This chapter provides an overview of radial keratotomy (RK), describes our current method for performing this incisional procedure, and discusses the management of common complications associated with RK.

The first RK procedure in the United States was performed by Bores and co-workers in 1978.¹⁰ Subsequently, there has been substantial laboratory and clinical research, including technologic advances in ultrasonic pachymeters and diamond micrometer knives that have made the procedure more predictable. In 1980, the National Eye Institute funded the Prospective Evaluation of Radial Keratotomy (PERK), which attempted to assess the efficacy, safety, predictability, and stability of RK.¹¹ Four-, five-, and ten-year results have been published that have helped define the limits of the procedure as well as its risks and benefits.^12–15

Patients considering RK should have stable, nonprogressive myopia confirmed by examination of previous refractions. Contact lens wear must be discontinued before consideration of RK so that any possible corneal warpage associated with contact lens use can be detected. Slit lamp examination should reveal an essentially normal cornea. Patients with ocular conditions such as glaucoma or uveitis may be poor candidates for RK because the effects of these disorders on the outcome are not well defined. Individuals with systemic conditions that might affect corneal healing, including patients with connective tissue diseases, those with herpes simplex keratitis, or patients using systemic corticosteroids, may be unsuitable candidates for RK.^16,18,19

RK achieves the best uncorrected visual acuity in patients who have low to moderate myopia (-4.00 to -6.00 D).^12,20–22 Patients with higher degrees of myopia (-6.00 to -10.00 D) tend to have a more variable response to surgery. RK has corrected the refractive error in some patients with myopia of -8.00 to -10.00 D,^10,20–23 although the refractive errors of most eyes with this amount of myopia remain undercorrected.¹⁷ However, some patients with high myopia may welcome even partial reduction of their refractive error if this allows them to read comfortably without glasses. Other refractive corneal procedures are available, including excimer laser photorefractive keratectomy (PRK), keratomileusis, laser in-situ keratomileusis (LASIK), and intrastromal corneal rings. Some patients may be better candidates for one of the other procedures if their myopia is outside the range of RK.

Patients must understand that although nomograms for RK are based on averages for large numbers of procedures, the outcome of surgery cannot be precisely predicted for an individual eye. Additional refractive keratotomy incisions may be needed to achieve the desired result, and spectacles or contact lenses may still be required for best visual acuity, even after surgery. Patients should be informed that contact lens fitting may be more difficult after RK because of changes in corneal topography.²⁴ Candidates for RK must understand that the surgery does not alter the normal aging process of presbyopia, for which most persons require reading glasses after the age of 40 to 45 years. Some persons older than 40 may exchange dependence on distance spectacles for dependence on reading glasses after RK. In the PERK study at 10 years, 39% of patients older than 40 years required reading glasses for near work because of presbyopia.¹⁵

Patients with a specific occupational motivation must be certain that the correction of myopia by incisional keratotomy is acceptable to their employer. Some occupations or careers will exclude a person from participation because of prior RK.

1. The diameter of the central clear zone can be adjusted between 3 and 5.5 mm. The smaller the diameter of the central clear zone, the greater the degree of flattening achieved. A review of nomograms suggests that the largest central clear zone with any efficacy is 5.5 mm. RK incisions with an optical zone of 6 mm or greater have virtually no effect on the refractive error,²⁸ supporting the position that radial incisions of the midperipheral cornea are responsible for the principal mechanical effect of the procedure. Most incisional keratotomy procedures involve optical zones of 3 to 5 mm.
   
2. The number of incisions usually varies from two to eight. Placement of more than eight incisions is generally not warranted because these succeeding incisions have progressively less effect. Placement of four radial incisions achieves greater than 70% of the effect achieved with eight incisions. For this reason, several surgeons have recommended a staged approach to RK in an attempt to minimize overcorrection.
   
3. The greater the depth of the incision, the greater the degree of central flattening. Centrifugally placed incisions (American technique) incise the cornea from the optical zone outward toward the limbus. This provides greater safety with regard to unintended incisions crossing the clear optical zone; however, these incisions may have a variable depth and tend to have a beveled incision profile at the optical zone (Fig. 1). Incisions placed in a centripetal manner (Russian technique) incise the cornea from the limbal area toward the optical zone mark; these are deep incisions, but they carry the risk of inadvertently entering the clear optical zone (Fig. 2). Incisions made centripetally are often not perfectly straight because of the natural tendency of the knife to stray when cutting with the vertical edge. In an effort to consistently provide deep incisions without the risk of inadvertently entering the clear optical zone, a double-pass technique has been devised that offers the benefits of both the Russian and American techniques (Fig. 3).^29–31
   
