LASIK is a well-known procedure for reshaping the eye’s surface to correct vision, and while it is most commonly associated with fixing nearsightedness, it can also be used for farsightedness, or hyperopia. The application of LASIK for hyperopia is a distinctly different approach than the one used for other refractive errors. The procedure requires a specialized method to achieve the desired visual outcome. Patient suitability is determined by specific criteria, including the degree of the prescription and other characteristics of the eye. This surgical option offers a path to reduced reliance on corrective lenses for many individuals with hyperopia.
How Farsightedness Affects Vision
Farsightedness, medically termed hyperopia, is a common refractive error where light entering the eye focuses at a point behind the retina instead of directly on its surface. This misfocus happens because the eyeball is typically shorter than average along its front-to-back axis. Alternatively, the cornea, the clear front surface of the eye, may have a flatter curvature than necessary. Both a short axial length and a flat cornea result in insufficient focusing power for the eye’s length.
The consequence is that distant objects can often be seen clearly, but objects up close are blurry or difficult to focus on. For a hyperopic eye to achieve clear vision, the eye must constantly exert effort to increase its focusing power, a process called accommodation. This continuous accommodative effort can lead to symptoms like eye strain, headaches, and fatigue, particularly after prolonged reading or close-up work.
The Mechanism of LASIK for Hyperopia
LASIK corrects hyperopia by changing the shape of the cornea to increase its refractive power, ensuring light focuses correctly on the retina. The procedure begins with the creation of a thin, hinged flap on the cornea’s outer layer, which is then gently lifted to expose the underlying stroma. An excimer laser is then used to remove microscopic amounts of tissue with precision.
The mechanism for hyperopia correction is opposite to that of myopia correction, which aims to flatten the central cornea. To correct hyperopia, the central cornea must be made steeper to increase the total focusing power of the eye. The excimer laser achieves this by ablating tissue in a ring-shaped pattern around the outer edges of the cornea’s center. By removing more tissue peripherally, the center of the cornea is effectively pulled forward, steepening its curvature.
Once the laser ablation is complete, the corneal flap is carefully repositioned over the treated area, where it adheres without stitches. This steepening causes light rays to bend more sharply, shifting the focal point forward onto the retina. The stability and predictability of hyperopic correction can be more challenging than myopic correction due to the nature of the corneal reshaping required.
Suitability and Prescription Limits
Determining suitability for hyperopic LASIK involves a comprehensive eye examination and consideration of specific patient and prescription factors. Hyperopic LASIK is generally limited to lower prescriptions because the required steepening of the cornea can be less stable than the flattening used for nearsightedness. The maximum prescription that can be safely treated typically ranges from +4.00 to +6.00 Diopters (D), though many clinics prefer to treat up to about +4.00 D to maximize predictability. A stable prescription with no significant changes for at least 12 months is generally required to ensure long-term stability of the surgical result.
Corneal Integrity
Corneal thickness is an important factor, as the procedure requires sufficient residual tissue to maintain the eye’s structural integrity after ablation. Surgeons must ensure a minimum thickness remains in the corneal stroma to prevent complications like corneal ectasia, a progressive weakening of the cornea. Corneal thickness measurement, known as pachymetry, is performed during the initial consultation.
Age and Presbyopia
Patient age plays a significant role in determining candidacy because the eye’s ability to accommodate naturally declines with age, a condition known as presbyopia. For patients over 40, hyperopia correction may be complicated by presbyopia. Alternative procedures like Refractive Lens Exchange (RLE) may be considered to address both distance and near vision issues simultaneously.