What is Refractive Surgery?
When light rays enter the eye, they need to be brought together to form an image or come into focus. The eye does this by bending and focusing the light as it passes through the cornea (clear front part of the eye) and the lens inside the eye. The goal is to get the image to focus clearly on the retina. Think of the eye like a camera and the retina is the film of the camera. Having a clearly focused image on the retina will give you your best vision. In patients who are nearsighted or farsighted, images do not come into focus on the retina because the cornea and lens have too much or too little power for the length of the eye. This is called a refractive error. Glasses and contact lenses either increase or decrease the power of the eye to help bring images into focus on the retina again.
The goal of refractive surgery is to improve the vision by correcting refractive errors. In patients who are nearsighted, the eye has too much power and in patients who are farsighted, the eye has too little power for the length of the eye. By doing surgery on the cornea or inside the eye, we can adjust the power of the eye to bring images into better focus. LASIK and PRK are examples of surgery on the cornea that use lasers to ablate (remove) tissue and change the shape of the cornea. Implantable Collamer Lens (ICL) and Refractive lens exchange (RLE) are inside the eye surgeries that change the power of the eye without altering the cornea shape. Each type of surgery has advantages and disadvantages and it is important to understand the options so you can make the best choice for you.
Overview of Refractive Options
Options for improving the vision in myopia (nearsightedness) include glasses, contact lenses, refractive lens exchange (RLE), PRK and LASIK, and Implantable Collamer Lens (ICL) surgeries. Options for hyperopia (farsightedness) include glasses, contact lenses, refractive lens exchange, and LASIK and PRK. Each option has its advantages and disadvantages.
Glasses are the lowest risk however they offer a lower quality of the vision due to minification or magnification of images and the limitation of peripheral vision caused by high power lenses. Contact lenses provide high-quality vision but include risks such as eye infections, dry eye, limbal stem cell failure, allergy, and irritation.
Lens Based vs Cornea Based Refractive Surgery
Refractive cornea surgery options such as LASIK (Laser-assisted in situ keratomileusis) and PRK (Photorefractive Keratectomy) ablate or remove corneal tissue to reshape it and improve the vision. These laser procedures are designed to increase or decrease the power of the cornea to correct the refractive error. The quality of the vision after LASIK and PRK is excellent however some patients may notice glare and halos (especially at night) and worsening of dry eye. For the majority of patients these vision and dry eye changes last a few months and then resolve. There are limitations to the amount of cornea ablation (the amount of treatment) that can be safely done, which disqualifies some highly nearsighted and highly farsighted patients for LASIK and PRK.
Refractive lens-based surgery options such as RLE (refractive lens exchange) and ICL (Implantable Collamer Lens) do not remove corneal tissue. These options correct the refractive error by inserting a lens in the eye. The RLE option removes the lens inside your eye and replaces it with a lens implant similar to cataract surgery. This can provide excellent vision but for patients who are highly myopic (nearsighted) it can be associated with increased risk of retinal tear or detachment after surgery. The ICL option does not remove the lens in your eye but adds a lens implant in front of it. ICL surgery provides excellent, high quality vision but has an increased risk of glaucoma (high eye pressure), cataract formation, and corneal edema. ICL surgery is only for high myopia (nearsighted) patients.
LASIK Refractive Surgery
LASIK (Laser-assisted in situ Keratomileusis) is a very effective procedure to reduce or eliminate myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. It is primarily intended to give someone excellent distance vision without the need for glasses or contact lenses. The procedure involves creating a flap using a laser or microkeratome, lifting the flap back and reshaping the cornea with a different laser to change its power, and then putting the flap back down. The procedure takes a few minutes to complete and generally is painless (though feeling cold water and pressure is common).
The benefits of LASIK, aside from being a quick procedure, are that it is a reliable procedure that generally has excellent outcomes and the vision recovery is rapid (usually a few days). Please note that it is common to see halos especially at night which can take a few months to fully resolve. It is also common for patients to experience worsening of dry eye which can last for months but also typically resolves. LASIK surgery is not recommended if you are pregnant or breast feeding.
While LASIK is excellent at restoring good uncorrected distance vision, if you are over the age of 40 or already need reading glasses or bifocals to see up close, you will probably continue to need glasses for reading after LASIK. If using reading glasses after LASIK is not your goal, you may want to consider monovision in which one eye is corrected for distance vision, while the other eye is corrected for reading vision. Monovision may take some time to adjust to if you have not worn monovision contact lenses in the past. If you are considering monovision, a contact lens or glasses trial is recommended beforehand.