4. Incisions do not need to be carried to the limbus to achieve a near maximal effect.³² Lindstrom²⁸ has shown that the effects are similar for radial incisions from a 3-mm clear zone carried to a 7- to 8-mm optical zone (mini-RK) (Fig. 4) and for those carried to an 11-mm optical zone (Fig. 5). In fact, a mean increase of only 7.7% was seen when incisions were extended from the 7- to 11-mm optical zone. Thus, doubling the length of the RK incision achieved an additional effect of only 7.7%. The advantage of the shorter incisions is that the structural integrity of the cornea is better maintained. This may minimize the more serious complications and side effects of RK, including persistent diurnal fluctuation, long-term refractive instability with progressive hyperopic shift, and the potential for traumatic rupture of the keratotomy scars.³³ Thus, the use of minimally invasive RK or mini-RK may retain the benefits of RK for most low to moderate myopes while significantly reducing the risks.²⁸
   

There are two patient variables that clearly affect the outcome^25–27,34:

1. The greater the degree of myopia, the smaller the optical zone required, the greater the number of incisions needed, and the greater the depth of incisions necessary to achieve full correction.
   
2. The greater the patient's age, the greater the effect achieved with an identical surgical technique.
   

Patients older than 30 years can be expected to have an increased effect of 1.5% to 2% per year compared with a 30-year-old, whereas patients younger than 30 years can be expected to have a lesser effect of 1.5% to 2% per year compared with a 30-year-old. There may be other patient characteristics that affect the results of surgery, but these are difficult to measure consistently. These variables include corneal curvature, preoperative intraocular pressure, gender, corneal thickness, corneal diameter, axial length of the globe, and ocular rigidity. Most studies show that male patients, high intraocular tension, larger corneal diameter, a thicker cornea, a flatter cornea, and a higher ocular rigidity tend to result in a greater effect. Although these minor factors usually neutralize one another, the surgeon should screen for patients at high risk of overcorrection or undercorrection. The classic over-responder is the presbyopic, ocular hypertensive man who has a large, thick, flat cornea. The classic under-responder is the very young woman with a low intraocular tension and a small, thin, steep cornea.

Good candidates for RK can be expected, on average, to obtain a full correction with no more than an eight-incision RK. Some patients may benefit from correction of anisometropia even if full correction of the myopia is not achieved. Intense counseling is performed and proper informed consent is obtained. The patient is advised that, for safety reasons, only one eye at a time will be operated on, beginning with the nondominant eye. The patient may elect to have the second (dominant) eye operated on at any time 2 or more weeks after the first eye. Only in select cases with special needs and proper informed consent is bilateral simultaneous surgery performed. For patients with low myopia in whom only one eye is to be operated on, the procedure is performed on the dominant eye.

The surgical goal for the nondominant eye is typically -0.50 to -1.50 D, depending on the patient's age. A slightly more myopic target is preferred in the pre-presbyopic or presbyopic patient. Patients who under-respond and are left more myopic than is desired may undergo enhancement procedures 2 weeks or more postoperatively in the undercorrected eye. Patients with mild residual myopia in the nondominant eye are counseled that this monovision result may be preferred long-term and are discouraged from enhancement surgery.

The dominant eye is usually operated on no earlier than 2 weeks after the first eye, and an adjustment in the power of the procedure is made based on the response in the first eye. If, for example, the patient is a 30-year-old, and a four-incision mini-RK with a central clear zone of 3 mm is performed, an end result of 3.50 D of refractive correction would be expected. If the patient achieves only 3.00 D, he or she is approximately an 85% responder, and an adjustment can be made to perform a more powerful procedure in the second eye.

The nomograms used in surgical planning for RK are shown in Appendix 1 (2-, 4-, 6-, and 8-incision MRK Nomograms 1 through 4). Patients with greater than 1.00 D of astigmatism may require combined radial and astigmatic keratotomy.

The knife is set at the optical zone and plunged deliberately and straight into the cornea until the footplates are firmly positioned against the cornea. The tip of the knife is pointed at the center of the crystalline lens. This is followed by a 1-second pause, and, with mild pressure (enough to keep the footplates firm on the eye), a continuous incision is made. The cornea should be slightly moist, but excess fluid should be removed from the limbal area and fornices. This enables the surgeon to immediately detect a perforation. The surgeon's goal is to maintain the blade perpendicular to the corneal surface at all times. While making the incision, the surgeon can follow the “ski tracks” made by the footplates as well as the actual incision to maintain perpendicularity. When completed, the full-depth incision should extend from the inside of the central optical zone mark to the outside of the 7- to 8-mm mark (Fig. 9). To accomplish this with the American technique, the knife tip is set at the inside edge of the central optical zone mark, thus cutting out the peripheral mark and achieving a full-depth cut from the central optical zone at least to the 7-mm optical zone (see Fig. 1). In periphery-to-central cutting (Russian technique), the knife is set just outside the 7- to 8-mm optical zone marker and extended centrally until the central optical zone mark is cut out (see Fig. 2). A small rotation of the knife at the end of the incision is performed such that the tip of the blade points toward the center of the human lens (see Fig. 3). The double-pass technique combines a center-to-periphery and a periphery-to-center cut.

