u/WavefrontRider

The most common way to talk about astigmatism is that the cornea is shaped more like an football (the American style of football) rather than a basketball. This means the cornea has two separate curves: a steep one and a flat one. This prevents light from focusing on a single point onto the retina.

So how do we make those two curves equal and thus make the cornea more basketball or spherical shaped? There are two approaches to getting rid of astigmatism. We can make the flat part steeper or the steep part flatter.

Because the lasers used in laser eye surgery are only capable of removing corneal tissue to achieve the desired refractive effect, making the flat part steeper is the easier way to go when treating nearsighted astigmatism.

To make the flat axis of astigmatism steeper, the laser does its treatment peripherally on the flat portion. It makes that area less flat and thus more steep. This is done until it steepens enough to match the steep axis of the astigmatism. Once that is achieved, the astigmatism is eliminated and the cornea has a nice spherical symmetrical shape - eliminating the blur induced by astigmatism.

20/20 is often used as a shorthand for a successful outcome after refractive surgery. But here’s the thing about “20/20”. It is actually just a population average; what a “normal” eye is expected to resolve or see at 20 ft. And in fact, many people actually see BETTER than 20/20.

So if your best corrected vision with a pair of glasses is better than 20/20 such as 20/15, you’ll may not be happy if your vision is “just” 20/20 after Lasik, PRK or ICL. The world will appear slightly out of focus compared to what you are used to. Despite having “perfect 20/20 vision”.

So 20/20 isn’t really the goal with refractive surgery. The best clinics, surgeons and plans actually aim to match or exceed what your eyes are capable of. This comes from pushing your eye to its maximum limit during the prescription refraction testing. This also comes from using modern technology such as wavefront-optimized, wavefront-guided, topography-guided or ray-tracing which can match or even improve the limit of your eyes are capable of seeing.

So really when talking about refractive surgery, it’s less important to discuss whether you will be 20/20 afterwards but instead whether the procedure can correct you or get you close to your very best possible correction.

Lingering blurriness following a refractive surgery procedure such as Lasik, PRK or SMILE very rarely is the result of any surgical complication or failure of the technology. Instead, it is almost always some residual refractive error or remaining prescription. A small amount of nearsightedness, farsightedness or astigmatism may remain after the eye has finished healing.

Today’s laser treatments are very sophisticated and accurate. However, it is impossible to have 100% accuracy when dealing with living tissue such as the cornea. There are unique factors such as your own individual biomechanical response to the treatment or the way your corneal epithelium remodels that affect the final prescription of the eye.

In addition to just being “blurry”, residual prescription often can lead to post-op eye strain and “visual fatigue” as you work harder to focus through the slight defocus. Additionally, many nighttime vision symptoms are actually caused by these lingering prescription errors as the same blur you notice during the day makes it much harder to see at night.

The good news is that residual prescription error can be fixed. Once the eye has stabilized and if there is enough corneal thickness remaining, an enhancement or touch-up procedure can take care of the remaining prescription and improve the blurriness.

It’s natural to focus on the actual corneal shape and prescription after laser eye surgery. But it is in fact the layer of tears on the surface of the cornea, called the tear film, that is first and most important refractive surface.

When this tear film is unstable, light scatters before it even reaches the cornea and lens. This causes blurry vision. But because the tear film becomes smooth immediately after blinking, this typically causes fluctuating vision where sometimes you can see well (especially right after blinking) but other times you have blurry vision.

While the corneal laser eye surgeries (Lasik, PRK and SMILE) do induce a post-operative dry eye, there are other factors at play causing this tear film instability. The most common reason is something called Meibomian Gland Dysfunction (MGD). Within the eyelid are tiny glands (the Meibomian Glands) that secrete oils onto the surface of our tear film. These oils are responsible for preventing the watery layer of tears from evaporating away. If the consistency of these oils is poor or the glands blocked or inflamed from a condition called Blepharitis, not enough oils get onto the surface of the eye and the tear film becomes unstable.

While preservative-free artificial tears are important for immediate lubrication and prevention of further development of dry eye after refractive surgery, it’s also important to treat the root cause of MGD and blepharitis. This involves treating the blepharitis with eyelid scrubs, medications or sprays and treating the MGD with warm compresses and omega-3 supplements.