Soft contact lenses first came about in the 1960s, but in these early days many patients found themselves excluded as contact lenses for astigmatism were not yet invented.
Astigmatism refers to, in most cases, an irregularly shaped cornea, which results in light focusing through this surface to fall on two different points.
A popular analogy to explain astigmatism is to describe the cornea as being shaped more like the curvature of an AFL football, which differs depending on whether you follow the curve sideways or lengthways, as opposed to a soccer ball which is the same curvature no matter which direction you follow its surface.
While most cases of astigmatism arise from the cornea at the front surface of the eye, some astigmatism may also result from the lens inside the eye, known as lenticular astigmatism. Uncorrected astigmatism may cause:
- Blurry vision
- A starburst-type glare of lights, such as oncoming car headlights at night
- Headaches and eyestrain
- Ghosting or shadowing of images
How do Contact Lenses for Astigmatism Work?
As medical technology developed, so did techniques and materials used to create contact lenses. We continue to make advancements in materials that are more hydrated and oxygen permeable for better comfort and health of the eye. We now also have contact lens options that can correct for a much wider range of parameters and prescriptions – including astigmatism.
In the late 1970s contact lenses for astigmatism, also known as toric lenses, became available.
As astigmatism is defined by a power along a certain axis across the eye’s surface, contact lenses for astigmatism need to be consistent in their placement on the eye in order to properly align their correction with the axis of the astigmatism.
A poorly fitted toric contact lens is unstable on the eye between blinks or eye movements, constantly throwing the astigmatic correction of the lens off axis. This results in fluctuating vision and, depending on the magnitude of the rotation and the degree of astigmatism, can be intolerable.
Ensuring a contact lens for astigmatism remains aligned on the eye is a concept known as stabilisation.
Different manufacturers achieve this in different ways but all work on the basic principle of varying lens thickness (and therefore weight) across different zones of the lens, taking advantage of gravity to orientate the lens a specific way on the eye.
Toric contacts also tend to be slightly wider in diameter to assist in stability.
However, because eyelid anatomy and the dynamics of blinking and eye movements vary from individual to individual, one toric lens that fits well on one eye will not necessarily fit well on the next.
Some patients with astigmatism may be frustrated to find that they simply cannot achieve adequate vision with contact lenses.
Intraocular Contact Lenses
Intraocular contact lenses, also known as implantable contact lenses, are a biosynthetic collagen lens designed to be surgically inserted inside the eye, placed between the iris (the coloured part of the eye) and the natural lens of the eye.
A small incision is made in the cornea for the lens to be inserted. Because very little tissue is disrupted during the procedure and the lens can be easily removed if not well tolerated, intraocular contact lenses are considered to be a safe and effective method of permanent vision correction.
The procedure itself is quick and recovery times short, but the greatest advantage of implantable contact lenses is the vast range of prescriptions it can cover.
Options in regular contact lenses are scarce once exceeding around -2.75 dioptres of astigmatism, and the few toric lenses available past this degree may have a greater likelihood of being unsuitable for an astigmatic patient. However, implantable contact lenses can treat astigmatism of up to -4.5 dioptres, myopia of up to -18 dioptres, and hyperopia of up to +8 dioptres.
As the lens sits within the eye, it is not subject to the dynamics of eyelid movement and difficulties of stabilisation, making it an excellent option for vision correction in patients who are unsuccessful with toric contact lenses while wishing to reduce dependency on spectacles.
Intraocular contact lenses are often also a viable option for patients looking into refractive surgery but find themselves falling outside of the parameters for LASIK or PRK. Unlike these procedures, implantable contact lenses do not rely on minimum corneal thickness in order to provide correction of the prescription.
Astigmatism doesn’t need to exclude you from being spectacle-free. See your local optometrist for your options in toric contact lens fitting, or for those who wish to rid themselves of both glasses and contacts, book your complimentary initial consultation with Eye Laser Specialists today. Call us at 1300 297 583