Hypermetropia

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  • HYPERMETROPIA
    • Hypermetropia (hyperopia) or long-sightedness is the refractive state of the eye wherein parallel rays of light coming from infinity are focused behind the retina with accommodation being at rest
    • Thus, the posterior focal point is behind the retina, which therefore receives a blurred image.
  • Etiology
    • Axial hypermetropia
      • Commonest form.
      • In this condition the total refractive power of eye is normal but there is an axial shortening of eyeball.
      • About 1–mm shortening of the antero- posterior diameter of the eye results in 3 dioptres of hypermetropia.
    • Curvatural hypermetropia
      • condition in which the curvature of cornea, lens or both is flatter than the normal results in a decrease in the refractive power of eye.
      • About 1 mm increase in radius of curvature results in 6 dioptres of hypermetropia.
    • Index hypermetropia
      • occurs due to decrease in refractive index of the lens in old age.
      • It may also occur in diabetics under treatment.
    • Positional hypermetropia results from posteriorly placed crystalline lens.
    • Absence of crystalline lens
      • either congenitally or acquired (following surgical removal or posterior dislocation) leads to aphakia — a condition of high hypermetropia.
  • Clinical types
    • Simple or developmental hypermetropia
      • commonest form
      • results from normal biological variations in the development of eyeball.
      • It includes axial and curvatural hypermetropia.
    • Pathological hypermetropia
      • results due to either congenital or acquired conditions of the eyeball which are outside the normal biological variations of the development.
        • Index hypermetropia (due to acquired cortical sclerosis),
        • Positional hypermetropia (due to posterior subluxation of lens),
        • phakia (congenital or acquired absence of lens)
        • Consecutive hypermetropia (due to surgically over-corrected myopia).
    • Functional hypermetropia
      • results from paralysis of accommodation
      • seen in patients with third nerve paralysis and internal ophthalmoplegia.
    • Total hypermetropia = latent + manifest (facultative + absolute).
      • Total hypermetropia
        • total amount of refractive error, which is estimated after complete cycloplegia with atropine
        • It consists of latent and manifest hypermetropia.
      • Latent hypermetropia
        • amount of hypermetropia (about 1D) which is normally corrected by the inherent tone of ciliary muscle.
        • The degree of latent hypermetropia is high in children and gradually decreases with age.
        • The latent hypermetropia is disclosed when refraction is carried after abolishing the tone with atropine.
      • Manifest hypermetropia i
        • remaining portion of total hypermetropia, which is not corrected by the ciliary tone.
        • It consists of two components, the facultative and the absolute hypermetropia.
          • Facultative hypermetropia constitutes that part which can be corrected by the patient’s accommodative effort.
          • Absolute hypermetropia is the residual part of manifest hypermetropia which cannot be corrected by the patient’s accommodative efforts.
  • Clinical picture
    • Symptoms
      • Asymptomatic.
        • A small amount of refractive error in young patients can be asymptomatic
      • Asthenopic symptoms.
        • Occur even when the amount of hypermetropia is fully corrected
        • Occur due to sustained accommodative efforts patient develops asthenopic symptoms.
        • These include
          • tiredness of eyes
          • frontal or fronto-temporal headache
          • watering
          • mild photophobia.
        • associated with near work
        • increase towards evening.
      • Defective vision with asthenopic symptoms.
        • Occur when the amount of hypermetropia is such that it is not fully corrected by the voluntary accommodative efforts
      • Defective vision only.
        • When the amount of hypermetropia is very high, the patients usually do not accommodate (especially adults) and there occurs marked defective vision for near and distance.
    • Signs
      • Size of eyeball may appear small as a whole.
      • Cornea may be slightly smaller than the normal.
      • Anterior chamber is comparatively shallow.
      • Fundus examination reveals
        • a small optic disc
          • which may look more vascular with ill-defined margins
          • simulate papillitis (though there is no swelling of the disc, and so it is called pseudopapillitis).
        • The retina as a whole may shine due to greater brilliance of light reflections (shot silk appearance).
      • A-scan ultrasonography (biometry) may reveal a short antero-posterior length of the eyeball.
  • Complications
    • Recurrent styes, blepharitis or chalazia
      • occur due to infection introduced by repeated rubbing of the eyes, which is often done to get relief from fatigue and tiredness.
    • Accommodative convergent squint may develop in children (usually by the age of 2-3 years) due to excessive use of accommodation.
    • Amblyopia may develop in some cases.
      • anisometropic (in unilateral hypermetropia)
      • strabismic (in children developing accommodative squint)
      • ametropic (seen in children with uncorrected bilateral high hypermetropia).
    • Predisposition to develop primary narrow angle glaucoma.
      • The eye in hypermetropes is small with a comparatively shallow anterior chamber. Due to regular increase in the size of the lens with increasing age, these eyes become prone to an attack of narrow angle glaucoma.
      • This point should be kept in mind while instilling mydriatics in elderly hypermetropes.
  • Treatment
    • Optical treatment
      • prescribe convex (plus) lenses, so that the light rays are brought to focus on the retina
      • Fundamental rules for prescribing glasses in hypermetropia include:
        • Total amount of hypermetropia should always be discovered by performing refraction under complete cycloplegia.
        • The spherical correction given should be comfortably acceptable to the patient. However, the astigmatism should be fully corrected.
        • Gradually increase the spherical correction at 6 months interval till the patient accepts manifest hypermetropia.
        • In the presence of accommodative convergent squint, full correction should be given at the first sitting.
        • If there is associated amblyopia, full correction with occlusion therapy should be started.
      • Modes of prescription of convex lenses
        • Spectacles are most comfortable, safe and easy method of correcting hypermetropia.
        • Contact lenses are indicated in unilateral hypermetropia (anisometropia).
  • Refractive surgery for hyperopia
    • It should be performed after 20 years of age.
    • In general, refractive surgery for hyperopia is not as effective or reliable as for myopia.
    • Holmium laser thermoplasty
      • used for low degree of hyperopia.
      • laser spots are applied in a ring at the periphery to produce central steepening
      • Regression effect and induced astigmatism are the main problems.
    • Hyperopic PRK
      • Done using excimer laser
      • Regression effect and prolonged epithelial healing are the main problems encountered.
    • Hyperopic LASIK
      • effective in correcting hypermetropia upto +4D.
    • Conductive keratoplasty (CK)
      • nonablative and nonincisional procedure
      • cornea is steepened by collagen shrinkage through the radiofrequency energy
      • This technique is effective for correcting hyperopia of upto 3D.

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