Hypermetropia

Hypermetropia

Etiology

Axial hypermetropia

·         By far the commonest form in which the total refractive power of the eye is normal but axial length is short

·         About 1mm shortening of the anteroposterior diameter of the eye results in 3 diopters of hypermetropia

Curvatural hypermetropia

·         Is the condition  in which the curvature of the cornea, lens, or both is flatter than normal, resulting in a decrease in the refractive power of the eye

·         About 1mm increase in radius of curvature results in 6 diopters of hypermetropia

Index hypermetropia

·         Occurs due to changes in the 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 congenital or acquired (following surgical removal or posterior dislocation) leads of aphakia

Clinical types

Simple Hypermetropia

·         Results from normal biological variants 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

Senile hypermetropia / acquired hypermetropia

occurs in old age due to two causes –

1) curvatural hypermetropia

2) index hypermetropia

Positional hypermetropia may occur due to posterior subluxation of lens

Aphakia due to either congenital or acquired (following surgical removal or posterior dislocation)

Consecutive hypermetropia due to surgically overcorrected myopia or pseudophakia with undercorrection

Clinical types

Functional Hypermetropia results from paralysis of accommodation as seen in patients with third nerve palsy and internal ophthalmoplegia

Components of hypermetropia

Total hypermetropia

Total amount of refractive error which is estimated after complete cycloplegia with atropine

Latent hypermetropia

·         Implies the amount of hypermetropia (about 1D) which is normally corrected by inherent tone of ciliary muscle

·         The degree of latent hypermetropia is high in children and gradually decreases with age

·         Latent hypermetropia disclosed when refraction is carried after abolishing the tone with atropine

Components of hypermetropia

Manifest hypermetropia is the remaining portion of hypermetropia which is not corrected by the ciliary tone

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 can not be corrected by the patient’s accommodative effort

Symptoms

·         Asymptomatic

·         Asthenopic symptoms

·         Defective vision with asthenopic symptoms

·         Defective vision with out asthenopic symptoms

·         The effect of ageing on vision

·         Intermittent sudden blurring of vision

·         Crossed eye sensation

Signs

·         Size of eyeball may appear small

·         Cornea may be slightly smaller than normal

·         Anterior chamber is comparatively shallow and angle is narrow

·         Visual acuity varies with the degree of hypermetropia

·         Fundus examination

Ø  small optic disc which may look more vascular with ill-defined margins

Ø  Pseudo papillitis

Ø  Shot silk appearance

·         A – scan unltrasonograpy may reveal a short axial length

Complications

·         Recurrent styes, blepharitis or chalazion may occur. Probably due to infection introduced by repeated rubbing of eyes

·         Accommodative convergent squint may develop in childen due to excessive use of accommodation

·         Amblyopia may develop in some cases, may be anisometropic, strabismic or ametropic

·         Predisposition to develop primary narrow angle glaucoma

Treatment

·         Total amount of hypermetropia should always be discovered by performing refraction under complete cycloplegia

·         If the total manifest refractive error is small, correction is given only if the patient is symptomatic

·         Gradually increase the spherical correction at 6 months interval till the patient accepts manifest hypermetropia

·         If there is associated exophoria, the hyperopia should be under corrected by 1 to 2 D

·         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

·         It is important to remember that in children hypermetropia may diminish with the growth of the child. So refraction should be carried out every six months and if necessary the correction should be reduced

There are several optical and surgical treatment options available for hypermetropia:

Optical treatment:

Spectacle: Corrective lenses, including eyeglasses, are the most common way to correct hypermetropia. The lenses are designed to bend the light entering the eye so that it focuses correctly on the retina.

Contact lenses: Like eyeglasses, contact lenses can also correct hypermetropia. They are placed directly on the eye and work by changing the way that light enters the eye.

Surgical treatment:

LASIK: Laser-assisted in-situ keratomileusis (LASIK) is a surgical procedure that uses a laser to reshape the cornea. This changes the way that light enters the eye, correcting hypermetropia.

PRK: Photorefractive keratectomy (PRK) is similar to LASIK but does not involve creating a flap in the cornea. Instead, the outer layer of the cornea is removed, and a laser is used to reshape the underlying tissue.

LASEK: Laser epithelial keratomileusis (LASEK) is similar to PRK but involves preserving a thin layer of the cornea's outer layer (epithelium) to aid in healing.

Phakic intraocular lenses (IOLs): Phakic IOLs are artificial lenses that are surgically implanted into the eye. They are designed to correct refractive errors and can be used to correct hypermetropia.

Clear lens exchange (CLE): CLE is a procedure in which the natural lens of the eye is removed and replaced with an artificial lens that corrects refractive errors. This can be used to correct hypermetropia, particularly in people who are not good candidates for LASIK or other laser-based procedures.