SHARES
Did you know the eyes are the most highly developed sensory organs in the human body? In fact, the area of the brain responsible for eyesight is more extensive than for hearing, taste, touch or smell combined.
Although eyesight is crucial, the estimate is as many as 153 million people worldwide live with visual impairment due to uncorrected refractive errors. Refractive error results in blurred vision due to the inability of the eyes to focus images from the outside world. The common refractive errors are:
- Myopia (short-sightedness): Trouble in seeing distant objects clearly
- Hyperopia (long-sightedness): Trouble in seeing near objects clearly
- Astigmatism: Distorted vision resulting from an irregularly curved cornea
- Presbyopia: Trouble in reading or seeing at arm’s length due to aging
It may impossible to prevent refractive errors. Nevertheless, regular eye examination allows diagnosis and correction of eyesight problems. Correction is recommended according to eye defect, age of the person and functional requirements. The eyesight can be corrected with corrective glasses, contact lenses or refractive surgery. Corrective glasses come with single-vision lenses, bifocal lenses or varifocal lenses.
Single-vision Lenses
Single-vision lens has one prescription that covers the whole lens. It is usually for people with long or short sight who need glasses to help them see better. For instance, someone short sight would need glasses to see far objects clearly, and vice versa.
This lens type is commonly worn by the younger crowd because they are more likely to have only one prescription. However, as other eyesight problems appear later in life, another pair of glasses might be necessary for different tasks.
Bifocal Lenses
Bifocal lenses are combination of two pairs of single-vision lenses into one. Typically, the upper half of the lens is for distance vision (to see far objects); meanwhile, the lower part is for near vision (to see near objects).
Shapes of lens segment to correct near vision (Source: Specsavers)
When most people enter their forties, reading or focusing on near objects can become more difficult. This normal part of aging is known as presbyopia. An eye check-up may be necessary when you find yourself holding your phone further away to see clearly. If you already wear glasses, perhaps it is time to consider bifocal lenses; meanwhile, a single-vision lens for near vision might be helpful for someone who had never worn glasses before.
Varifocal Lenses
Varifocal lenses, also known as progressive lenses, accommodate for near and distant vision, and everything else in between. These lenses feature gradual change in strength from the top to the bottom of the lens: The upper part for distant vision, the middle part for intermediate ranges (eg. computer work) and the lower part for near vision. Hence, moving your head and eyes would allow you to assess different parts of the lens to see objects of various distance.
Looking through a varifocal lens
Although both bifocals and varifocals can correct presbyopia, varifocals may be a better option, albeit more expensive. Unlike bifocals, varifocals do not come with dividing lines within the lens. Thus, the lens would look more cosmetically pleasing and more appealing to those who would like to disguise presbyopia.
Bifocal lens vs progressive lens
Conclusion
Refractive error is an eye condition that is easily correctable by a good pair of glasses. Regular eye check-up would allow corrections to be made as soon as possible. If you or your loved ones experience blurry vision, consult an optometrist.
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by Joanne Lee
Multipotentialite. Loves creating and seeing ideas come alive. View all articles by Joanne Lee.
