A refractive error occurs when the image can’t be perfectly focused on the retina due to disturbances of the optics of the eye. The result is a blur in vision at some distance. High refractive errors can be accompanied by headaches, difficulty reading print, print jumping around, halos and glare and double vision.
While refractive errors are very common, they usually progress very slowly and often one doesn’t notice changes with vision until a considerable degree of refractive error has taken effect. R
efractive errors are non-concerning if picked up and managed early. Refractive errors are usually easily corrected with the aid of lenses prescribed by an experienced optometrist. The lenses help refocus the image, bringing it back to clear view.
Risks of Refractive Errors
- Excessive screen exposure: TV, mobile use, Tablets and laptops
- Frequent reading of small print or at very near distances
- Inadequate lighting
- Family history of wearing eyeglasses
Eye Optics:
The Cornea
The cornea is the transparent outer protective layer of the eye. It looks like a perfectly spherical half-dome. The cornea is the first point of refraction (light bending). Light rays coming from objects in our visual field cross the cornea into the lens.
The Lens
The lens is a clear flexible disc that further refracts light rays by constantly changing shape to fine tune the focus as we look at different distances.
Accomodation is the ability of the eye to efficiently change focus from a distant object to near. our ability to accommodate swiftly reduces with age.
The Retina
Retina provides a platform for the endpoint of light refraction, ideally light rays should all be focused on the retina. It is composed of photoreceptors that help convert the light rays into visual information that are delivered to the brain via the optic nerve.
How eye shape affects how you see?
There are several types of refractive errors depending on how the eye is shaped.
Types of Refractive Errors
1. Hyperopia or Far Sightedness
Hyperopia occurs because the length of the eyeball is too short causing the image to be focused behind the retina.
Hyperopia is typically present in infants and young children, as the child grows the hyperopia typically lessens towards no refractive error.
High degrees of Hyperopia can be associated with presence of amblyopia (lazy eye) or accommodative esotropia (a form of inward eye turn).
Hyperopia is usually corrected with plus lenses.
2. Myopia/ Hypermetropia or Short Sightedness
Myopia occurs because the length of the eyeball has grown too long, causing the image to be focused infront of the retina.
This is the most common form of refractive error, typically onsetting at mid teens.
Myopia is corrected with minus lenses. However, newer forms of treatment are emerging to delay or slow the progress of myopia such as Ortho-K contact lenses. Studies have also showed that children who spend more time outdoors are less likely to develop myopia due to reduced eyeball growth rate.
3. Astigmatism
Astigmatism is general blur at any distance, particularly round objects don’t seem to appear as round and sharp. At night, people tend to complain of starry halos around light. Astigmatism occurs because the perfectly spherical cornea isn’t as spherical as it should be. Depending on the way the cornea is shaped, the image can only be focus at a certain direction determined by your eye care professional. Astigmatism is corrected using cylindrical lenses.
4. Keratoconus
Keratoconus IS NOT A REFRACTIVE ERROR! However, the mechanics of it are related to the shape of the eye and it is initially managed the same way as refractive errors via the aid of lenses.
Keratoconus is a hereditary condition often starting to appear during the teen years and early adulthood. The cornea very gradually changes shape to become more cone-like.
Initially, the person may be requiring a pair of eyeglasses, possibly with a moderate to high degree of astigmatism. But the rate of eyeglass change frequency and the constant complaining of blurred vision may indicate changes consistent with keratoconus. People with keratoconus are more sensitive to light and glare and find night driving an issue.
In the early stages, Keratoconus is managed with eyeglasses and contact lenses that help control the shape of the cornea. Later stages would involve use of more rigid contact lenses. Severe cases may undergo a simple treatment of corneal collagen cross linking or may require more invasive surgeries such as corneal transplant.
5. Presbyopia
I am terribly sorry to say this, but almost all of us are going to be presbyopic at some age, as we get older. As we age, our flexible lens becomes more rigid and loses the ability to accommodate. In simpler terms, we just need a pair of readers to help us magnify near print!
Tip #1: If you don’t have an existing refractive error such as near/far sightedness or astigmatism; feel free to trial out cheap reading glasses available at the chemist. Grab a small print and see which power magnifies comfortably.
Tip #2: If you do have an existing refractive error, it’s best to have the optometrist embed the “reading power” into your existing eye glasses. This is what is referred to as multi-focal glasses. Your glasses allows you to see a range of different distances by incorporating a couple of lens powers into one.
Other Forms of Management/ Treatments
- Contact lenses instead of eyeglasses
- Ortho K to control myopia progression (while you sleep)
- Misight to control myopia progression (during the day)
- Laser surgery (LASIK/LASEK/PRK) too change the shape of cornea and refocus the images
- Intraocular lens exchange as an alternative for laser surgery in post presbyopic age patients.
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