Refractive disorders Flashcards
What is emmetropia?
Vision with no refractive error and requires no correction
What is myopia?
Term used to define short-sightedness - nearby objects are seen clearly but distant ones are blurred because light from a distant object forms an image before reaching the retina.
What might cause myopia? (3)
The eye may be too long
Cornea may be too strong
Crystalline lens may be too strong
How do you correct myopia?
Concave or negative lens
What is hypermetropia?
Term used to define long-sightedness - faraway objects are seen clearly but close ones are blurred because light from a close object forms an image beyond the retina
What might cause hypermetropia?
Eye might be too short
Cornea does not refract enough
Crystalline lens does not refract enough
How do you correct hypermetropia?
Convex or positive lens
What is astigmatism?
Presence of more than one point of focus which occurs when the cornea or crystalline lens is not spherical
What is the difference between regular and irregular astigmatism?
Regular: the peripheral medians are perpendicular
Irregular: peripheral medians are not perpendicular
How do you correct a regular astigmatism?
Toric lens
What might cause an irregular astigmatism?
Corneal scar
Scattering in the crystalline lens
How do you correct an irregular astigmatism?
Contact lenses
Laser eye surgery
What is presbyopia?
Normal ageing process of the lens where it loses elasticity so it is difficult to focus at close ranges
When does presbyopia start occurring?
Starts between 35-40 yrs of age, becomes more significant between 40-45 years.
How do you correct presbyopia
Glasses or contact lenses
Combination of options including varifocals, bi-focals, separate glasses or mono-vision for contact lenses
