Hypermetropia

 Hypermetropia is an error of refraction in which parallel rays of light from infinity come to a focus behind the retina when accommodation is at rest.

Accommodation eye

 Parallel rays are brought to focus on the retina, by the normal lens in the eye becoming more complex. This is called accommodation.

Hypermetropic eye 

Parallel rays of light are brought to focus upon the retina, by increasing the refractivity with a convex spectacle lens. The degree of hypermetropia is given by the power of the correcting lens.

Types of hypermetropia

1. Axial hypermetropia 
2. Curvature hypermetropia 
3. Index hypermetropia 

1. Axial hypermetropia: Axial hypermetropia When the anterior/posterior length of the eyeball is shorter than normal. (Normal axial length is 24mm). A decrease of 1mm in axial length produces a hypermetropia of 3.0D. 

** all newborns are almost hypermetropic approximately +2.5D. This is due to the shortness of the globe and is physiological.

** it may also occur pathologically when the retina is displaced forward {RD, CSR, ORBITAL TUMORS, RETINAL TUMOR}

** In micro or nano ophthalmos where the axial length is less than 20.0 mm there is high hypermetropic.

2. Curvature hypermetropia: Curvature hypermetropia When the curvature of the cornea or lens is flatter than normal. An increase of 1mm in its radius of curvature produces a hypermetropia of 6.OD. 

3. Removal of the lens.aphakia

4. Index hypermetropia: Index hypermetropia When the refractive index of the media is less than normal 

- Corneal refractive index - 1.37 

- Refractive index of the cortex of lens - 1.38 

- Refractive index of the nucleus of lens - 1.40 

• Clinical types of hypermetropia 

1. Congenital hypermetropia 

2. Simple or developmental hypermetropia 

3. Acquired hypermetropia

1. Congenital hypermetropia: This is rare. It is usually associated with other congenital anomalies of the eyeball like microphthalmos. 
2. Simple or development hypermetropia: It is the most common type. A newborn baby is hypermetropic but with age, the eyeball grows in size and the hypermetropia are gradually diminished. If the growth of the eyeball is retarded then hypermetropia persists.
3. Acquired hypermetropia This is found in aphakic conditions, commonly following extraction of the lens. This hypermetropia is usually high about + 10.0 D.

*** Depending on clinical presentation hypermetropia can be of different types: 

1. Simple hypermetropia: This is due to normal biological variation in development of eyeball. This is the most common type of hypermetropia. 

2. Pathological hypermetropia: This is due to certain factors which are not in the normal biological variations, e.g. posterior subluxation of lens (positional hypermetropia), acquired cortical sclerosis (index hypermetropia), under-correction of refractive error (consecutive hypermetropia) and congenital absence of the lens (aphakia). 

3. Functional hypermetropia: It results due to paralysis of accommodation, e.g. third nerve paralysis.

***The hypermetropia which is seen after complete paralysis of accommodation, after the application of atropine TH=MH+LH 

Latent hypermetropia: It is the amount of hypermetropia which is corrected by the normal physiological tone of the ciliary muscle. It is strong at a young age and slowly declines with age. 

Manifest hypermetropia: The remaining portion which is not corrected by the normal physiological tone of the ciliary muscle is called manifest hypermetropia. It is hypermetropia that remains uncorrected in normal circumstances. That is when accommodation is not being actively used, or, in other words, it is the total hypermetropia minus the latent hypermetropia. 

This manifest hypermetropia is again made of two components. 

1. Facultative hypermetropia 

2. Absolute hypermetropia 

1. Facultative hypermetropia: It the part of hypermetropia, which can be corrected by an additional effort of accommodation or excessive the strain of the ciliary muscle. 

2. Absolute hypermetropia: Absolute hypermetropia is the part of hypermetropia which cannot be overcome by active exertion of accommodation. 

Symptoms of hypermetropia 

1. Headache 

2. Eyestrain 

3. Distance blurred vision 

4. Difficulty in doing prolonged close work 

Treatment of hypermetropia 

1. By prescribing correct convex lenses 

2. Contact lenses 

3. Lasik

***Complication of hypermetropia: Uncorrected hypermetropia leads to esophoria, which later on may develop into esotropia. convergent squint

hypermetropia with esophoria - To give full correction 

Hyperopia with exophoria - To give under e under correction

Hypermetropic individuals often have a shallow anterior chambers. They have an increased predisposition to develop narrow-angle glaucoma.

• Lid diseases: Repeated rubbing of eyes in hypermetropic blurred vision may produce blepharitis, stye, or chalazion.

amblyopia- anisometropic, strabismic,ametropic

Clinical Features of Hypermetropia

 Symptoms depend on the amount of hypermetropia and the age of the person. These may be: 

1. Asymptomatic: A person who does not have much visual requirement and has a small refractive error may not complain of any problem and refractive error may be detected just by chance. 

2. Eyestrain: Patient complains of headache, watering, tiredness of eyes while working on computer, watching television and doing reading and writing work. This is due to sustained accommodative effort. 3. Defective vision: When the amount of error is very high; the patient may not try to compensate for it and complains of defective vision. If the patient can compensate for some amount of error by accommodative effort and the rest of the error remains uncompensated; he may complain of eyestrain symptoms and defective vision both more for near than for distance. 

4. On examination size of the eyeball appears smaller with a small cornea, shallow anterior chamber, and small optic disk with indistinct margins (Pseudopapillitis). Retina shows more shining called ‘Shot Silk Retina’. Axial length can be confirmed with A-Scan.