Myopia

• Myopia


  Short Sightedness
• Myopia


  A Greek word meaning "close the eye"
• Myopia


  • Parallel rays of light coming from infinity are focused in front of the retina
  • Accommodation is at rest
• Mechanism of Production


  1. Axial

  2. Curvature

  3. Index

  4. Myopia due to excessive accommodation
• Optics of Myopia


  • Far point is finite (in front of the eye)
  • Emmetropic eye is at infinity
  • Higher the myopia the shorter the distance
  • If far point is 1m from the eye, there is 1D of myopia
  • Accommodation need not develop normally resulting in Convergence Insufficiency and Exophoria
• Type of Classification


  • Clinical Classification
  • Degree of Myopia
  • Age of Onset
• Degree of Myopia


  • Low Myopia (less than 3D)
  • Medium Myopia (3-6D)
  • High Myopia (Greater than 6D)
• Age 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)
• Clinical Classification


  • Congenital Myopia
  • Simple Myopia
  • Degenerative Myopia
  • Nocturnal Myopia
  • Pseudo Myopia
  • Induced Myopia
• Congenital Myopia


  • Frequently seen in premature babies
  • Marfan's syndrome
  • Homocystinuria
  • Increase in axial length
  • Increase in overall 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
• Associated Conditions


  • Convergent squint
  • Cataract
  • Microphthalmos
  • Aniridia
  • Megalocornea
  • Congenital Separation of retina
• Management of Congenital Myopia

  • Early Correction is desirable
  • Retinoscopy under full cycloplegia
  • Early full correction desirable
  • Poor prognosis
• Simple/Developmental Myopia


  • Physiological error not associated with any disease of the eye
  • Etiology: Normal biological variation in development of eye
  • Inheritance
• Associated Factors


  • Role of diet
  • Theory of excessive near work
• Clinical Picture of Simple/Developmental Myopia

  • Rarely present at birth
  • Rather born hypermetropic, become myopic
  • Begins at 7-10 years, stabilizing around mid teens
  • Usually around 5D, never exceeds 8D
• Symptoms of Simple/Developmental Myopia

  • 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
• Signs of Simple/Developmental Myopia

  • Large and prominent
  • Deep Anterior Chamber
  • Large, sluggishly reacting pupils
  • Normal fundus, rarely crescent
  • Usually doesn't exceed 6-8D
  • Retinoscopy under full cycloplegia
• 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
• Genetic factors and General growth process

  • More growth of retina
  • Stretching of sclera
  • Increased axial length
  • Degeneration of choroid
  • Degeneration of retina
  • Degeneration of vitreous
• Symptoms of Pathological/Degenerative/Progressive Myopia

  • Defective vision
  • Muscae volitantes / floating black opacities
• Signs of Pathological/Degenerative/Progressive Myopia

  • 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
  • VITREOUS: degeneration, vitreous 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
• Posterior Staphyloma and Anterior Staphyloma

  • 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
• Pathological/Degenerative/Progressive Myopia Findings


  • MACULA: Foster-Fuchs fleck
  • RETINAL DETACHMENT
  • POSTERIOR STAPHYLOMA
  • RETINAL HOLES
  • TESSELATED FUNDUS
• Optical Treatment


  • Appropriate concave lenses
  • Minimum acceptance providing maximum vision
• 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
• Low Degrees of Myopia (Up to -6D) in Adults


  Receiving spectacle for the first time, have the ciliary muscle that are unaccustomed 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 near work is essential
• 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
• Dispensing Spectacles in High Myopia

  • High index lens materials
  • Lighter lens materials
  • Reduced eyesize of selected frames
  • Minus lenticular lens designs
• Advantages of Contact Lens

  • Contact lens provides cosmesis
  • Large retinal image size and slightly better visual acuity in severe myopia
• Surgical Treatment

  • Epikeratophakia
  • RK
  • PRK
  • ISCR
  • Phakic IOL's
  • LASIK
• 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
  • 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
• LASIK

  • Laser Assisted In situ Keratomileusis
  • 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
• LASEK


  • Laser subepithelial Keratomileusis
  • Indications: Low myopia, Irregular astigmatism, LASIK complications in contralateral eye, Thin corneal pachymetry, Predisposition to trauma, Glaucoma suspect
  • Method: Simple inexpensive procedure that involves creation of epithelial flap after exposure to 18% alcohol for 25sec & subsequent replacement of flap after laser ablation
• Radial Keratotomy (RK)


  • 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)
• 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
• Removal of Clear Lens


  • 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
  • Whenever surgery on clear lens is contemplated the eye is examined thoroughly for abnormalties like Raised IOP,Vitreous & retinal degeneration etc
• Phakic Intraocular Lenses

  • An IOL of appropriate power is implanted inside the eye without touching normal crystalline lens thus without disturbing accommodation
  • Method can be used to correct both myopia & hypermetropia
  • Phakic IOL types: PC IOL, Angle supported IOL, Iris claw lens
• Intrastromal Corneal Ring (ISCR) Implantation

  • ISCR 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