The double-pass technique (using the Duotrac or Genesis procedure) requires a specially designed diamond knife whose vertical facet is sharpened only on the bottom 200 to 250 μm, making it incapable of cutting beyond the end of the radial incision during deepening of the most central portion of the incision. The tips of these “two-step” knives may be pointed or square. The square tip may minimize double incisions upon the pass back to the center. The pointed tip may be less likely to cause a macroperforation. To perform the double-cutting technique, the knife tip is set at the inside edge of the central optical zone mark. The incision is made peripherally until the footplates cross the 7- to 8-mm optical zone mark. The blade is then pushed centrally, deepening the incision until the blade can no longer be extended centrally. Because the vertical facet is sharpened only on the bottom 200 to 250 μm, the blunt portion restricts the blade from inadvertently entering the clear central zone while allowing the central portion of the incision to be uniformly deepened. Again, a small rotation of the knife at the end of the incision is performed, thus slightly undercutting the central optical zone (see Fig. 3).

In a four-incision RK, three incisions are usually made with the dominant hand. A right-handed surgeon incises the 10:30 position first, followed by the 7:30 position and then the 1:30 position. The 4:30 incision can be completed with the left hand. When performing four-incision RK, surgeons should strongly consider placing the incisions in an oblique orientation. When the pupil dilates at night, this configuration minimizes the amount of starburst or glare. If the patient squints, all of the oblique incisions will be covered by the eyelid; this may be especially helpful for night driving (Fig. 10).

When performing an eight-incision RK, the surgeon should make the incisions in an opposing fashion, such that if a significant perforation occurs requiring cessation of the procedure, induced astigmatism will be minimal. The sequence of incisions should be made such that the last incisions are made in the thin inferotemporal region where the cornea is thinnest and microperforation is most likely to occur.

Some RK surgeons advocate that all incisions be made with the dominant hand. The eye is fixated and the incisions are made in succession, first toward the surgeon and then 135° away, in an effort to exploit the natural movements of the wrist and fingers.²¹ The microscope is turned successively by 45° intervals and the procedure repeated until all the incisions have been made. By making repeated pairs of incisions toward the surgeon and 135° away, consistency of depth and pressure is better maintained. This approach also simplifies the procedure for the beginning RK surgeon.

Once the incision pattern is completed, no irrigation of the incision is required. Several drops of antibiotic-corticosteroid solution are placed on the eye. No patch or cycloplegic agents are used. Placement of one to two drops of a nonsteroidal anti-inflammatory agent such as diclofenac (Voltaren, Ciba Vision Ophthalmics) or ketorolac (Acular, Allergan Pharmaceuticals) before and immediately after surgery decreases postoperative pain. The antibiotic-steroid drops are used by all patients for 1 week. If at the 1-week visit the patient is overcorrected more than + 1.00 D, the antibiotic-steroid drops are discontinued and replaced by 5% NaCl and 0.5% pilocarpine four times daily for 4 to 8 weeks. If the patient is within ±1.00 D of the desired result, the drops are discontinued when they run out. If the patient is more than -1.00 D undercorrected, the antibiotic-steroid drops are continued four times daily for 4 to 8 weeks postoperatively.

OPERATIVE COMPLICATIONS

Corneal Perforation

Corneal perforation during RK may be identified as a microperforation in which a loss of one or two drops of aqueous humor is noted or as a macroperforation that is large enough to produce shallowing of the anterior chamber. Macroperforation usually requires termination of the procedure and possible closure of the perforation with suture. The PERK study reported a 2.3% microperforation rate; however, no cases required suturing or termination of the surgery.³⁵ This low perforation rate was accomplished by setting the diamond knife at 100% of the thinnest paracentral corneal thickness reading and using the American technique with center-to-limbus incisions. Most microperforations appear in the inferior and temporal cornea, where the cornea is relatively the thinnest; however, they may appear in any location of the cornea.^36–38 Prolonged dehydration intraoperatively, with resultant thinning of the cornea, can increase the incidence of corneal perforation.^36,39 Macroperforations occur with a frequency of 0% to 0.45%,^38,40–42 although one report had a macroperforation rate as high as 13%.⁴³

Complications of a microperforation or macroperforation include formation of a scar at the level of Descemet's membrane, damage to the corneal endothelium, iridocorneal adhesions if the anterior chamber remains flat, and laceration of the anterior lens capsule if the incision is continued in the presence of a shallow anterior chamber after perforation.⁴⁴

Keratotomy incisions have been shown to cause mild injury to the corneal endothelium.^45,46 Postkeratotomy endothelial cell density shows a decrease of less than 10% when measured centrally; however, a greater degree of endothelial cell injury is noted when corneal perforation occurs during RK.⁴⁷ Studies using specular microscopy have not shown a progressive decrease⁴⁸ in endothelial cell density or other abnormalities in endothelial cellular morphology in human eyes 1 year after RK.

