Understanding Refractive Errors
Laser eye surgery is designed to treat refractive errors — conditions where the eye doesn't focus light correctly on the retina. Before deciding whether laser surgery is right for you, it helps to understand exactly what condition you have, what causes it, and how the surgery addresses it at a structural level.
What Is Myopia (Nearsightedness)?
Myopia is the most common refractive error worldwide. A person with myopia can see objects up close clearly, but distant objects appear blurry. It occurs when the eyeball is slightly too long from front to back, or when the cornea is too steeply curved. As a result, light focuses in front of the retina rather than directly on it.
How Laser Surgery Corrects Myopia
The excimer laser flattens the central cornea, reducing its curvature. This moves the focal point backward so that it lands precisely on the retina. LASIK, PRK, and SMILE are all highly effective for myopia correction.
What Is Hyperopia (Farsightedness)?
Hyperopia is essentially the opposite of myopia. Distance vision may be clearer than near vision, but in moderate to severe cases, both near and distant objects can appear blurry. Hyperopia occurs when the eyeball is slightly too short or the cornea is too flat, causing light to focus behind the retina.
How Laser Surgery Corrects Hyperopia
For hyperopia, the laser steepens the peripheral cornea (rather than the center), which effectively increases the eye's focusing power. Hyperopia treatment is somewhat more complex than myopia correction, and not all laser platforms are equally effective for high degrees of farsightedness. Your surgeon will assess whether you fall within the treatable range.
What Is Astigmatism?
Astigmatism is caused by an irregularly shaped cornea or lens — instead of being perfectly round like a basketball, the eye is shaped more like a football. This uneven curvature means light refracts differently in different meridians, causing blurry or distorted vision at all distances. Astigmatism frequently occurs alongside myopia or hyperopia.
How Laser Surgery Corrects Astigmatism
The laser treats astigmatism by smoothing out the cornea's uneven curvature, creating a more uniform, spherical surface. Modern laser platforms can address both the spherical (nearsighted or farsighted) component and the cylindrical (astigmatism) component of a prescription simultaneously. LASIK and PRK both handle astigmatism well; SMILE is also approved for myopic astigmatism.
What About Presbyopia?
Presbyopia is the age-related loss of near focusing ability that typically becomes noticeable in the mid-40s. Unlike myopia, hyperopia, and astigmatism, presbyopia is caused by stiffening of the eye's natural lens — not corneal shape. Standard LASIK does not correct presbyopia, but options include:
- Monovision LASIK: One eye is corrected for distance and the other for near — the brain blends the two images. Not ideal for everyone.
- LASIK for distance + reading glasses: Many patients accept the need for readers after LASIK.
- Refractive lens exchange (RLE): Replacing the eye's natural lens with a multifocal artificial lens — typically considered for patients in their 50s and beyond.
Reading Your Prescription: A Quick Guide
| Term | What It Means |
|---|---|
| SPH (Sphere) | Degree of myopia (−) or hyperopia (+) |
| CYL (Cylinder) | Degree of astigmatism |
| AXIS | Orientation of astigmatism in degrees |
| ADD | Additional power for near vision (presbyopia) |
Does Your Prescription Fall Within Treatable Limits?
LASIK and similar procedures have defined treatable ranges approved by the FDA. If your prescription falls significantly outside those ranges — for example, very high myopia or hyperopia — your surgeon may recommend alternative procedures such as implantable collamer lenses (ICL), which sit inside the eye rather than reshaping the cornea.
The Key Takeaway
Myopia, hyperopia, and astigmatism are all structural issues related to the shape of the eye. Laser surgery addresses each by precisely reshaping the cornea so that light focuses correctly. Understanding your specific diagnosis helps you have a richer, more productive conversation with your surgeon about which procedure — and which expected outcome — is realistic for your eyes.