Journal of Refractive Surgery

Editorials Free

Quality of Vision and Freedom from Optical Correction after Refractive Surgery

George O Waring, III, MD, FACS, FRCOphth

Nearly half of the population of North Amercia has myopia; the prevalence of myopia in other populations ranges from 2 to 60%, as McCarty and colleagues document in this issue of the Journal (pp. 229-234). The ideal goal of refractive surgery for such individuals is to eliminate the need for distance optical correction and to allow them to see as well as- or better than- they could with spectacles or contact lenses. In 1997, we have only partially achieved that goal.

In this issue of the Journal (pp 300-301), Werblin1 opines that the goal of refractive surgery is 20/20 or better uncorrected visual acuity and "patients will not be happy until refractive surgery is able to satisfy this need." After contemporary refractive keratotomy, photorefractive keratectomy (PRK), excimer laser in situ keratomileusis (LASIK), intrastromal corneal ring segment insertion, and phakic intraocular lens (IOL) implantation, approximately 50 to 60% of patients with myopia of -10.00 diopters (D) or less, see 20/20 or better uncorrected at approximately 1 year after surgery, but well over 90% could see 20/20 or better before surgery- with optical correction. At the 20/40 level, commonly referred to as driver's license vision, we are doing much betterover 90% of operated eyes achieve this level.

A significant proportion of patients wear an optical correction after refractive surgery- either part-time (eg, night driving) or full-time. For example, in the PERK study at 6 years after surgery, 36% (167) of patients younger than 40 years of age wore lenses for distance or near vision.2 Unfortunately, published data on how many patients wear spectacles and contact lenses after refractive surgery is almost nonexistent-a remarkable indictment of clinical reporting from the refractive surgical community, since the most important criterion of success for patients who have refractive surgery is freedom from corrective lenses.

It is not only the refractive outcome after surgery that determines spectacle wearing status, but also the stability of refraction over time. Changes in refraction may occur from the surgical procedure itself. A hyperopic shift after radial keratotomy has been well documented3; shorter corneal incisions may decrease the hyperopic shift4 but long-term follow-up data at 3 to 10 years have not been published. Sawelson and colleagues5 attributed the hyperopic shift to physiological changes in the refractive state of the eye rather than to continued flattening of the cornea, a contention refuted by the data of Ellingsen and colleagues6 in this issue of the Journal (pp 223-228). After photorefractive keratectomy, a loss of initial effect (myopic regression) occurs commonly but is highly variable with different excimer lasers and surgical techniques. Emerging data on LASIK demonstrate considerable stability of refractive outcome. Synthetic procedures such as the intrastromal corneal arc segments and phakic IOLs produce quite stable refractions over many years.7,8

The changes in refraction over time may occur from normal physiological aging, as presented by Ellingsen and colleagues.6 Current concepts usually state that simple myopia is stable by the late teens or early 20s, and this is commonly the earliest age at which refractive surgery is recommended. These findings are based on studies carried out 30 to 50 years ago.9"12 Ellingsen and colleagues6 point out that simple myopia increases on the average by - 0.60 D in a patient's 20s, -0.40 D in a patient's 30s, and -0.30 D in a patient's 40s, but then switches to a hyperopic shift with increases of +0.30 D in the patient's 50s, and +0.40 D in the 60s. This lends importance to informing patients- before surgery-that their eyes may change with age and that they may have to wear spectacles some of the time for best distance vision in the future. Even a perfect piano result shortly after refractive surgery is likely to undergo refractive shifts with time- including the shift toward presbyopia in a patient's 40s.

Refractive surgeons and their staffs should create realistic expectations for patients by not promising "freedom from glasses" but rather emphasizing a decreased dependence on glasses. I personally never promise a patient that I can completely eliminate the need for distance glasses or contact lenses with refractive surgery and always emphasize the possible need for part-time use of spectacles: "Our goal is to get you out of glasses and contact lenses as much as possible, but you may have to wear spectacles about 10% of the time- for example, for driving at night." This communication is important, not only in the surgeon's consulting room, but also in public communications, news articles, and advertisements. If refractive surgeons hold out the promise of total freedom from optical correction, ignoring the occasional need for glasses (and the need for reading glasses in presbyopes), our trustworthiness will be called into question by the public, the news media and our colleagues; our patients will be disappointed-feeling both a sense of failure about the surgery and a sense of betrayal about their surgeon. Refractive surgery will develop a bad reputation, with the opposite effect wished by those proffering over-zealous advertising- a decrease in refractive surgery business.

Observations about the quality of a patient's vision after refractive corneal surgery are difficult to make, because we have no reliable way to measure quality of vision clinically, in spite of our attempts to use contrast sensitivity and glare tests. It is a well published fact that over 90% of patients who have refractive corneal surgery would elect to have it again, would recommend it to a friend, and express overall satisfaction with the results. But, such positive conclusions are often punctuated by a patient adding, "But, I wish I saw as sharply as I did with my glasses... 1 wish I didn't see halos and lines and ghost images." A recent patient of mine had bilateral simultaneous LASIK to correct a refractive error in right eye: -4.50 +0.75 x 90° and left eye: -4.00 D sphere. At 6 months the outcome in his right eye was -0.25 +0.50 ? 90° with 20/16 uncorrected visual acuity, and in the left eye, piano with 20/12 uncorrected visual acuity. He was very satisfied with his "miraculous sight" but complained persistently of a slight "blurriness and smudginess" in his vision. I spent a long time discussing why he did not see as sharply as he did with his contact lenses before surgery.

