Understanding Refractive Errors and Laser Eye Surgery

1. Advanced Surface Ablation KHADER FARWAN

2. How the eye works • Light rays enter the eye through the clear cornea, pupil and lens. • These light rays are focused directly onto the retina, the light-sensitive tissue lining the back of the eye. • The retina converts light rays into impulses, sent through the optic nerve to your brain, where they are recognized as images. • 70% of the eye's focusing power comes from the cornea and 30% from the lens.

3. Refractive errors: myopia • The distance between the cornea and the retina may be too long or the power of the cornea and the lens may be too strong. • Four types of refractive error: • Myopia (nearsightedness) • Hyperopia (farsightedness) • Astigmatism • Presbyopia

4. Refractive errors: myopia • In myopia (nearsightedness), there is too much optical power in the eye. • The distance between the cornea and the retina may be too long or the power of the cornea and the lens may be too strong. Myopia, or nearsightedness

5. Refractive errors: hyperopia • In hyperopia (farsightedness), there is too little optical power. • The distance between the cornea and the retina may be too short. • Light rays are focused behind the retina instead of on it. • In adults (but not children), distant objects will look clear, but close objects will appear blurred. Hyperopia, or farsightedness

6. Refractive errors: astigmatism • In astigmatism, the cornea is curved unevenly—shaped more like a football than a basketball. • Light passing through the uneven cornea is focused in two or more locations. • Distant and close objects may appear blurry. Astigmatism occurs when light passes through uneven cornea

7. Refractive errors: presbyopia • Presbyopia is a normal condition in which your eyes gradually lose the ability to focus things up close. • When we are young, the lens in our eyes is flexible and is able to change focus easily between near and far objects, like an autofocus on a camera. • At around age 40, this flexibility naturally begins to gradually decrease, making it more difficult to see objects up close.

8. What is refractive surgery? • A group of outpatient surgical procedures used to alter how your eye focuses light rays on the retina, thereby improving vision and reducing dependence on glasses and contact lenses. • In most cases, refractive surgery affects the shape of your cornea to redirect how light is focused onto the retina. Popular procedures include LASIK, LASEK, PRK and CK.

9. What is refractive surgery? • Most refractive surgery is performed on the cornea and affects only the front of your eye, while the rest of your eye will change naturally as you age. • In some cases, refractive surgery procedures don’t reshape the cornea; instead, the eye’s natural lens is either replaced or enhanced by an implantable lens that helps correct vision.

10. What is Advanced Surface Ablation (ASA)? • A refractive surgery procedure where the outermost layer of the cornea, the epithelium, is removed or displaced to expose the stroma (the middle, thickest layer of tissue in the cornea). • A computer-controlled excimer laser then reshapes the front surface of the corneal stroma. The outermost layer of the cornea, the epithelium, lies on top of the stroma

11. What is Advanced Surface Ablation (ASA)? • The epithelium is either replaced or assisted in healing back over the surface of the cornea underneath a bandage contact lens. • Types of ASA: Photorefractive Keratectomy (PRK) and Laser Epithelial Keratomileusis (LASEK).

12. What is Photorefractive Keratectomy (PRK)? • Outpatient refractive surgery used to treat nearsightedness (myopia), farsightedness (hyperopia) and astigmatism. • PRK involves: • Manually removing the corneal epithelium. • Using an excimer laser to precisely sculpt the stroma according to the specific refractive error to be treated. • Covering the cornea with a bandage contact lens to facilitate healing of the epithelium. • The goal of PRK is to focus light rays more precisely on the retina to improve uncorrected vision.

13. What is PRK? • To treat myopia, the surgeon uses the laser to flatten the corneal surface in a lenticular (lens-like) pattern. • By reducing the curvature of the cornea, the eye’s focusing power is decreased. • Images that are focused in front of the retina are pushed closer to or directly onto the retina, producing clearer uncorrected vision. With myopia, the laser is used to flatten the corneal surface

14. What is PRK? • To treat hyperopia, the surgeon uses the laser to steepen the cornea by removing tissue from the periphery of the cornea. • By steepening the cornea, the focusing ability of the cornea is changed, thereby adding refractive power to focus the incoming images more directly on the retina instead of behind it.

15. What is PRK? • To treat astigmatism, the laser is programmed to selectively reshape specific portions of the cornea more than others. • The laser flattens areas that are steeper than normal and steepens areas that are flatter than normal, usually in an elliptical pattern. • Allows the surgeon to deliver the correct amount of laser energy to the appropriate areas of the cornea, thereby improving uncorrected vision.

16. How is PRK performed? • In addition to a complete pre-operative eye exam, measurements are taken to give the surgeon the necessary information to perform the procedure: • Refractive error measurement. • Pupil evaluation and measurement. • Tonometry: measurement of your eye’s intraocular pressure (fluid pressure inside your eye). • Corneal topography: mapping the surface details of the cornea. • Keratometry: measurement of the form and curvature of the cornea. • Pachymetry: measurement of corneal thickness. A phoropter is used to measure refractive errors

17. How is PRK performed? • Anesthetic eyedrops are applied to your eye(s). • The non-treated eye is patched.

18. How is PRK performed? • A lid speculum is placed to keep the eyelids open during the procedure.

19. How is PRK performed? • The epithelium is removed using an Amoils brush or by using the laser itself. An Amoils brush is used to remove the epithelium

20. How is PRK performed? • An excimer laser controlled by a computer is programmed to reshape the cornea, depending on the amount and type of correction desired. • The laser sculpts an area six to nine millimeters in diameter on the surface of the eye, depending on whether the laser is correcting for myopia or hyperopia. • The depth of the sculpting depends on the degree of correction needed.

