Myopia (short-sightedness) is a characterised by blurred distance vision. The blurred vision is caused by the eyeball being too long or the front of the eye (the cornea) being too curved for distant objects to be focused exactly at the back of the eye. Difficulty reading road signs or subtitles on television or difficutly recognising faces at a distance may all be symptoms of uncorrected myopia. Myopia can be corrected with glasses, contact lenses, orthokeratology and refractive surgery.
Hyperopia ( hypermetropia or long-sightedness) is characterised by excessive focusing effort . Either the eyeball is too short or the cornea is too flat for objects to be focused exactly at the back of the eye. This may result in blurred vision, particularly at close distances. Unlike myopia, focusing effort can eliminate the blur. This focusing effort can be difficult to sustain for long periods and can result in feelings of eye stain and tiredness. The lens inside the human eye loses its flexibility with age, and the focusing problem effort associated with hyperopia becomes more difficult. Older hyperopes are more likely to need correcting devices than younger ones. Hyperopia can be corrected with glasses, contact lenses, orthokeratology and refractive surgery.
Astigmatism is a condition in which the front of the eye (the cornea) isn’t perfectly round and this reults in blurred vision. Astigmatism can be regular or irregular. Regular astigmatism is able to be corrected with glasses, contact lenses, orthokeratology and refractive surgery.
Irregular astigmatism can be caused by conditions like keratoconus or corneal scarring and is usually not well corrected with spectacles or soft contact lenses Rigid gas permbeable lenses are the ideal option and correct the blurred vision by covering the irregular cornea with a smooth and regular surface. The tears behind the lens fill the irregularity and a clear and regular image results
Presbyopia is the age-related loss of close focusing ability, caused by the lens inside the eye losing its flexibility. Initial signs are difficulty reading small print especially in poorlight. Nearly everyone will require assistance with close tasks as they get older. This process is not influenced by myopia, hyperopia or astigmatism but the impact it has may be lessened or worsened by those conditions. Presbyopia can be corrected with glasses, contact lenses, orthokeratology and refractive surgery. The correction process must take into account both close focusng difficulties and any underlying refractive error.