Incisions should not cross the limbus, because this does not enhance the effect of the operation and causes bleeding into the wound.⁴⁹ Furthermore, incisions crossing the limbus may stimulate a vascularized limbal scar and enhance growth of neovascular vessels into the wound, particularly if the patient wears a soft contact lens.

POSTOPERATIVE COMPLICATIONS

Most patients experience pain, throbbing, or foreign-body sensation for 24 to 48 hours postoperatively and frequently require analgesics. Glare or starburst caused by scattering of light intraocularly occurs commonly for a few months after surgery.²⁰ Glare or starburst may persist for a year or more,^50,51 and in 9% of patients it may cause diminished vision, particularly at night or on hazy, bright days.³⁷

Epithelial inclusion cysts in the incisional scars were seen in 8.6% of PERK patients after 1 year,¹⁵ but these do not seem to affect the visual results. In most patients, the scars tend to fade years after the surgery as collagen remodeling takes place.⁵²

A visually insignificant, brown, stellate, epithelial iron line appears in most eyes after RK. In the PERK study, 81% of eyes had a stellate epithelial iron line 6 months postoperatively.⁵³ The iron line appears at the junction of the middle and inferior third of the cornea, with fingers extending from the ends of the incisions.

Anterior corneal epithelial basement membrane changes, similar to those seen in epithelial basement membrane dystrophy, are often observed after RK.⁵⁴ These changes tend to be transient, lasting less than 3 months in most eyes. They are infrequently associated with clinical symptoms or recurrent epithelial erosion.³⁵

Epithelial Ingrowth

A single case of epithelial ingrowth after RK has been reported.⁵⁵ It has been suggested that the surgeon should avoid injection of an irrigating stream through a perforation site to minimize the introduction of epithelial cells intraoperatively.⁴⁶

Endophthalmitis

Three published case reports^56–58 of endophthalmitis after RK revealed a strikingly similar course. All patients developed a small hypopyon 8 to 10 days postoperatively, and Staphylococcus epidermidis was cultured in all cases. All patients had excellent visual outcomes several months postoperatively. Cross and Head⁵⁹ listed nine unpublished cases of endophthalmitis that included virulent gram-negative organisms. Corneal perforation appears to be responsible for the introduction of the microorganism into the eye, either during or shortly after the surgical procedure. Thorough preoperative chemical preparation of the eye is imperative, strict adherence to sterile surgical technique is required, and postoperative antibiotics and careful follow-up are recommended. A topical 5% povidone-iodine solution has been shown to decrease the incidence of postoperative endophthalmitis, and it is recommended for the preoperative preparation of the surgical field.⁶⁰

Ptosis

Blepharoptosis is a reported complication of RK.^61,62 Because retrobulbar injections and superior rectus bridle sutures were not used in the cases reported, the most likely cause of blepharoptosis was damage to the levator aponeurosis by the eyelid speculum. It has been suggested that a gentle wire speculum might be less likely to induce ptosis than a solid, rigid eyelid speculum.⁶²

Keratitis

Bacterial or fungal keratitis can occur in the immediate postoperative period or can be delayed several years after refractive keratotomy. The incidence seems to be higher when soft contact lenses, especially extended-wear lenses, are used after RK. Several cases of bacterial keratitis have been reported; the causative organisms included Pseudomonas, Staphylococcus aureus, and S. epidermidis.^40,63 Prophylactic topical antibiotics are to be encouraged until re-epithelialization has occurred. Two cases of Mycobacterium chelonei keratitis were reported from the same surgeon's office; in these two cases, outpatient RK was performed with cold-sterilized instruments.⁶⁴

A most unusual complication of refractive keratotomy is the late development of bacterial and fungal ulcerative keratitis.^65–67 All infiltrates are noted to be contiguous with the keratotomy scars. The persistent epithelial plug in the keratotomy wound is implicated in delayed bacterial and fungal keratitis.⁶⁸

Traumatic Rupture of Keratotomy Incisions

Any corneal incision results in a scar that does not have the same tensile strength as the original cornea. This is true not only after incisional keratotomy but also after corneal transplantation or accidental trauma.⁶⁹ There are several reports of traumatic rupture of keratotomy scars after blunt trauma.^70–72 In a rabbit eye model, Larson and colleagues⁷³ observed that the blunt force required to rupture the globe after RK within 90 days of healing was approximately half that required to rupture control eyes, which did not have surgery. In a porcine eye model, Rylander and co-workers⁷⁴ demonstrated that ruptures occurred most frequently at the equator in normal, unoperated eyes, but they occurred through the keratotomy incisions in eyes that previously underwent RK. Pinheiro and associates³³ recently showed that, under laboratory conditions, rupture of mini-RK incisions occurs at much higher intraocular pressure than does rupture of standard RK incisions. The rupture pressures of these eyes with mini-RK incisions were no different than they were in eyes that had not had mini-RK.

REFRACTIVE COMPLICATIONS

The most frequently reported complication of RK is an inaccurate outcome. The principal complications include overcorrection, undercorrection, increased astigmatism, irregular astigmatism, a progressive postoperative shift toward hyperopia, and diurnal fluctuation of vision.

