Download - Myopia refractive error
Myopia
DR. MEENANK
1. Definition
2. Etiology
3. Optics
4. Classification
5. Clinical varieties in detail
6. Treatment
Definetion
Myopia ( short sight ) condition where parallel rays come to focus in front of the sentient layer of retina when accommodation is at rest
Muopia (Greek) = To close the eye
History
Kepler (1611), Plempius (1632) - lengthening of posterior part.
Donders (1866) est.. Pathological basis, and detail clinical manifestation's
Etiology Axial : most commonest
1mm = 3D
Curvatural : cornea thickness causes astigmatism
1mm = 6D
eg : ectasies
conical cornea
lenticular curvature
eg : ant/post lenticonus – marked
Positional : dislocation of lens
Myopia due to excessive accommodation - spasm of accommodation,
suspensory lig. Rupture
Index myopia : change in the R.I of the crystalline lens
eg : Nuclear Sclerosis,
Incipient Cataract,
Diabetes.
Buphthalmos : cong/ infantile glaucoma.
Defective development – A.P diameter enlarged and
myopia not in ratio
Optics
Optical system – eye too powerful for axial length
Image of distant object on retina are circles of diffusion form by divergent beam
Far point is finite pt in front of eye – object at far pt focused without acc.
Angle of alpha –ve resulting in convergent squint
Accommodation- uncorrected- not developed , as not needed for Nv. Thus may develop exophoria, convergence insufficiency and presbyopia
Enlarged image is cause of nodal pt being far away from retina
Classification
myop
ia
Congenital myopia
Simple (or) Developmental
myopia
Pathological (or) Degenerative myopia
Acquired myopia
Congenital myopia
Since birth
Diagnosed – 2 -3 yrs.
Associated – prematurity, birth defects, congenital squint, and axial length
Unilateral or bilateral
Unilateral – manifest as anisometropia
diagnosed - after squint- amblyopia
Associated – cataract, microphthalmas, cong. Retinal separation, megalo-cornea
Prognosis – early detection
no 6/6 uni-ocular
Simple Myopia
Physiological / developmental / school
Biological variation in development
Limited progression no disease
Factors associated : Axial – A.P diameter (or) neurological
Curvatural – underdevelopment of eye ball
Diet – poor nutriention
Genetic influence – one (or) both parents
Simple Myopia
Physiological – A/S normal along with normal fundus
Intermittent – early signs of globe enlargement temporally
Sever category of intermittent – crescent with super-traction of disc
course
Born hyper metropic Emmetropic
• overshoot
Myopic
• 7-10 yrs
Stabilized at teens
• -5D to -8D
symptom's :
Poor distance vision – beyond far point impaired
Asthenopic sympt – eye strain due to difference b/w convergence and accommodation
Nv -No accommodation – convergence weakness – exophoria – suppression of one eye
Nv –convergence – excessive accommodation – ciliary spasm
Physiological out-look – myopic child behavior
Signs Eye – large and prominent
A.C. – deep
Pupil – large and sluggish
Fundus – normal
Error - -5.00 D to -8.00D
Diagnosis –visual acuity
subjective testing
retinoscopy
Pathological Myopia
Degenerative / progressive
2-3 %
More marked, high degree
Hereditary
Postnatal
Inc. progressive
Prevalence –
earlier and higher in females
higher – Asians, Arabs, Jews
lower – Africans, Caucasians
more in urban populations
Etiology
Results from rapid growth of eye out side its biological variation
2 theories
- Hereditary
- General growth Genetic factors
Retinal growth Scleral
stretchingIncrease in axial length
Pathological myopia• Degeneration – choroid, retinae,
vitreous
Symptoms Diminished Vn – progressive due to degeneration
Muscae volitantes – deg. lig. Vitreous
Night blindness – high myopes with choroidi-retinal changes
Signs Prominent, elongated(post), unilateral, stimulating
exophthalmos
Cornea – large; A.C – deep; pupil – large, sluggish
Refractive error – by -4D/yr up to 20-30yrs
Fundus – Generalized atrophy of choroid and retinae
Loss of RPE- fundus tugroid- prominent choroidal vessels
Choroid disappears – visible sclera – atrophic patch - post. Pole – macula (common)
Foster – Fuchs's spots – rare, sudden, dark pig.
sub-retinal neovascularization and choroidal hx.
Cystoid degeneration at periphery
Advance cases – total retinal atrophy, central
Lattice degeneration/ snail track lesion
Optic disc Myopic crescent – from elongation of disc
separation of retina and choroid from temp
may be annular
Super traction crescent – nasal retina extending over the disc – blur margin
Posterior staphyloma – higher degree,
herniation of post. Pole – sudden kinking of vessels at margin as in glaucoma
Vitreous – degeneration, PVD-Wiess reflex, liquefaction, opacities
Visual field – ring scotoma
Electo-retinograph – chorioretinol atrophy
Complications retinal tears, detachment, Hx (high myopia)
vitreous detachment, degeneration
complicated cataract –↓ lenticular metabolism
Nuclear sclerosis – common, effects refraction
Choroidal Hx – sever Vn loss if in fovea
POAG – not common but seen
acquired index – nuclear sclerosis, incipient cataract, diabetic myopia
Curvatural – true inc. in corneal curvature (or) lenticular
Positional – subluxation(ant) of lens
Consecutive – surgical overcorrection(cataract/ hypermetropia)
Pseudo-myopia – due to excessive accommodation and spasm of accommodation
Space myopia – no stimulus for Nv, its variable, trouble in flying and in fog
Night/twilight – shift from photic to scotopic vn is associated with inc. sensitivity to shorter wavelength viz myopic
Drug induced - Cholinergic – pilocarpine, echothiosulphate
Steroid – show changes in crystalline lens
Sulplanamides – changes the refractive indices in media
Diagnosis
presentation Simple – blurred Dv, constant/ transient, Nv may be normal, co-existing condt.
