending backward over margins
Degenerative changes in vitreous Liquefaction
Vitreous opacities
Posterior vitreous detachment(PVD)- Weiss’ reflex
Visual fields Contraction
Ring scotoma may be seen
ERG reveals subnormal electroretinogram due to chorioretinal atrophy
Retinal detachment
Complicated cataract
Vitreous haemorrhage
Choroidal haemorrhage
Strabismus fixus convergence
COMPLICATIONS
Optical treatment of myopia Concave lenses
Basic rule – minimum acceptance providing maximum vision
Modes of prescribing concave lens-
1. Spectacles
2. Contact lens
TREATMENT OF MYOPIA
Contact lenses are used in case of high myopia as they avoid peripheral distortion and minification produced by strong concave spectacle lens
Radial keratotomy
Photo-Refractive keratectomy (PRK)
LASIK
Fucala’s lens extraction
ICL (Implantable Collamer Lens) or Phakic IOL
ICR ( Intra Corneal Ring implantation)
Orthokeratology
SURGICAL TREATMENT OF
MYOPIA
Radial keratotomy Obsolete now a days
Making deep radial incisions in peripheral part of cornea leaving the central a 4mm optical zone
These incisions on healing ; flatten the central cornea thereby reducing its refractive power
Correct low to moderate myopia(2-6D)
DISADVANTAGES:
Cornea is weakened – globe rupture in sports persons
Uneven healing – irregular astigmatism
Patient may feel glare at night
SURGICAL TREATMENT OF
MYOPIA
Photo refractive keratectomy (PRK)
A central optical zone of anterior corneal stroma is photoablatedusing excimer laser (193nm uv flash) to cause flattening of central cornea
Correction for -2 to -6D of myopia
Disadvantages:
• Post operative recovery is slow
• Pain and discomfort
• Residual corneal haze in centre affecting vision
• Expensive
Refractory surgery of choice for myopia of upto -12D
LASER ASSISTED IN-SITU KERATOMILEUSIS(LASIK)
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
1. Patients >20 years
2. Stable refraction for at least 12 months
3. Absence of corneal pathology
Absolute contraindication for LASIK Corneal thickness <450 micrometers
Presence of ectasia
PATIENT SELECTION CRITERIA
Customised(C)-LASIK:
Based on wave front technology
Corrects spherical, cylindrical and other aberations present in eye
Gives vision beyond 6/6 i.e.,6/5 or 6/4
ADVANCES IN LASIK
Epi-(E) LASIK:
Only epithelial sheet is separated with EpiedgeEpikeratome
Devoid of complications related to corneal stromal flap
Minimal or no postoperative pain
Recovery of vision is very early as compared to PRK
No risk of perforation during surgery and rupture of globe due to trauma like RK
No residual haze unlike PRK where subepithelialscarring may occur
LASIK is effective in correcting myopia of -12D
ADVANTAGES OF LASIK
Expensive
Requires greater surgical skill than RK and PRK
Flap related complications
Intraoperative flap amputation
Wrinkling of flap on repositioning
Postoperative flap dislocation/subluxation
Epithelization of flap – bed interface
Irregular astigmatism
DISADVANTAGES
Fucala’s operation
Myopia of -16D to -18D in unilateral cases
Clear lens extraction with intraocular lens implantation of appropriate power is the refractive surgery for myopia of >-12D
EXTRACTION OF CLEAR CRYSTALLINE LENS
Intraocular contact lens implantation for correction of myopia of >-12D
Special type of IOL is implanted in anterior chamber or posterior chamber anterior to natural crystalline lens
PHAKIC INTRAOCULAR LENS(ICL)
Into the peripheral cornea at approximately 2/3rd
stromal depth
Flattening of central cornea, decreasing myopia
Advantage: reversible procedure
INTRACORNEAL RING (ICR) IMPLANTATION
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
ORTHOKERATOLOGY