Hypermetropia is a condition that usually begins in childhood and lasts throughout a person’s life. It is a condition where the eye has developed a focussing mechanism that is too weak at the front of the eye or if the eyeball itself is too short from front to back for the light to be focussed in the correct position on the retina.
Depending on the degree of the hypermetropia, people with this condition may be able to see clearly at all distances but may have difficulty seeing near objects with clarity and comfort. Often the earliest symptoms of hypermetropia are not necessarily near blur, but often sore, red or itchy eyes (asthenopia), headaches or distance blur, especially after reading, prolonged computer or close work.
The amount of correction required for hypermetropes depends on the extent to which the focussing mechanism is too weak for the length of the eye. For example, most people require about 60 units of refractive power (called dioptres) in the total eye for them to be able to see objects in the distance with perfect clarity and comfort. However if a person has 57 units of power instead of the required 60 units, their vision is deficient by three units and their refractive error is said to be +3.00D (“plus three dioptres”). Depending on age, this person would probably need correction fairly constantly to see with clarity and comfort, especially when performing close up tasks like reading.
A person with 59 units of power instead of the required 60 has a refractive error of +1.00D. Depending on age, this person may be able to function quite normally in the visual world but would probably benefit from a correction for sustained close up visual tasks.
A person with 55 units of power instead of the required 60 has a refractive error of +5.00D.
This person would usually require their correction all the time, as vision without correction would usually be quite blurred with much eyestrain.
The nature of the focussing mechanism of the eye allows some hypermetropia to be overcome in young people, due to the flexibility of the crystalline lens. When a young eye has a lens that is still flexible, change in the power of the lens (accommodation) may allow clear vision without blur despite the imbalance in focussing power and the length of the eye. People with hypermetropia that are coping well without correction are known as latent hypermetropes.
There has been less research into what actually causes hypermetropia than there has for myopia. Unlike myopia which can progress in response to the way it is corrected, hypermetropia seems to be fairly constant in a person’s life. What does change is the ability of the eye to keep things in focus as the crystalline lens inside the eye hardens with age.
There are various ways to correct long-sightedness. The traditional forms of correction, spectacles and especially contact lenses (or often a combination of spectacles for some occasions and contact lenses for other occasions) are still the main ways of correcting this condition although small amounts of hypermetropia can be corrected by the newer technologies made possible through orthokeratology and laser refractive surgery. All forms of correction have their advantages and disadvantages, which our optometrist at Vision Excellence at Norwest will discuss with you after carefully measuring the refractive error caused by your hypermetropia.
In later life, hypermetropia actually causes more difficulty when combined with presbyopia. For this reason, an older person who is about to have cataract surgery should discuss post-operation outcomes with their surgeon before having the procedure. It may be possible to reduce the amount of hypermetropia during the operation.