Light rays enter the eye through the cornea (the clear window in front), pass through the pupil (the central opening in the iris), and are then focused through the lens before reaching the retina at the back of the eye. The retina is analogous to the film of a camera. When light rays land on the retina, they form an inverted image. The retina transforms this image into impulses that travel along the optic nerves to the brain, where they are translated into upright visual images.
Vision is clear only if the cornea and lens correctly bend or "refract" light rays, focuing them precisely on the retina's point called the fovea. In the normal eye, the cornea's focusing power aligns with the eye's length Blurry vision may be due to a "refractive error", indicating a failure of the cornea and lens to properly focus light. Prescription eye glasses, contact lenses and refractive surgery correct are used to correct or reduce refractive errors by focusing light rays closer to or directly onto the retina.
Watch the video to learn about the causes and treatments of myopia, hyperopia and presbyopia:
Myopia arises when the cornea is excessively curved (focusing power is too high) or the eyeball is too long. This causes images of distant objects to be focused in front of the retina instead of on it. The resultant blurred image on the retina is due to the spreading apart of light rays after passing the focal point.
Singapore has one of the highest rates of myopia in the world, with an estimated 28% of Primary 1 students, 65% of Primary 6 students and 80 %of young adults experiencing myopia.
To learn more about myopia in children and the treatment options, please refer to Myopia Management For Children. Read the Paediatric Cataract for Children here.
Astigmatism is a refractive error characterized by the irregular curvature of the cornea, which may be more pronounced in one direction, resembling the shape of a rugby ball or the back of a spoon. This irregularity prevents light rays from converging to a single focal point, leading to a blurred image dispersed over multiple points.
Astigmatism frequently coexists with near-sightedness or far-sightedness.
This condition arises when the cornea of the eye is insufficiently curved (resulting in a lower focusing power) or when the eyeball is too short. This combination leads to the focal point falling behind the retina, causing a blurred image as light rays haven't yet converged when reaching the retina.
Presbyopia can also be treated with either LASIK or PRK. One eye can be corrected to see far and the other eye corrected to see near. A technique known as monovision corrects one eye for distance vision and the other for near vision, eliminating the need for glasses or contact lenses. This adjustment is easily adapted by the brain within one to two weeks, and there are no issues with activities like driving or playing sports. The blending of vision between the two eyes can be further enhanced using aspherical treatment to increase the depth of focus of both eyes.
(Learn more about the different refractive surgery treatments at NUH LASIK
Low vision refers to visual impairment that cannot be corrected with standard glasses, contact lenses, medical treatment or surgery. Individuals with low vision experience severely reduced visual acuity, contrast sensitivity and/or significantly obstructed field of view.
Low vision may affect daily activities such as recognising faces, reading small prints and large signs, identifying obstacles and reduced independent mobility.