Diurnal Fluctuation

Many patients who have had RK report fluctuation of vision during the course of the day. In the PERK study,^75,76 patients who complained of fluctuating vision were examined twice on the same day, before 8 AM and after 7 PM. At 1 year, 42% of the eyes demonstrated a manifest refraction that changed from 0.50 to 1.25 D. At approximately 3.5 years after RK, 31% of eyes showed a change of 0.50 D or more during the course of the day. At 11 years after RK, 54% of eyes showed a change in refractive error of 0.50 D or more.⁷⁷ Thus, diurnal fluctuation may be a permanent sequela of RK in some individuals. Keratometry and refraction demonstrated that most of the corneas underwent a gradual steepening during the course of the day, which ranged from 0.50 to 1.25 D. Therefore, patients with undercorrected vision saw best in the morning, whereas patients whose vision was overcorrected experienced an increase in visual acuity during the day.^75,76

Although the exact cause of this diurnal fluctuation is unknown, it is most likely related to structural changes induced by the keratotomy incisions and scars. Corneal edema that occurs during sleep or contact lens wear has been shown to flatten the cornea after RK. The unsutured wounds in the avascular cornea may require more than 4 to 5 years to eject the epithelial plug completely and to remodel the corneal stroma adjacent to the incisional scar.^78–82 The constant pressure of the eyelids and mild epithelial and stromal edema during sleep are believed to induce a nocturnal flattening of the cornea.

Overcorrection

Consecutive hyperopia after RK may result from an initial overcorrection or from a continued effect of the procedure with time.¹⁶ Five-year follow-up of the PERK study showed that 22% of the eyes had a refractive change of 1.00 D or more in the hyperopic direction between 6 months and 5 years after RK. The refractive error was within 1.00 D of emmetropia for 64% of eyes in this group. However, 17% were hyperopic by more than 1.00 D.¹³ Between 6 months and 10 years after RK in the PERK study, 43% of eyes changed in the hyperopic direction by 1.00 D or more. The average rate of change was + 0.21 D per year between 6 months and 2 years and + 0.06 D per year between 2 and 10 years. Thus, progression toward hyperopia continues over time, with the greatest rate of change occurring in the first 2 years after RK.¹⁵ A progressive effect in the hyperopic direction has also been seen after two- to four-incision RK. In two different studies, 3.5% and 6.3% of patients were overcorrected more than 1.00 D 1 year after RK.^83,84 Because of the progressive effect of RK with time, many surgeons are now intentionally leaving patients slightly myopic. Also, many RK procedures are now staged such that two to four incisions are placed initially and additional incisions are added at some point in the future should they become necessary.

Overcorrection of the refractive error after RK can be managed by spectacles or, if anisometropia is present, contact lenses. Contact lens fitting after RK has its own unique problems. The flat central cornea and the relatively steeper paracentral cornea cause the contact lens to decenter as it moves across the paracentral point. Two studies have reported only 56% and 58% success rates in fitting rigid gas-permeable contact lenses after RK.^85,86 Neovascularization of perilimbal incisional scars has limited the fitting of RK patients with soft contact lenses.^85,86

Surgical management of overcorrection after RK has involved placement of a continuous pursestring suture⁸⁷ or placement of interrupted sutures.⁸⁸ Lindquist and colleagues⁸⁹ showed that opening of RK incisions followed by irrigation and closure with 10-0 nylon or Mersilene suture could induce central corneal steepening. Interrupted corneal sutures also allow for selective suture removal weeks after the procedure so that the residual astigmatism can be modified. A mean increase of central corneal steepening of 1.63 D was seen in those who had eight-incision RK. Intraoperative keratometry demonstrated that 70% of the central corneal steepening achieved at the time of suture placement decays with time. Therefore, significant overcorrection needs to be achieved intraoperatively because much of the effect will decay with time.⁸⁹

More recently, placement of a four-bite lasso-type suture without opening of incisions has been used (Fig. 11). This can be performed with 10-0 nylon or 11-0 polyester suture. Quicker visual recovery occurs when the incisions are not opened. Long-term results are not yet available on this method of management of overcorrection.

Induced Astigmatism

Five-year results of the PERK study revealed that 15% of eyes had an increase of astigmatism of 1.00 D or more postoperatively. The change in refractive astigmatism ranged from a decrease of 1.50 D to an increase of 4.50 D. Although the maximum allowable astigmatism for entry into the PERK study was 1.50 D, 15% of eyes had more than 1.50 D 5 years postoperatively.¹³

After RK, all corneas have some irregular astigmatism, which can be detected by keratoscopy. This is manifested where the regular, smooth, circular configuration of the inner mires overlying the optical clear zone contrasts with the slightly irregular configuration of the outer mires overlying the incisions.¹³ Minimal irregular astigmatism appears to have little visual effect under daylight conditions, presumably because it lies outside the optical clear zone. Under dim illumination, however, when the pupil dilates, more glare and distortion result. This has been reported as a “starburst” phenomenon. Significant irregular astigmatism can occur when incisions extend too close to the visual axis in eyes with repeated operations or in eyes whose radial and transverse (or radial and circumferential) incisions intersect.^14,17 Symptoms in patients with mild to moderate irregular astigmatism can be minimized by a rigid, gas-permeable contact lens.

