History of vision surgeries
Utilizing a surgical procedure to alter structures within and around the eye to help optimize vision dates back to between 1792 and 1750 BCE. The first type of refractive surgery, which was mentioned in the Code of Hammurabi, was a procedure called “couching” that use a sharp object to poke the cloudy crystalline lens to the back of the eye.
Fast forward to modern times where solutions to refractive error primarily take place on the cornea. Below is a summary of some of these modern refractive procedures that can be performed on the cornea to make the ametropic eye into the emmetropic eye.
While the list below is a comprehensive list of all corneal refractive procedures, some have come and gone out of favor with refractive surgeons due to risk and reliability of visual outcome. It is important to note that final visual outcome cannot be guaranteed and risks, while rare, for all procedures include, but are not limited to, infection, inflammation and possible loss of vision and/or blindness. It is important that all risks including presbyopia are discussed with all patients by all doctors that interact or co-manage the refractive patient. Pre-treatment considerations of calculated post-treatment corneal pachymetry, residual keratometric measurements must be performed for all procedures.
Non-Laser Based Refractive Procedures
Radial Keratectomy (RK)
- Indication: Myopia and Hyperopia correction
- Procedure: Radial incisions are made in the peripheral stroma with a diamond knife. This causes normal intraocular pressure to push the peripheral cornea outward while the central corneal flattens, ultimately reducing myopia. (1)
- Risks: Unstable refractive error (mild to severe), overcorrection, neovascularization of incision, irregular incision, penetration into anterior chamber, structural weakening of cornea, increased risk of perforation from trauma
- Special considerations: Due to the variability in final refractive error outcome and weakened structural integrity of the cornea, this procedure is rarely performed anymore. RK should not be performed on individuals with corneal ectasia, corneal disease and those in a position to have an increased likelihood of eye trauma such as Service members, police officers, athletes that compete in contact sports, etc.
Intrastromal Corneal Rings (Intacs)
- Indication: Correction of low amounts of spherical myopia and improvement of vision for the keratoconic cornea (2)
- Treatment range: -0.75D to -3D
- Procedure: Polymethylmethacrylate (PMMA) rings are inserted into the peripheral stroma to elevate the peripheral cornea and flatten the central cornea. Intrastromal corneal rings can also manipulate and regularize a cone in the keratoconic cornea.
- Note: This procedure does NOT cure keratoconus. The only procedure that is FDA approved to halt or slow the progression of Keratoconus or other ectactic disease is Corneal Cross Linking (CXL).
Conductive Keratoplasty (CK)
- Purpose: Presbyopia and low hyperopia correction
- Treatment range: +0.75D to +3.00D with less than -.75D of astigmatism
- Procedure: Heat from radio waves are used to shrink the collagen fibers in the peripheral corneal stroma, causing the central cornea to steepen.
- This procedure has fallen out of favor as a refractive procedure for presbyopia. It is currently being used in conjunction with CXL to manipulate the shape and location of the cone in an eye with Keratoconus.
Laser Based Procedures
Photorefractive Keratectomy (PRK)
- Purpose: Myopia, Hyperopia, and Astigmatism correction
- Approximate Treatment range: -8D to +4D, up to 4D of cylinder.
- Procedure: The corneal epithelium is removed to exposed Bowman’s Layer. The excimer laser is applied to Bowman’s layer ablating through the tissue where is removes the corneal stroma. This is done centrally for myopic individuals and peripherally in hyperopic individuals. Post-laser ablation, a bandage contact lens is places on the cornea to facilitate epithelial recovery and healing.
- Risks: Post-treatment pain, slow epithelial recovery, slow visual recovery, corneal infiltrate and/or infection, post-treatment corneal haze formation.
- As a general (but not absolute) rule, 400um of residual corneal must remain after the PRK procedure.
Laser-assisted in situ keratomileusis (LASIK)
- Purpose:Myopia, Hyperopia, and Astigmatism correction
- Approximate Treatment range: -10D to +4D, up to 4D of cylinder
- Procedure: a thin flap is created in the stromal cornea using a microkeratome blade or a femtosecond laser. The flap is then retracted back and the excimer laser is applied to ablate the anterior stromal bed. After completion of the excimer ablation, the cornea if hydrated and the flap is reflected back into its normal anatomical position.
- Side effects: pain, infection, flap complications (button holes, free caps, flap folds, etc).
- Special considerations:
- A minimum of 250 microns of corneal tissue must remain posterior to the flap after all surgery is completed. If an enhancement after the initial procedure is indicated, more than 250 microns of corneal tissue is required to account for additional tissue removal.
- In comparison to patients who undergo PRK, individuals who undergo LASIK generally experience faster healing time, shorter duration of pain, and less post-treatment corneal haze.
- Indication: Myopia, Hyperopia and Astigmatism correction
- Approximate treatment range: same as LASIK
- A hybrid of PRK and LASIK. A blunt plastic blade is used to create an epithelial flap only. Once the epithelial flap is reflected, the excimer laser is applied to the corneal stroma. The flap is then reflected and placed back into its normal anatomical position. A bandage contact lens is placed on the cornea to facilitate epithelial remottling. This procedure would technically leave more residual corneal tissue, however, like RK, has fallen out of favor of corneal surgeons due to its increased healing time and associated discomfort.
- Types of Eye Surgery for Refractive Errors. Johns Hopkins Medicine. https://www.hopkinsmedicine.org/healthlibrary/conditions/eye_care/corrective_eye_ surgery_for_refractive_errors_85,P00515.
- Cheatham, K, Cheatham, M, Wood, K. KMK Part 1 Applied Science Review. 10th ed. Omaha, NE: KMK Educational Services LLC; 2017.
- This image was originally published in the Retina Image Bank. Jason S. Calhoun. Radial Keratotonomy (RK). Retina Image Bank. 2013; Image Number 7731. © the American Society of Retina Specialists.
- This image was originally published in the Retina Image Bank. Nichole Lewis. Corneal implant INTACS. Retina Image Bank. 2017; Image Number 27655. © the American Society of Retina Specialists.