The risks of LASIK include: over-correction or under-correction, flap dislocation, dry eye, glare and halos, continued need for glasses or contact lenses to see clearly, irregular astigmatism, corneal ectasia (warping/unstable cornea), corneal haze or scarring, infection, problems creating the LASIK flap, epithelial ingrowth beneath the LASIK flap, inflammation under the flap, night vision complaints, and difficulty selecting the correct lens implant power if you have cataract surgery in the future. LASIK requires placement of a suction ring on the eye to create the flap and the pressure used in this step may cause optic nerve damage in patients with pre-existing optic nerve disease like glaucoma. The dry eye changes seen after LASIK are temporary for many patients (typically 4-6 months) though in some the dry eye changes may be longer lasting or permanent.
PRK Refractive Surgery
PRK (PhotoRefractive Keratectomy) is a very effective procedure to reduce or eliminate myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. It is primarily intended to give someone excellent distance vision without the need for glasses or contact lenses. The procedure involves removing the surface epithelium (skin) from the cornea and reshaping the cornea with a laser to change its power. The eye is covered with a bandage contact lens while the epithelium heals (typically over the course of 1-2 weeks. The procedure takes a few minutes to complete and generally is painless (though feeling cold water and pressure is common). PRK surgery is not recommended if you are pregnant or breastfeeding.
The benefits of PRK, aside from being a quick procedure, are that it is a reliable procedure that generally has excellent outcomes and the vision recovery is quick (may take a few weeks to fully stabilize). The vision recovery is not as rapid in PRK as in LASIK because as the epithelium covers back over the cornea it will take a few weeks to fully complete remodeling. The vision will fluctuate during this time of epithelium remodeling and that is normal. Another benefit of PRK is there is no flap as there is in LASIK, so no risk of flap dislocation. Please note that it is common to see halos especially at night which can take a few months to fully resolve. While PRK is excellent at restoring good uncorrected distance vision, if you are over the age of 40 or already need reading glasses or bifocals to see up close, you will probably continue to need glasses for reading after PRK. If using reading glasses after PRK is not your goal, you may want to consider monovision in which one eye is corrected for distance vision, while the other eye is corrected for reading vision. Monovision may take some time to adjust to if you have not worn monovision contact lenses in the past. If you are considering monovision, a contact lens or glasses trial is recommended beforehand.
During PRK, Bowman’s protective membrane is removed from the front of the eye and it does not grow back. This Bowman’s membrane protects against the sun’s harmful UV rays. If you have PRK surgery, you must wear UV blocking sunglasses at all times when outside (even on cloudy days) to reduce your risk of corneal haze or scarring.
The risks of PRK surgery include over-correction or under-correction of your vision, dry eye, glare and halos, the continued need for glasses or contact lenses to see clearly, irregular astigmatism, corneal ectasia (warping/unstable cornea), corneal haze or scarring, infection, night vision complaints, and difficulty selecting the correct lens implant power if you have cataract surgery in the future. Dry eye changes seen after PRK are temporary for many patients (typically 4-6 months) though in some the dry eye changes may be long-lasting or permanent.
ICL Refractive Surgery
ICLs, or Implantable Collamer Lenses, are used to correct blurry vision caused by moderate to high myopia. ICL surgery is especially useful for patients who have high myopia as many are not candidates for LASIK or PRK surgery. During ICL surgery, a thin lens (similar to a contact lens) is inserted into the eye behind the iris and in front of your native lens. No tissue is removed, making the procedure potentially reversible. ICL surgery requires that you have a stable glasses or contact lens prescription for at least 1 year which means that your prescription does not change by more than 0.5 diopters. ICL surgery is not recommended if you are pregnant or breastfeeding.
If you wear contact lenses you will need to stay out of your lenses prior to pre-operative testing and measurements. If you wear soft contact lenses, stop wearing them 1 week prior to testing. If you wear toric lenses, stop wearing them 2 weeks prior to testing. If you wear rigid or hard contact lenses like a gas permeable, a scleral, or a hybrid lens please stop wearing the 1 month before your testing visit.
Since ICL surgery does not change the shape of the cornea, it provides a very high-quality vision. It also maintains the ability to see things up close because the natural lens is preserved. There is less risk of night vision complaints, glare and halos, and contrast sensitivity decreased after surgery compared to LASIK and PRK.