CATARACT SURGERY

Planned extracapsular cataract surgery⁹⁰ and phacoemulsification³⁶ have been performed successfully after RK. Calculation of the intraocular lens power can be difficult because keratometric readings are not stable for many months, and sometimes for years, after RK.¹⁶

Conventional keratometry may tend to overestimate corneal power, because only four points at a 3-mm zone are measured. These points are near the mid-peripheral knee of the cornea, which is steeper than the more central portion of the cornea after RK. Points located centrally are not measured by a standard keratometer. Thus, the use of keratometric values derived from a conventional keratometer may result in selection of an intraocular lens of insufficient power, which contributes to postoperative hyperopia.⁹¹ Celikkol and associates⁹² have shown that keratometric values derived from computerized videokeratography may be more accurate in predicting intraocular lens power than keratometric values derived by traditional keratometry.

PENETRATING KERATOPLASTY

During corneal transplantation, the forces induced by trephination may pull the radial incisions apart, causing aqueous leaks at the junction of the separated radial incisions and the circular keratoplasty incision. Beatty and colleagues⁹³ have recommended closure of the radial incisions before corneal transplantation. Double-crossed, interrupted, and double-running antitorque suturing techniques were found to be the most effective in an eye bank eye model.⁹³ Rashid and Waring¹⁶ have recommended that an intrastromal pursestring suture be placed approximately 1.5 mm outside the intended trephination site to stabilize the radial incisions. This is particularly useful when a large number of incisions are present.

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30. Assil KK, Kassoff J, Schanzlin DJ et al: A combined incision technique of radial keratotomy. Ophthalmology 101:746, 1994

31. Verity M, Talamo JH, Choyet A et al: The combined (Genesis) technique of radial keratotomy: prospective, multicenter study.Ophthalmology 102:1908, 1995

32. O'Donnell FE: Short-incision radial keratotomy: a comparative study in rabbits. J Refract Surg 3:22, 1987

33. Pinheiro MN, Bryant MR, Tayyanipour R et al: Corneal integrity after refractive surgery: effects of radial keratotomy and mini-radial keratotomy. Ophthalmology 102:297, 1995

34. Rowsey JJ, Balyeat HD, Rabinovitch B et al: Predicting the results of radial keratotomy. Ophthalmology 90:642, 1983

35. Waring GO, Lynn MJ, Gelender H et al: Results of the Prospective Evaluation of Radial Keratotomy (PERK) study one year after surgery. Ophthalmology 90:642, 1983

36. Sanders DR, Hofmann RF, Salz JJ (eds): Refractive Corneal Surgery. Thorofare, NJ, Slack, 1986

37. Rowsey JJ, Balyeat HD: Preliminary results and complications of radial keratotomy. Am J Ophthalmol 93:437, 1982

38. Rowsey JJ, Balyeat HD: Radial keratotomy: preliminary report of complications. Ophthalmic Surg 13:27, 1982

39. Villaseñor RA, Salz J, Steel D, Krasnow MKA: Changes in corneal thickness during radial keratotomy. Ophthalmic Surg 12:341, 1981

40. Marmor RH: Radial keratotomy complications. Ann Ophthalmol 19:409, 1987

41. Sawelson H, Marks RG: Two-year results of radial keratotomy. Arch Ophthalmol 103:505, 1985

42. Shachar RA, Levy NS, Schachar L: Refractive Keratoplasty, pp 328–396. Deniston, TX, LAL Publishing, 1983

43. Schwab IR (ed): Refractive Keratoplasty, pp 227–272. New York, Churchill Livingstone, 1987

44. Grady FJ: Experience with radial keratotomy. Ophthalmic Surg 13:395, 1983

45. Hoffer KJ, Darin JJ, Pettit TH et al: Three years' experience with radial keratotomy: The UCLA study. Ophthalmology 90:627, 1983

46. MacRae SM, Matsuda M, Rich LF: The effects of radial keratotomy on the corneal endothelium. Am J Ophthalmol 100:538, 1985

47. Chiba K, Oak SS, Tsubota K et al: Morphometric analysis of corneal endothelium following radial keratotomy. J Cataract Refract Surg 13:263, 1987

48. Rowsey JJ, Balyeat HD, Monlux R et al: Endothelial cell loss after radial keratotomy. Ophthalmology 94:97, 1987

49. Ellis W: Radial Keratotomy and Astigmatism Surgery, pp 117–130. Irvine, CA, Keith C. Terry & Associates, 1986

50. Arrowsmith PN, Marks RG: Visual, refractive, and keratometric results of radial keratotomy: a two-year follow-up. Arch Ophthalmol 105:76, 1987

