Photorefractive keratectomy is a surgical procedure that removes an outermost portion of the cornea and then uses laser to change the shape of the cornea in order to correct vision problems, such as nearsightedness, farsightedness and astigmatism. With topography-guided photorefractive keratectomy (TG-PRK), corneal topography is used to create three-dimensional maps of the cornea’s surface prior to the laser treatment. This information is combined with the patient’s refractive error to develop a precise and personalized vision correction plan using the laser technology.
Corneal topography is a computer assisted diagnostic tool that creates a three-dimensional map of the surface curvature of the cornea. The cornea is the transparent, outermost layer of the eye and it plays an important role in focusing your vision. An evenly rounded cornea results in normal vision. If a cornea is irregularly shaped, such as too steep, flat or unevenly curved, vision will be impaired. Corneal topography produces a detailed, visual map of the cornea’s shape and power. This detailed information is used to diagnose, monitor, and treat various eye conditions. It is also used in fitting contact lenses and for planning surgery, including laser vision correction. For laser vision correction the corneal topography map is used in conjunction with other tests to determine exactly how much corneal tissue will be removed and which ablation pattern will be used.
As done with PRK, the procedure begins by gently removing the central portion of the corneal coating, or epithelium, using a special solution or a surgical device. Once the epithelium is removed, a laser that is programmed with the patient’s topographic and refractive measurements is used to gently remove microscopic amounts of the corneal tissue so it can be reshaped. A special contact lens will be placed on the to protect the cornea while new epithelial cells form, a process that takes several days.
Keratoconus is a chronic disease in which the cornea, the clear dome-shaped surface of the eye, thins out and bulges like a cone. This in turn causes light rays to become out of focus, resulting in blurry and distorted vision. Additionally, the irregular shaped cornea makes it difficult for keratoconus patients to wear contact lenses or have improved vision with glasses.
In TG-PRK for keratoconus, the laser is used to correct the cone-shaped corneal irregularities which cause decreased visual function. By using the patient’s custom corneal topography data, the laser reshapes the corneal surface to improve the cornea’s shape and visual performance. The goal is to improve the cornea’s architecture in order to enhance vision with glasses or contact lens fit, depending on the need of the patient.
TG-PRK is performed on keratoconus patients who have undergone, corneal collagen crosslinking (CXL), a procedure that uses riboflavin and ultraviolet light to strengthen the cornea fibers of the eye. When used in combination with CXL, TG-PRK is shown to improve the visual performance of keratoconus patients.
TG-PRK may also be used to treat LASIK complications, corneal scarring and other irregularities of the cornea including.