Options to treat astigmatism
What is astigmatism?
Astigmatism, also commonly known as ‘astig’ or ‘san guang’ (in Chinese) is a type of refractive error. What exactly is a refractive error? To answer that, we must first understand what happens to light when it enters an eye that has no refractive error. Imagine our retina (the back part of our eye) as a screen on which a projector projects an image onto. When light enters our eye, it falls onto this ‘screen’ which in turn sends the image to our brain for interpretation. For the image to be projected as clear, the light must be well-focused onto the screen.
In an eye with no refractive error, the image that falls on the retina is well-focused and sharp. On the other hand, in an eye with refractive error, the image that falls on the retina is out of focused and blurry. As such, optical aids such as glasses or contact lenses are required to help bend the light as it enters the eye, allowing it to correctly focus on the retina and thereby help us to see clearly. Other types of refractive errors include myopia (short-sightedness), hyperopia (long-sightedness) and presbyopia (‘lao hua’ in Chinese).
Some symptoms one may notice with uncorrected astigmatism may include:
- Blurred or distorted vision
- Eye strain or discomfort
- Difficulty with night vision
In people with severe astigmatism, a condition known as keratoconus may be present. Keratoconus is a progressive eye disease whereby the cornea (transparent front part of the eye), which is normally round starts to bulge into a cone-like shape. People with late stage keratoconus may not benefit much from traditional optical aids such as glasses or soft contact lenses. Rather, hard contact lenses and hybrid contact lenses are required. In the worst case scenario, a cornea transplant may be required.
How would I know if I have astigmatism?
A simple screening at the GP or an optical shop will ascertain if one has astigmatism. However, should one has higher levels of astigmatism or a big difference in astigmatism between 2 eyes, it is recommended to see an eye doctor to rule out keratoconus.
For people with high astigmatism, do not wait till the occurrence of symptoms like blurriness or headaches before seeking medical help. It is advisable to visit an eye doctor yearly to have the eyes check to ensure all is well, akin to how one would visit the dentist yearly or more frequently to maintain good oral health. During your visit to the eye doctor, a test called manifest refraction will be performed by the optometrist to check for refractive errors. Should there be concerns on keratoconus, a corneal topography can be done.
How do I correct my astigmatism so I can see well?
There are broadly 2 types of solutions – non-surgical and surgical.
Non-surgical solutions are more common, and they include glasses or contact lenses (soft and rigid gas permeable hard). Another type of hard contact lenses that are used by some is known as Ortho-K lenses, which are worn to bed at night. During sleep, these lenses change the shape of the corneas, akin to how a retainer works with teeth. In the day, the lenses are removed, and the user can see clearly without glasses and contact lenses. However, this change is not permanent. Once lens wear is ceased, the corneas return to their original shape. As such, the user must be consistent and disciplined in using the lenses every night before bed. Observing high levels of hygiene is important when using Ortho-K lenses to minimise the risk of infection especially when they are worn to sleep. It is imperative for user to attend frequent follow-ups with their optometrist when using Ortho-K lenses. Suitability is dependent on the level of eye prescription and the curvature of the corneas.
Surgical methods include laser vision correction (LVC) and implantable contact lenses (ICL). LVC (ReLEx SMILE, LASIK and PRK) is performed by using a laser to sculpt the cornea to effect a permanent change in corneal shape, so glasses or contact lenses are not needed to see well. The suitability of one’s eyes for LVC is dependent on a few factors including levels of eye prescription, shape of the eyes and corneal thickness. Candidates will need to undergo a pre-laser evaluation, which includes pupil dilation and consultation with the eye surgeon to ascertain suitability and as well weigh the benefits vs risks. ICL is another surgical method whereby a collamer lens is placed into the eye, between the natural lens and iris, allowing one to see without glasses or contact lenses. This method is suitable for candidates with high refractive errors, or thin corneas. Unlike LVC, ICL is reversible whereby the lens can be removed at anytime when needed, for example, in the case of a future cataract surgery.
What if I have keratoconus due to high levels of astigmatism?
The first step when dealing with any eye diseases is not to panic or lose hope. First, it is important to have a good understanding on what the condition is and what you need to be aware of. Keratoconus usually develops in one’s 20s and is a progressive condition which usually stabilises by about 40. As keratoconus is progressive, it is vitally important to work closely with your eye doctor to monitor progression.
In early stages, vision is correctable with glasses and soft contact lenses. As it progresses, one may move to hard contact lenses or hybrid lenses to help with vision. In late or advanced stages, one may require a corneal transplant.
Collagen cross-linking (CXL) is a surgical procedure for keratoconus, aiming to stabilise the cornea. While CXL does not reverse the effect of keratoconus, it works by slowing down its progression to avoid the need for a corneal transplant in the future.
In CXL, Vitamin B2 is instilled on the eye and ultraviolet light from a special machine is shone to allow cross-linking to occur. Cross-linking simply means bonds are created between the collagen fibres within the cornea thus strengthening it.