Laser Eye Surgery for Astigmatism — All You Need to Know

It wasn’t that long ago that we were much more limited in our ability to correct astigmatism. Even now, there are still patients who believe they are excluded from contact lens wear because of their astigmatism. And patients who understand there are now toric contacts that can correct astigmatism still think they’re ineligible for laser eye surgery because of it. However, medical technology has made significant advancements since the days when glasses were the only option for correcting astigmatic prescriptions. Keep reading to find out more about laser eye surgery for astigmatism.  

What You Should Know About Astigmatism

Astigmatism is a type of refractive error. There are two sources of astigmatism – corneal and lenticular. Corneal astigmatism makes up the majority of astigmatic cases. It occurs when the cornea, the front surface of the eye, is not regularly rounded. Instead, it may be more curved along one axis, like an AFL football. This means that light passing through the cornea is bent to different degrees, depending on the axis on which it entered the eye. Lenticular astigmatism refers to astigmatism arising from an irregular curvature of the lens inside the eyeball.

Astigmatism can be found on its own or can be in combination with short-sightedness (myopia) or long-sightedness (hyperopia). While myopia means the focal point of light falls in front of the retina and hyperopia means this point falls behind the retina, astigmatism creates two separate focal points. One or neither of these points may focus on the retina, which is what we need for sharp sight. 

Because light passing through an astigmatic cornea or lens results in two focal points, your sight is affected at all distances. Unlike myopia, where your near sight is sharp while distance vision is unclear, uncorrected astigmatism can cause the following effects at all distances:

• Blurriness
• Flaring or starbursts of lights
• Glare at night
• Ghosting or shadowing of images
• Headaches and eyestrain

Optometrists can correct astigmatism with glasses and soft or hard contact lenses. Diagnosis of astigmatism occurs during a routine eye test when an optometrist measures your prescription. It is fairly common to have some degree of astigmatism. Those interested in laser eye surgery for astigmatism can be referred to an ophthalmologist specialising in refractive surgery. 

Laser Eye Surgery for Astigmatism

Laser eye surgery techniques are based on corneal reshaping. By adjusting the curvature of the cornea, the surgeon can control how light is bent through this surface. The aim is to get light to focus on a single sharp point on the retina. 

The main laser eye surgery methods that can be used to correct astigmatism are:

• LASIK (laser-assisted in situ keratomileusis)
• PRK (photorefractive keratectomy)
• SMILE (small incision lenticule extraction)

Where LASIK and PRK are routinely used in laser eye surgery procedures for astigmatism, the application of SMILE is more limited. At the moment, SMILE can only be used to correct myopic astigmatism – that is, astigmatism in the presence of short-sightedness, up to -3 dioptres. It is not yet suitable for treating hyperopia or isolated astigmatism. LASIK and PRK laser eye surgery may correct astigmatism up to -5 dioptres.

Similar to treating myopia or hyperopia, treating astigmatism with laser eye surgery involves using a laser tool to reshape the surface. Based on your biometric measurements taken pre-operatively, the computer guides the movements of the laser to remove precise areas of corneal tissue so that light is focused evenly and accurately through the eye. 

There are some significant differences between the LASIK, PRK, and SMILE techniques, though all are considered to be safe and effective for the treatment of refractive errors. This is a brief summary of each laser eye surgery method:

• LASIK involves cutting a flap of corneal tissue from the upper layers. This flap is moved to the side so that an excimer laser can reshape the deeper layers. This process is called photoablation. After photoablation, the flap is repositioned. 
• PRK involves removing the superficial epithelial cells of the cornea in a step known as debridement. After photoablation has been performed on the remaining tissue, the epithelium is allowed to regenerate on its own. 
• SMILE is a minimally invasive technique. Unlike both LASIK and PRK, the upper layers of the cornea are left undisrupted. Instead, a femtosecond laser is used to create a disc of tissue from the inner layers of the cornea. This is also known as a lenticule. The disc is shaped in such a way that once it’s removed through a keyhole incision, the remaining corneal structure is subsequently altered in its curvature. 

Each technique comes with its own pros and cons. 

Is My Astigmatism Suitable for Laser Eye Surgery?

For each method of laser eye surgery, there are eligibility criteria to meet. In addition to ensuring your prescription, including your astigmatism, is within the treatable range for each method, your surgeon also needs to check:

• Your age is appropriate for laser surgery. Patients who are too young may be subject to further changes in their prescription as their eyes are still growing. Conversely, patients who are older and approaching presbyopia will have short-lived satisfaction from laser eye surgery.
• Your corneal thickness. As laser surgery involves the removal of corneal tissue, you must have enough to begin with. If your residual corneal tissue is too thin after surgery, it can lead to weakening and distortion.
• Your eyes are in good overall health. If you have a condition that limits your sight, such as retinal scarring, laser surgery may not be worthwhile for you. 
• You are not currently pregnant or breastfeeding. Hormonal changes during this stage of life can affect your prescription and subsequent measurements. This may result in an over or under-correction of your prescription during laser surgery.

Call us now on (03) 9070 5788 for a consultation.

Note: Any surgical or invasive procedure carries risks. Before proceeding, you should seek a second opinion from an appropriately qualified health practitioner.   

References

Astigmatism Correction Using SMILE. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6784860/#:~:text=Comparing%20with%20laser%20in%2Dsitu,correction%20of%20myopia%20and%20astigmatism.&text=Additionally%2C%20SMILE%20seems%20to%20have,eyes%20with%20a%20larger%20pupil.

Does my eyeglass prescription qualify for LASIK?
https://www.allaboutvision.com/visionsurgery/faq-prescription.htm