21. How is PRK performed? • The laser removes tissue from the cornea, either decreasing the steepness of curvature for nearsightedness or increasing the steepness of curvature for farsightedness. With myopia, the laser is used in a central, circular pattern

22. How is PRK performed? • After the procedure, a transparent bandage contact lens is placed over the cornea to promote healing… …and postoperative eyedrops are applied.

23. Considerations for PRK surgery • May be recommended for people with lower levels of myopia or hyperopia, although it is FDA approved to treat between -12 to +6 diopters of refractive error. • May be recommended for people with thin corneas who would not be good candidates for LASIK. • May be recommended for people with dry eyes. • Because a stromal flap is not created in the cornea (as with LASIK), less corneal tissue is disturbed, therefore some surgeons consider PRK to be a safer procedure than LASIK. • Certain occupational restrictions against other forms of refractive surgery (i.e., LASIK). • Less invasive procedure than intraocular surgery, thus reducing quality-of-vision complaints.

24. Considerations against PRK surgery • Slower visual recovery than LASIK or phakic IOL surgery. • Not recommended for people with significant ocular disease of any type, especially corneal disease. • Not recommended for people with significant skin or systemic disease that could adversely affect healing. • Not recommended for people with a history of excessive scarring when skin is broken. • Not recommended for people with unstable or changing refractive error. • Some discomfort immediately following surgery, lasting for 2 to 3 days, occasionally requiring narcotics or topical anesthetics for pain control.

25. Risks and possible side effects of PRK surgery • Over-correction or under-correction (with a possible need for a re-treatment). • Vision may be blurry for a few days up to several weeks, with the achievement of best vision taking up to a month or longer. • Glare and halos around lights, particularly at night. • Corneal scarring and corneal haze. • Corneal infection.

26. What is Laser Epithelial Keratomileusis (LASEK)? • Outpatient refractive surgery useful in correcting nearsightedness (myopia), farsightedness (hyperopia) and astigmatism. • LASEK involves: • Temporarily displacing the corneal epithelium using dilute alcohol. • Using an excimer laser to precisely sculpt the stroma according to the specific refractive error to be treated. • Replacing the epithelium and using a bandage contact lens to speed healing and reduce discomfort. • The goal of LASEK is to focus light rays more precisely on the retina to improve uncorrected vision.

27. How is LASEK performed? • As with other procedures, pre-operative measurements are taken of your eye. • A special alcohol solution is used to loosen the epithelium… …which allows it to be peeled back from the cornea.

28. How is LASEK performed? • Once the epithelium is displaced, an excimer laser controlled by a computer is programmed to reshape your cornea.

29. How is LASEK performed? The laser removes tissue, either decreasing the curve of your cornea to correct nearsightedness or increasing the curve of your cornea to correct farsightedness. After the laser treatment, the epithelium is smoothed back into position over the cornea, and a bandage contact lens is placed to promote healing.

30. How is LASEK performed? • The reshaped cornea focuses light more accurately on the retina.

31. Considerations for LASEK surgery • May be recommended for people with lower levels of myopia or hyperopia. • May be recommended for people with thin corneas who would not be good candidates for LASIK. • May be recommended for people with dry eyes. • Because a stromal flap is not created in the cornea (as with LASIK), less corneal tissue is disturbed, therefore some surgeons consider LASEK to be a safer procedure than LASIK. • Certain occupational restrictions against other forms of refractive surgery (i.e., LASIK). • May be less painful during healing than PRK. • May offer faster visual recovery than PRK (but not as fast as LASIK). • Less invasive procedure than intraocular surgery, thus reducing quality-of-vision complaints.

32. Considerations against LASEK surgery • Slower visual recovery than LASIK or phakic IOL surgery. • Not recommended for people with significant ocular disease of any type, especially corneal disease. • Not recommended for people with significant skin or systemic disease that could adversely affect healing. • Not recommended for people with a history of excessive scarring when skin is broken. • Not recommended for people with unstable or changing refractive error. • Not recommended for people with myopia, hyperopia or astigmatism beyond the range of PRK. • Some discomfort immediately following surgery, lasting for 2 to 3 days, sometimes requiring narcotics or topical anesthetics for pain control.

33. Risks and possible side effects of LASEK surgery • Over-correction or under-correction (with a possible need for a re-treatment). • Vision may be blurry for a few days up to several weeks, with the achievement of best vision taking up to a month or longer. • Glare and halos around lights, particularly at night. • Corneal scarring and corneal haze. • Corneal infection.

34. Is refractive surgery right for you? • New surgical procedures, including PRK and LASEK, are creating more opportunities for people who want to be less dependent on glasses or contacts. • Surgery may not entirely eliminate your need for corrective lenses. Glasses/contacts may still be needed for activities such as fine or detailed work, reading and perhaps night driving.

35. Is refractive surgery right for you? • A large part of the success of any refractive surgery depends on your understanding of the procedure and your expectations. • Since refractive surgery is an elective procedure, you have the opportunity and responsibility to become fully informed about its risks and benefits. • Your ophthalmologist will explain the specific technique, its benefits, as well as possible risks and side effects associated with your case.

36. Discuss options and questions with your ophthalmologist • With the help of your ophthalmologist, it’s ultimately your responsibility to weigh the risks and side effects of a procedure with the benefits it has to offer. • If you decide refractive surgery is right for you, you may join millions of people who have reduced their dependence on glasses or contacts.