Small Optical Zone RK

Small Optical Zone RK

An example of an RK procedure done by Dr Yair Karas in 1991

"Both slit-beam and photographic measurements yield accurate and reliable results that reflect the true pathologic achieved clear zone diameter following radial keratotomy surgery." Dr Grimmett, J Refract Surg 1998.

Dr Yair Karas states in his promotional video that corneal scars never change over time.

"RK is ophthalmology's thalidomide"

Keith Harrison, FCLSA, NCLE-AC as spoken to RKsurvivor

"In approximately 1990, the standard of care for clear zone diameter is a minimum of 3.0 mm. Clear zones smaller than that diameter are outside of the standard of care, because they can create central corneal irregularity that can be a material contributing cause to visual distortion and blurry vision."

Dr George O Waring III,

"Most other gurus decry the use of subnominal OZs and give cogent reasons for this prohibition. Which means that should you use them, you are on your own.  Under the circumstances, is applying such zones in your best interest?  How about the patient's?  The answer should be: It is not.   It does not pay to go to extremes —especially at your stage of development.  If you will take my advice, you will never take on that extreme.
Remember that drowning is intensely personal.  Case in point: subnominal surgical clear zones."

Dr Leo D Bores                                                                                                  Refractive Eye Surgery, second edition

"Performing radial keratotomy with an optical zone smaller than 3mm is risking the possibility of severe glare problems, and the risk of slight displacement of the optical zone becomes increasingly greater with smaller optical zones-therefore a minimum limit of 3mm is recommended."

Dr Spencer Thornton, Radial and Astigmatic Keratotomy - 1994

"An optical zone below 3 mm is undesirable because of added glare, plus the real risk of encroaching on the visual axis." 

Dr Irving Schwab, Refractive Keratoplasty - 1987

Complications of small clear-zone radial keratotomy

To review the postoperative outcome of patients with radial keratotomy who have clear-zone diameters below 2.75 mm.A retrospective review was performed of all patients with radial keratotomy who have clear-zone diameters less than 2.75 mm presenting for consultation from August 1993-September 1995. Preoperative records and surgical reports were reviewed, and a thorough ophthalmic examination was performed. A total of 37 eyes had a clear-zone size below 2.25 mm. Six eyes were excluded from subsequent analysis due to keratoconus. The remaining 31 eyes had an average clear-zone size of 1.5 mm (standard deviation, 0.4 mm; range, 0.9-2.2 mm). Postoperative morbidity included severe disabling glare in 31 (100%) of 31 eyes, contact lens intolerance in 19 (100%) of the 19 eyes fitted, Snellen visual acuity loss (> 2 lines) in 25 (81%) of 31 eyes, inability to drive at night in 11 (69%) of 16 patients, moderate to severe diurnal visual fluctuation in 21 (68%) of 31 eyes, refractive undercorrection by greater than 1 diopter in 16 (52%) of 31 eyes, loss of employment in 4 (25%) of 16 patients, polyopia in 5 (16%) of 31 eyes, refractive overcorrection by greater than 1 diopter in 3 (10%) of 31 eyes, and a retinal detachment attributable to pilocarpine use in 1 (3%) of 31 eyes.Using radial keratotomy clear-zone diameters smaller than 2.25 mm has a highcomplication rate and is unsafe. Small clear-zone radial keratotomy should be abandoned. Although this study was limited to clear zones less than 2.25 mm, the authors endorse current recommendations that the clear zone should be at least 3.0 mm in diameter.

Ophthalmology 1996 Sep; 103(9) :1348-56

Small Optical Zone (OZ)


As reasonably experienced corneal/refractive surgeons, we have watched with interest the renewed popularity of radial keratotomy, hexagonal keratotomy, and associated instructional refractive surgery courses. Radial keratotomy, when used appropriately, is an excellent procedure for correcting myopia.

In our opinion, however, it is of the utmost importance to alert the public and our colleagues to the dangers and complications associated with hexagonal (box, circular) keratotomy. This procedure is capable of improving uncorrected visual acuity but almost always, in our experience, results in irregular corneal astigmatism and a significant decrease in thequalify of best corrected vision.