The main risks include over-correction or under-correction of your vision, elevated eye pressure and angle-closure glaucoma. This risk is reduced by making openings in the iris with a laser before surgery called peripheral laser iridotomies. The iridotomies allow the fluid produced inside the eye to continue to reach the drain of the eye after surgery. There is a risk of cataract formation after the surgery which could affect your vision. Should you develop a cataract, the ICL may need to be removed and you may need cataract surgery. There is also a risk of damage or loss of the endothelial pump cells which live on the inside of the cornea. These endothelial cells are necessary to keep the cornea clear and damage or loss of these cells can lead to corneal clouding, corneal edema, and in severe cases lead to needing a cornea transplant. ICL surgery is intraocular surgery, so it carries the same risks of other intraocular surgeries.
Refractive Lens Exchange Surgery
A refractive lens exchange (RLE) or clear lens exchange (CLE) surgery, involves the removal of the clear lens of your eye, even though there is no cataract or only a mild one. Your eye surgeon will surgically remove the natural lens of the eye and replace it with an intraocular lens implant (IOL) in order to restore your vision. This is an artificial lens, usually made of silicone or acrylic material, which is permanently placed inside the eye.
In patients who are farsighted or nearsighted, the power of the lens in your eye is mismatched for the length of your eye. This causes images to be blurry. Replacing the lens in your eye with a lens of a more appropriate power can help you see better by focusing the images clearer on your retina. Although this can improve your natural distance vision, you will lose the natural up-close focusing power of the eye (called accommodation). As a result, you will need to have near vision restored with reading glasses, Monovision, or a Multifocal/Advanced technology lens implant.
For Monovision RLE, your eye surgeon will implant one eye with a lens power for distance vision and the other eye with a lens power for near vision. This combination of a distance eye and a reading eye enables you to read without glasses. Monovision can reduce depth perception and take a long time to adjust to, therefore it is typically recommended that this option be tried with contact lenses prior to having monovision surgery. For the multifocal (advanced technology) lens implant, the implant tries to provide a range of vision (distance, intermediate, and/or near) by splitting light as it enters the eye.
Measurements for RLE surgery are called biometry and they are very important for determining the lens implant power needed to improve the vision. If you wear soft contact lenses, you need to leave them out of the eyes for 1 week before having measurements for surgery. Rigid (gas permeable, hybrid, or scleral) lens wearers should leave lenses out for four weeks. While biometry is very accurate for most patients, the final vision result may be different from what was planned. As the eye heals, the lens can shift very slightly in position and the amount of this shift is not the same in everyone. Patients who are highly nearsighted or highly farsighted have the greatest risk of differences between planned and actual vision outcomes. Patients who have had LASIK or other refractive surgeries are especially difficult to measure precisely. If the eye’s visual power after surgery is considerably different than what was planned, surgical replacement of the IOL might be considered.
The Risks of RLE surgery include increased glare and/or halos, ghosting of images, difficulty driving at night and reduced contrast sensitivity. Multifocal lenses can reduce dependence on glasses but are associated with an increased likelihood of these vision complaints. If you drive a considerable amount at night, or perform detailed “up-close” work more than just reading, a monofocal lens with glasses for up-close work may be a better choice for you. If a monofocal lens is selected without choosing monovision, then either reading or distance glasses/contact lenses will be needed. For Monovision patients, you may have problems with impaired depth perception or balance and it can take several months to fully adapt to your new vision. Monovision patients may still prefer to wear glasses for some activities such as reading or distance activities such as driving (especially at night).
Regardless of your pre-operative lens selection, your surgeon may need to implant a different lens or no lens at the time of surgery depending on the strength of the support structures in your eye. While the selection of the proper IOL based upon sophisticated equipment and computer formulas is not an exact science. After your eye heals, its visual power may be different from what was predicted by preoperative testing. You may need to wear glasses or contact lenses after surgery to obtain your best vision. Additional surgeries such as IOL exchange, placement of an additional IOL, or refractive laser surgery could be considered if you are not satisfied with your vision after RLE.
The risks of refractive lens exchange surgery are essentially the same as cataract surgery which includes but are not limited to bleeding, infection, rupture of the capsule that supports the lens, corneal swelling (edema), retinal swelling (cystoid macular edema), and retinal tear or detachment. RLE surgery is not recommended if you are pregnant or breastfeeding.