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Near Sightedness
 
MYOPIA OR NEARSIGHTEDNESS OR SHORTSIGHTEDNESS
 
 
What is Myopia or nearsightedness/shortsightedness?
Myopia is a refractive error wherein the parallel rays of light, coming from infinity, after refraction through the eye, come to a point focus in front of the retina, when the accommodation is at rest.
 
 
What causes myopia?
Different types of causes:-
  • Axial myopia: - Normal axial length (adult) is 24mm. If the eyeball grows larger it causes axial myopia (1mm=6D).
  • Curvature myopia: - Increased curvature of cornea or less frequently the lens causes myopia. (0.1=3D) Ex: Keratinous. Anterior and posterior lenticonus.
  • Index myopia: - Ex.: Nuclear cataract: When the eye is otherwise normal increased refractive index of the nucleus of the lens causes myopia.
  • Anterior dislocation of the lens
 
What is simple myopia?
 

 
 

Axial and curvature myopia are seen in young subjects but index myopia in the elderly. Myopia of less than -6D is called simple myopia and it is just an error of refraction

 
What is pathological myopia?
Myopia of more than -6D is a degenerative disease and is called pathological myopia or high myopia.
 
  •   This is a degenerative disease. Why premature degeneration in such young subjects? unknown but with a definite hereditary pattern.
  •   Posterior half of the eyeball including the vitreous shows degenerative changes.
  •   Usually starts in early childhood.
  •   Myopia usually exceeds -6D. But in few patients this may simple myopia <-6D be as high as -25D to -30
 
What are the symptoms?
 
  • Defective distant vision near vision being normal.
  •   Seeing black floaters in front of the eye (due to vitreous degeneration and opacities).
  •   Defective central field or sometimes peripheral visual field.
 
What are the FINDINGS IN CLINICAL PATHOLOGY?
 

(I) Anterior segment shows

(1)   Large prominent eyeball.

(2)   Cornea flatter

(3)   Anterior chamber deep.

(4)   Pupil larger.
 

(II) Fundus findings in pathological myopia

=     Large optic disc

(1)   Temporal myopia erescent.

(2)   Nasal supertraction erescent

(3)   Foster fuch’s flacks (FFF).

(4)   White patches of choroidal atrophy

(5)   Lattice Degeneration

(6)   cyestoid Degeneration

=      Vitreous opacities, degeneration.
 
FFF: Red patch in the macula due to haemorrhage in the choroid, or choroidal vascular degeneration underlying the macula – Not common. Cystoid degeneration } Peripheral retinal degenerations
 
Lattice Degeneration  } They lead to a hole or tear in the reliance through which fluid vitreous passes under the retina leading to rhematogenous retinal detachment.
 
What are the COMPLICATIONS in MYOPIA (pathological or high myopia)?
 

(1)   Rhegmatrogeous retinal detachment

(2)   Complicated cataract.

(3)   Central visual Scotoma’s field less due  to FFF

(4)   Peripheral field less.
 
What are  the ways to diagnose?
  •      Retinoscopy – Objective method of knowing the refractive of the eye.
  •       Fundoscopy (ophthalmoscopy) to reveal other findings of myopia.
 
What is the TREATMENT OF MYOPIA ?
 

(1)   Concave lens in spectacle

(2)   Contact lens: - G.P. Lens & Soft lenses.

(3)   Surgery for myopia:
 
  • Radial keratotomy (R.K.): - 4 - 8 partial thickness, peripheral corneal incisions will weaken the peripheral cornea- leading to flattening of the central cornea. Thus myopia is reduced.
  • Epi kerato phakia (Epikeratophakia)-Concave lenticule is prepared from donor cornea. That is sutured on to the patient’s cornea after pealing off the epithelium of patients cornea.
 

(4)   Barraquer:
a.    Keratomileusis (mileus = mould, to shape)
A central part of patients own cornea is removed, put into computerized micro lathe and mould into a concave lens, put it back in its position – overlying corneal “lid” is sutured.
 
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