Hexagonal keratotomy seems to have a risk/benefit ratio that does not justify its use.

For at least 10 years, American refractive surgeons nave known and reported that radial keratotomy with optical zones of 2.5mm or less also carry an enormous risk of causing intractable glare, irregular astigmatism, and the significant, permanent loss of quality of vision.

We believe that surgeons who attempt to justify such small optical zones on the basis of uncorrected visual acuity without appreciating the factors that affect the quality of vision are making grave mistake. There is no improved surgical technique or diamond blade currently being used that in anyway changes these issues. A general issue, however, of even greater significance than those specific issues mentioned above, has surfaced. The issue is this:

Should a surgeon perform surgery on a routine basis that he or she knows (or should know) has large chance of permanently reducing a patient's best corrected visual acuity by 1 to 2 lines of vision and reduce the quality of vision, evenif an informed consent for such procedure is obtained?

We believe that the answer to the issue stated above is an emphatic "no." A surgeon does not have the right to allow patients to elect to hurt themselves. No truly informed "informed consent" can be obtained about a defective surgical procedure that does significant, permanent damage.

It would be unthinkable that intraocular lens companies be allowed to produce IOLs that allowed only 20/40 visual acuity; surgeons have there responsibility to refrain from performing a surgery that produces a poor result a majority of the time,whether the consumer desires such surgery or not.

Many cataract/IOL surgeons may not realize that responsible refractive-surgeons have struggled for years to honestly inform patients of the potential risks involved with their surgery. Now that many cataract/IOL surgeons feel financial pressure to start radial keratotomy, it is shocking that some are willing to consider lowering the standards for refractive surgery, rather than performing surgery that meets the higher standard. Ophthalmology simply does not have an adequate surgical solution for every refractive error, yet.

We understand, and have been involved with, the often difficult and unpredictable path that a new product or proceduremust endure before it is accepted or rejected by each surgeon and patient. For us, hexagonal keratotomy has been given a fair chance and has proven itself to be a failure. Patients who have experienced overcorrection with radial keratotomy and are then treated with hexagonal keratotomy are especially prone to severe corneal complications. Similar problems accompany radial keratotomy with small optical zones.

We urge those ophthalmic surgeons performing, advocating, and teaching hexagonal keratotomy and radial keratotomy with optical zones of 2.50 mm and less to critically reevaluate their results and the responsibilities incumbent upon them.

LEE T. NORDAN, MD La Jolla, Calif 

W. ANDREW MAXWELL, MD, PhD Fresno, Calif

Refractive &Corneal Surgery Volume8 July/August 1992

Measurement of radial keratotomy clear zone diameters

Bascom Palmer Eye Institute. The University of Miami. School of Medicine. Florida 33418, USA.

BACKGROUND: To compare the accuracy of photographic measurements to slit-lamp measurements of radialkeratotomy clear zone diameters in order to develop an independent, objective, unbiased, and reproducible method ofverifying clinical observations. 

METHODS: Twenty-five patients (48 eyes) following radial keratotomy had matched slit-lamp and photographic measurements of the diameter of the central clear cornea between the ends of opposite radial incision pairs. Matched slit-beam, photographic, and pathologic observations were compared statistically. 

RESULTS: Two hundred fifty-four slit-lamp clear zone diameter measurements were obtained. In twenty instances (8%), the radial incision end-point could not be identified on the photograph. For the remaining 234 measurements, the mean slit-lamp clear zone diameter was statistically smaller than the photographic measurement by 0.03 mm (t-test, p = 2.2 x 10(-5)).The slit-lamp and photographic clear zone measurements were strongly positively correlated (Pearson r = 0.99. p < 1.0 x 10(-15)). Matched slit-lamp, photographic, and pathologic clear zone measurements (N=8) in one excised corneal button were not statistically different. 

CONCLUSIONS: For radial keratotomy clear zone diameters, slit-beam measurements and photographic caliper measurements yield indistinguishable results that are highly concordant over a wide range of diameters. Both slit-beam and photographic measurements yield accurate and reliable results that reflect the true pathologic achieved clear zone diameter following radial keratotomy surgery.

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