Nocturnal – blurred Dv in dim illumination, difficulty in driving
Pseudo myopia – transient Dv blur, inc after near work
Degenerative - considerable Dv blur, flashes/ floaters, Vn loss
Induced – transient Dv blur until drug effect, pupils constricted – cholinergic antagonist
Ocular examination
Visual acuity – both unaided Nv and Dv should be measured-mean gives reduced V.A
Refraction – retinoscopy or and A.R. , but A.R not qualitativeretinoscopy – diagnosis for nocturnal myopia with cyclopegics
Ocular motility, binocular Vn, accommodation – heterophoria, versions, accommodative facility test
systemic and ocular health – IOP, SLB, post-segment
Special test Fundus Photography
A and B scan
Visual field
Fasting blood sugars
Treatment
Optical Correction Proper correction with concave lens for image to fall on retina
Myopia up to -6.00D Children – full correction
Young adults – prevent over correction
Adults - ↓ 30 yrs. – full correction
↑ 30 yrs. – under corrected – ciliary muscles fail to accommodate
Spectacle's
Economical, safe
Allow incorporation
Better correction of astigmatism
Less acco- near pt. blur in presbyopia
Contact lens
Larger retinal image
Better Vn in Sr. myopia
Better visual field
Dec. prismatic effect
Rigid lens dec. progressive myopia
Surgical Treatment
Incisional – Radial Keratotomy
Lamellar corneal refractive Sx
Freeze keratomileusis of Barraque for myopia obsolete
Non-freeze keratomileusis
Keratomileusis insitu
Automated lamellar keratoplasty
Laser-based corneal refractive Sx
Photorefractive keratectomy (PRK)
Laser insitu keratomileusis (LASIK)
Custom Laser insitu keratomileusis (C-LASIK)
Epithelial Laser insitu keratomileusis (E-LASIK)
Miscellaneous corneal refractive Sx
Orthokeratology
Intracorneal contact lens
Intra stromal corneal ring segment
Intra ocular refractive procedure's
Phakic refractive lens
Refractive lens exchange
Radial keratotomyPhotorefractive keratectomy LASIK
Intraocular refractive procedure's
Radial keratotomy Deep radial incisions (90% thickness) sparing central 4mm –
cornea flatter's on healing
Disadvantages – globe rupture, irregular astigmatism, glare, bullous keratopathy
Photorefractive keratectomy (PRK)
De-epithelialzation – photo ablative0.5.1.0mm morePrevent extreme drying or wetting of cornea and residual islands
Ablation – 6mm for myopiaHand held ring for centration Laser should be coaxial with pupilToric photoabalation
corneal curvature shifts as ant stroma collapse and thins
Intrastromal PPk – double NdYAG Plasmamediated photodistribution shock wave
Complications – decentationCorneal haze, infiltrates, ulcersNight glare , halosDelayed epi healingIslands, Hx, IOP↑
First refractive procedure to use the excimer laser Max success in myopia Good for -2.00D to -6.00D Photoabalation of central optical zone of ant.
Corneal stroma
Combination – Incisional & Ablative Procedure
LASIK - Laser In Situ Keratomileusis
Microkeratome to make a corneal flap – excimer to ablate the refractive error
adv – bilateral, PRK healing risks avoided, stable results
Dis-adv – flap related, striae, diffuse lamellar keratitis, under (or) over correction
LASEK – LASER Epithelial Keratomileusis Similar to PRK – epithelium is removed and replace post Sx
Alcohol to store the epithelium
For large pupils and thin corneas
For > -8.00 D
Adv – no risk of flap dislocation (LASIK)
Thin flap
Less chance of ectasia
Dis- adv – visual recovery slower than LASIK
Epi LASIK Newer version of LASEK- advantage on LASIK
Cleaves epi from bowmen's – structural integrity maintained
More thin flap, less haze, faster recovery
Custom LASIK Customized for each eye
Less halos and glare, More chance of 6/6
Wave front aberrometer - corneal topography
Ablation – flexible laser system
Intra ocular refractive Sx
Refractive lens exchange Existing cataract and cornea unfit for refractive
Sx
For -16.00D to -30.00D
PCO reduced
Accommodation retained thrgh ‘hinges’
Phakic IOLs Patients not qualified for refractive Sx
Ant / Post chamber lens with out removing crystalline lens
Made of plastic (or) silicone
Management flow chart
Patient history and examination
Supplemental testing Assessment and diagnosis
Patient counseling and education
Treatment and management
Simple myopia
Correction
Infants and toddlers – no correction < 3DPre-school/early-school – correct if
>1-2DAdolescent's/
adults – correct significantly
Controlplus lens for NvRigid contact
lensVisual hygiene
ReductionCorneal
modification – refractive
Sx
Nocturnal myopia
Myopia correction for night
time seeing only
Pseudo-myopia
Reduction of accommodative
response – vision therapy,
plus lens for Nv, cycloplegic
agents, visual hygiene
Degenerative myopia
Correction and
management of retinal
changes
Induced myopia
Identification and
treatment of causative
agent
If a man is called to be a street sweeper,
he should sweep street so well that all the
host of heaven and earth will pause to
say, here lived a great street sweeper
who did his job well.
- Martin Luther King, Jr.