Hypermetropia

News4Medico

Jan 17, 2015

1643

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.