Laser eye surgery, which includes procedures like LASIK and PRK, is a common method for correcting refractive errors such as nearsightedness, farsightedness, and astigmatism. This procedure aims to reshape the cornea, the clear front surface of the eye, to adjust how light is focused onto the retina, reducing or eliminating the need for glasses or contact lenses. While successful for millions of people, it is not a suitable option for everyone. Determining candidacy involves a thorough evaluation of a person’s general health, specific eye health, and vision parameters.
Foundational Eligibility Criteria
A person must meet several general health and vision requirements before being considered for laser eye surgery. The minimum age requirement is typically 18 years old, as prescriptions can fluctuate significantly during the teenage years. Surgeons often prefer candidates to be in their early twenties to ensure the eyes have reached full maturity, which provides a more predictable result.
A stable vision prescription is a fundamental requirement, meaning the prescription should not have changed by more than 0.5 diopters for at least 12 months prior to the procedure. General systemic health is also a factor, as uncontrolled medical conditions can impair the body’s ability to heal after surgery. Conditions such as uncontrolled diabetes or certain autoimmune disorders, like rheumatoid arthritis or lupus, can increase the risk of infection and irregular healing and may temporarily disqualify a candidate.
Temporary hormonal fluctuations affect vision stability, which is why pregnancy and nursing are contraindications for laser eye surgery. Candidates must wait until several months after breastfeeding has concluded. Beyond physical health, a candidate must possess realistic expectations about the potential outcomes and limitations of the procedure. While vision correction is highly successful, it does not guarantee perfect vision, and age-related changes, like the eventual need for reading glasses due to presbyopia, will still occur.
Ocular Conditions That May Disqualify Candidates
The cornea must have sufficient thickness because the procedure involves removing a small amount of tissue to reshape the eye’s surface. If the cornea is too thin, tissue removal could compromise its structural integrity, leading to a serious complication called post-LASIK ectasia, where the cornea bulges outward.
Conditions that affect the shape of the cornea, such as keratoconus, are absolute disqualifiers. This progressive disease causes the cornea to thin and bulge into a cone shape, and laser reshaping would accelerate its progression. Severe or unmanaged dry eye syndrome can also make a person ineligible, as the surgery can temporarily worsen dryness and interfere with healing. Ophthalmologists must assess tear film quality and quantity, often requiring treatment before proceeding.
Active eye infections, inflammation, or certain conditions like uncontrolled glaucoma also prevent the procedure from being performed. Glaucoma is a concern because the pressure exerted on the eye during the laser procedure can potentially exacerbate the condition. Conditions that cause corneal scarring or other structural irregularities may also interfere with the laser’s ability to create a smooth, precise correction.
Refractive Limits and Prescription Range
Laser eye surgery is most successful within specific ranges of refractive error. The amount of tissue removed from the cornea is directly related to the strength of the prescription, meaning higher corrections require more tissue removal.
If a person’s prescription falls outside these established limits, the procedure may be considered unsafe or unlikely to produce a satisfactory outcome, and alternative vision correction options are often recommended. For example, individuals with very high myopia, sometimes extending to -20.00 diopters, may be better suited for procedures like Implantable Collamer Lenses (ICLs) which do not involve corneal tissue removal. The final decision on the treatable range is highly individualized, based on the total assessment of the eye’s anatomy and health.
Typical Refractive Limits
- Myopia (nearsightedness): The treatable range typically extends up to about -10.00 to -12.00 diopters, depending on corneal thickness.
- Hyperopia (farsightedness): This generally has a narrower correction limit, often up to +4.00 to +6.00 diopters.
- Astigmatism: This can often be corrected up to a range of ±5.00 to ±6.00 diopters.
Correcting higher hyperopia prescriptions can sometimes lead to an increased risk of visual side effects, such as halos or glare, especially at night.
The Comprehensive Screening Process
A required first step for contact lens wearers is to discontinue lens use for a period, typically one to four weeks. This allows the cornea to return to its natural shape, as contact lenses can temporarily alter the corneal curvature and lead to inaccurate measurements.
The screening process involves several key diagnostic tests:
- Corneal topography and tomography: Advanced imaging creates a detailed map of the corneal surface, essential for detecting subtle irregularities and planning the precise laser treatment.
- Pachymetry: This measures the corneal thickness, providing the surgeon with the exact amount of tissue available for reshaping.
- Pupil size measurement: Measured in low light conditions, a naturally large pupil may correlate with an increased risk of night vision issues, such as glare and halos, after the procedure.
- Refraction analysis: This confirms the stability and accuracy of the patient’s prescription.
- Dilation: The eye is dilated to allow the specialist to fully examine the retina and optic nerve, ensuring there are no underlying diseases that could affect the safety or outcome of the surgery.