51. Dietz MR, Sanders DR, Marks RG: Radial keratotomy: an overview of the Kansas City study. Ophthalmology 91:467, 1984

52. Busin M, Yau CE, Yamaguchi T et al: The effect of collagen cross-linkage inhibitors on rabbit corneas after radial keratotomy. Invest Ophthalmol Vis Sci 27:1001, 1986

53. Cogan DG, Donaldson DD, Kuwabara T, Marshal D: Microcystic dystrophy of the corneal epithelium. Trans Am Ophthalmol Soc 62:213, 1982

54. Nelson JD, Williams P, Lindstrom RL, Doughman DJ: Map-finger-dot changes in the corneal epithelial basement membrane following radial keratotomy. Ophthalmology 92:199, 1985

55. Binder PS: Presumed epithelial ingrowth following radial keratotomy. CLAO J 12:247, 1986

56. O'Day DM, Feman SS, Elliott JH: Visual impairment following radial keratotomy: a cluster of cases. Ophthalmology 92:199, 1985

57. Gelender H, Flynn HW, Mandelbaum SH: Bacterial endophthalmitis resulting from radial keratotomy. Am J Ophthalmol 93:323, 1982

58. Manka RL, Gast TJ: Letter to the editor: Endophthalmitis following Ruiz procedure. Arch Ophthalmol 108:21, 1990

59. Cross WD, Head WJ: Complications of radial keratotomy: an overview. In Sanders D, Hofmann RG, Salz J (eds): Refractive Corneal Surgery, pp 347–399. Thorofare, NJ, Slack, 1986

60. Apt L, Isenberg SJ, Yoshimori R et al: The effect of povidone-iodine solution applied at the conclusion of ophthalmic surgery. Am J Ophthalmol 119:701, 1995

61. Carroll RP, Lindstrom RL: Blepharoptosis after radial keratotomy. Am J Ophthalmol 102:800, 1986

62. Linberg JV, McDonald M, Safir A, Googe JM: Ptosis following radial keratotomy: performed using a rigid eyelid speculum. Ophthalmology 93:1509, 1986

63. Lewicky A, Salz J: Special report: radial keratotomy survey. J Refract Surg 2:32, 1986

64. Robin JB, Beatty RF, Dunn S et al: Mycobacterium chelonei keratitis after radial keratotomy. Am J Ophthalmol 102:72, 1986

65. Cottingham AJ, Berkeley RG, Nordan LT et al: Bacterial corneal ulcers following keratorefractive surgery: A retrospective study of 14,163 procedures. Presented at the Ocular Microbiology and Immunology Group Meeting, San Francisco, September 28, 1986

66. Mandelbaum S, Waring GO, Forster RK et al: Late development of ulcerative keratitis in radial keratotomy scars. Arch Ophthalmol 104:1156, 1986

67. Shivitz IA, Arrowsmith PN: Delayed keratitis after radial keratotomy. Arch Ophthalmol 104:1153, 1986

68. Stern GA, Weitzenkorn D, Valenti J: Adherence of Pseudomonas aeruginosa to the mouse cornea: epithelial vs stromal adherence. Arch Ophthalmol 100:1965, 1982

69. Maurice DM: The biology of wound healing in the corneal stroma: Castroviejo lecture. Cornea 6:162, 1987

70. Binder PS, Waring GO, Arrowsmith PN, Wang CL: Traumatic rupture of the cornea after radial keratotomy. Arch Ophthalmol 106:1584, 1988

71. Forstot SL, Damiano RE: Trauma following radial keratotomy. Ophthalmology 94:127, 1987

72. Simmons KB, Linsalata RP: Ruptured globe following blunt trauma after radial keratotomy. Ophthalmology 94:148, 1987

73. Larson BC, Kremer FB, Eller AW, Bernardino VB: Quantitated trauma following radial keratotomy in rabbits. Ophthalmology 90:660, 1983

74. Rylander HG, Welch AJ, Fleming B: The effect of radial keratotomy in the rupture strength in rabbits. Ophthalmic Surg 14:744, 1983

75. Schanzlin DJ, Santos VR, Waring GO et al: Diurnal change in refraction, corneal curvature, visual acuity, and intraocular pressure after radial keratotomy in the PERK study. Ophthalmology 93:167, 1986

76. Waring GO, Lynn MJ, Culbertson W et al: Three-year results of the Prospective Evaluation of Radial Keratotomy (PERK) study. Ophthalmology 94:1339, 1987

77. McDonnell PJ, Nizam A, Lynn MJ et al: Morning-to-evening change in refraction, corneal curvature, and visual acuity eleven years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy study. Ophthalmology 103:233, 1991

78. Steinberg EB, Waring GO, Wilson LA: Slit-lamp microscopic study of corneal wound healing after radial keratotomy in the PERK study. Am J Ophthalmol 100:218, 1985