It is not difficult to understand such a decline in the quality of vision because every time we do refractive corneal surgery, we create an abnormally shaped cornea, converting the normal prolate shape that is steeper in the center and flatter in the periphery, to an oblate shape that is flatter in the center with an inflexion zone of change in refractive power paracentrally. Even the intrastromal corneal ring segments, which retain a prolate shape, change the physiologic contours of the cornea. These new corneal shapes, with their varying refractive power, coupled with whatever opacities result from the corneal surgery, create optical aberrations and intraocular fight scattering that increase as the pupil dilates, as clearly described by Applegate and Howland in this issue (pp 295-299)13 and by Oliver and colleagues (pp 246-254). 14

Refractive surgeons have continuously devised new methods to reduce these optical aberrations: 1) larger diameter central clear zones and a reduced number of incisions in refractive keratotomy, 2) larger diameter ablation zones with more gradual edge taper in photorefractive keratectomy and LASIK, and 3) larger diameter corneal flaps without sutures and more refined methods of handling flaps in keratomileusis. Further refinements are needed to eliminate optical aberrations.

Phakic intraocular lenses hold the promise of decreasing optical aberrations because the corneal contours remain normal. An IOL has the potential of minimizing optical aberrations and intraocular light scattering if it has a large diameter optic (ideally 7 mm), if it remains properly centered on the pupil (to keep the edge behind the iris), if it is manufactured to exquisite optical tolerance, and if it is foldable to reduce the size of the surgical wound and the amount of induced astigmatism.

Refractive surgeons, clever researchers, and inventive manufacturers will create improved techniques of refractive surgery that are adjustable enough to refine a patient's refraction many times after the initial surgery, thereby ensuring that the patient does not need to wear a distance optical correction. Synthetic procedures such as synthetic epikeratoplasty, intrastromal corneal rings, and phakic intraocular lenses are already heading in that direction. Flying spot lasers that can custom shape a cornea based on spacially resolved refractometry are on the horizon. Such new techniques should create better corneal contours, decrease optical aberrations, and improve patients' quality of vision.

These observations lead to two conclusions. First, as refractive surgeons succeed in developing better techniques to treat ametropias, we must not let our enthusiasm cloud clear vision of the goal: visual function equal to or better than that achieved with spectacles and contact lenses. Second, we must fulfill our obligation to communicate honestly and thoroughly with patients so they have realistic expectations about postoperative use of spectacles and postoperative quality of vision using current techniques.

REFERENCES

1. Werblin TH. 20/20- how close must we get? J Refract Surg 1997;13:300-301.

2. Bourque LB, Lynn MJ, Waring GO III, Cartwright C, Prospective Evaluation of Radial Keratotomy Study Group. Spectacle and contact lens wearing six years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy study. Ophthalmology 1994;100:421-431.

3. Waring GO HI, Lynn MJ, McDonnell PJ, PERK Study Group. Results of the Prospective Evaluation of Radial Keratotomy (PERK) study 10 years after surgery. Arch Ophthalmol 1994;112:1298-1308.

4. Lindstrom RL. Minimally invasive radial keratotomy: Mini-RK. J Cataract Refract Surg 1996;21:27-34.

5. Sawelson H, Marks RG. Ten year refractive and visual results of radial keratotomy. Ophthalmology 1995;1Q2:18921901.

6. Ellingsen KL, Nizam A, Ellingsen BA, Lynn MJ, Age-related refractive shifts in simple myopia. J Refract Surg 1997;13:223-228.

7. Nosé W, Neves RA, Burris TE, Schanzlin DJ, Belfort R. Intrastromal corneal ring: 12-month sighted myopic eyes. J Refract Surg 1996;12:20-28.

8. Baikoff G, JoIy P. Comparison of minus power anterior chamber intraocular lenses and myopic epikeratoplasty in phakic eyes. Refract Corneal Surg 1990;6:252-260.

9. Brown EVL. Net average yearly shifts in refraction in atropinized eyes from birth to beyond middle life. Arch Ophthalmol 1938;19:719-34.

10. Exford J. A longitudinal study of refractive trends after age forty. Am J Optom 1965;42:685-92.

11. Hirsch MJ. Changes in refractive state after the age of fortyfive. Am J Optom 1958;35:229-37.

12. Bucklers M. Changes in refraction during life. Brit J Ophthal 1953;37:587-92.

13. Applegate RA, Howland HC. Refractive surgery, optical aberrations, and visual performance. J Refract Surg 1997;13:295-299.

14. Oliver KM, Hemenger RP, Corbett MC, O'Brart DPS, Verma S, Marshall J, Tomlinson A. Corneal optical aberrations induced by photorefractive keratectomy. J Refract Surg 1997;13:246-254.

10.3928/1081-597X-19970501-04

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