79. Ingraham HJ, Guber D, Green WR: Radial keratotomy: clinical pathologic case report. Arch Ophthalmol 103:683, 1985

80. Yamaguchi T, Tamaki K, Kaufman HE et al: Histologic study of a pair of human corneas after anterior radial keratotomy. Am J Ophthalmol 100:281, 1985

81. Binder PS, Nayak SK, Deg JK et al: An ultrastructural and histochemical study of long-term wound healing after radial keratotomy. Am J Ophthalmol 103(pt 2):432, 1987

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83. Salz JJ, Villaseñor RA, Elander R et al: Four-incision radial keratotomy for low to moderate myopia. Ophthalmology 93:727, 1986

84. Spigelman AV, Williams PA, Nichols BD, Lindstrom RL: Four-incision radial keratotomy. J Cataract Refract Surg 14:125, 1988

85. Hofmann RF, Starling JC, Masler W: Contact fitting after radial keratotomy. J Refract Surg 2:155, 1986

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2-Incision MRK Nomogram

HOW TO USE THIS NOMOGRAM

  Identify the patient's age and the diopters of refractive myopia that you wish to correct.
  Find the patient's age in the first column on the left.
  Move to right until you reach the surgery results closest to the refractive myopia of the patient. In order to avoid overcorrection, it is suggested that you select a surgical goal somewhat less than the actual refractive myopia. The column heading then tells you which surgery is needed to achieve this result.
  Consider placing the incisions on the steeper meridian when the patient has 0.75 to 1.50 diopters or more of astigmatism.

EXAMPLE

  A 45-year old patient with a refractive myopia of 1.75 and 1.00 diopters of astigmatism on the 90° axis.
  Moving to the right on the Age 45 line, you see that 1.75 falls between 1.76 and 1.56. Looking at the column headings, you see that a 2 incision × 3.75 mm length will correct 1.76 diopters of myopia. A 2 × 4.0 mm length will correct to 1.56 diopters of myopia.
  The recommendation in this case is to do a 2 × 4.0 mm incision. The astigmatism should be reduced to approximately 0.50 diopters.

4-Incision MRK Nomogram

HOW TO USE THIS NOMOGRAM

  Identify the patient's age and the diopters of refractive myopia that you wish to correct.
  Find the patient's age in the first column on the left.
  Move to right until you reach the surgery results closest to the refractive myopia of the patient. In order to avoid overcorrection, it is suggested that you select a surgical goal somewhat less than the actual refractive myopia. The column heading then tells you which surgery is needed to achieve this result.

EXAMPLE

  A 45-year old patient with a refractive myopia of 3.75.
  Moving to the right on the Age 45 line, you see that 3.75 falls between 3.90 and 3.25. Looking at the column headings, you see that a 4 incision × 3.25 mm length will correct to 3.90 diopters of myopia. A 4 × 3.5 mm length will correct 3.25 diopters of myopia.
  The recommendation in this case is to do a 4 × 3.25 mm incision.

6-Incision MRK Nomogram

HOW TO USE THIS NOMOGRAM

  Identify the patient's age and the diopters of refractive myopia that you wish to correct.
  Find the patient's age in the first column on the left.
  Move to right until you reach the surgery results closest to the refractive myopia of the patient. In order to avoid overcorrection, it is suggested that you select a surgical goal somewhat less than the actual refractive myopia. The column heading then tells you which surgery is needed to achieve this result.
  When the patient has with-the-rule astigmatism of 0.75 to 1.50 diopters and the operation is not combined with ARC-T, center 5th and 6th incisions on steeper meridian.

EXAMPLE

  A 45-year old patient with a refractive myopia of 3.75.
  Moving to the right on the Age 45 line, you see that 3.75 falls between 4.06 and 3.66. Looking at the column headings, you see that a 6 incision × 3.5 mm length will correct to 4.06 diopters of myopia. A 6 × 3.75 mm incision will correct 3.66 diopters of myopia.
  The recommendation in this case is to do a 6 × 3.75 mm incision.

8-Incision MRK Nomogram

HOW TO USE THIS NOMOGRAM

  Identify the patient's age and the diopters of refractive myopia that you wish to correct.
  Find the patient's age in the first column on the left.
  Move to right until you reach the surgery results closest to the refractive myopia of the patient. In order to avoid overcorrection, it is suggested that you select a surgical goal somewhat less than the actual refractive myopia. The column heading then tells you which surgery is needed to achieve this result.

EXAMPLE

  A 45-year old patient with a refractive myopia of 3.75.
  Moving to the right on the Age 45 line, you see that 3.75 falls between 3.90 and 3.41. Looking at the column headings, you see that an 8 incision × 4.0 mm length will correct 3.90 diopters of myopia. An 8 × 4.25 mm length will correct to 3.41 diopters of myopia.
  The recommendation in this case is to do an 8 × 4.25 mm incision.