Ординатура / Офтальмология / Английские материалы / Hyperopia and Presbyopia_Tsubota, Boxer Wachler, Azar_2003

two or three rings of eight spots, with 6-, 7-, and 8-mm-zone diameters. The mean spherical equivalent at 15 months was reduced to 1.73 0.16 D. In all, 57.8% of the eyes were1.00 D of intended correction, while 21% were 0.50 D of intended correction. Patients with 75 to 100% regression were compared to those with 25% or less regression. Full regression was more common in patients between 18 and 30 years of age, with an inverse correlation with increasing age. Gezer et al. reported 18% regression in patients older than 20 years and 48% in patients less than 20 years of age (48). Corneal thickness correlated directly with regression. Patients with central corneal thickness of 525 m or less experienced the least amount of regression. Average keratometry did not influence regression. Alio et al. hypothesize that the regression of effect might be due to the elasticity of Bowman’s membrane and stromal collagen in younger patients, or due to thicker corneas, allowing the cornea to return to its original shape. In addition, the thermal effectiveness of Ho:YAG LTK may depend on the water content of the corneal stroma, which may be age-dependent. Alio et al. have developed a formula for preoperative evaluation of the potential amount of postoperative regression: % of regression average keratometry x pachymetry/15 x age.

Since regression is common after Ho:YAG LTK, retreatment may be necessary. Nano and Muzzin conducted a study with 182 eyes with low hyperopia with mean preoperative spherical equivalent of 2.50 0.87 D (0.75 to 4.75 D) (49). At 12 months, the mean spherical equivalent was 1.25 0.96 D, with 45% regression in manifest refraction. Seventeen percent of the operated eyes were retreated (31 eyes). Eighteen (56%) eyes were retreated with Ho:YAG LTK, which has been reported to have a success rate between 50 and 70%. In the Sunrise LTK clinical trials, 85% of eyes were within 1.0 D of emmetropia after retreatment (50).

Excimer laser retreatment with laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) may also be performed after LTK. Nano and Muzzin treated 14 (45%) eyes with PRK (49). Portellinha et al. treated 12 eyes with hyperopic LASIK for residual hyperopia after LTK (51). The mean preoperative cycloplegic spherical equivalent refraction was 3.31 D (1.00 to 6.50 D). Postoperatively, all eyes achieved reduction in hyperopia to a mean postoperative refraction of 0.88 D. No morphological changes were observed in the radial thermal scars. Attia et al treated 50 eyes with hyperopic LASIK for regression after LTK (52). The mean spherical equivalent refraction improved from 2.92 1.60 D to 0.36 1.48 D; the predictability and efficacy were less than with primary LASIK for hyperopia. This study reported confluent haze between previous LTK spots in most eyes, as LASIK ablation took place at the sites of the LTK spots. The haze was greater when the LASIK flap cut coincided with the LTK spots. However, the corneal scarring did not seem to influence the visual results. Both studies conclude that LASIK after LTK is a good alternative for management of hyperopic regression.

3. LTK for PRK-Induced Hyperopia

Myopic treatment with PRK may result in a significant overcorrection in 2 to 5% of patients. Ho:YAG LTK has been evaluated for the correction of hyperopia induced by PRK (53–56). Alio et al. evaluated the use of noncontact Ho:YAG LTK in 14 eyes with hyperopia induced by PRK with a mean spherical equivalent of 4.20 1.80 D ( 1.75 to 6.25 D) (54). The Ho:YAG laser spots were applied outside the previous ablation zone to avoid confluence of haze. After 12-month follow-up, there was no difference between the mean preoperative spectacle-corrected visual acuity and the mean postopera-

tive uncorrected visual acuity. There was a mean increase of 4.60 1.20 D in central keratometric power. Contact Ho:YAG LTK was also evaluated for correction of hyperopia and astigmatism after PRK. Eggink et al. reported limited efficacy and predictability in 16 eyes treated with contact Ho:YAG LTK (55). However, there were no sight-threatening complications. Goggin and Lavery reported treatment of 11 eyes with mean preoperative spherical equivalent of 2.06 1.02 D and postoperatively to 0.511 0.55 D after 1-year follow-up. (56) a total of 91% were 20/40 or better and 82% were within 1.00 D of the target spherical equivalent.

4. LTK for LASIK-Induced Hyperopia

LASIK is a safe and effective technique for correction of moderate to high myopia. However, 2 to 8% of patients may have significant overcorrection (57). The efficacy and safety of noncontact Ho:YAG LTK for correction of hyperopia after LASIK was evaluated in 13 eyes (58). After 18 months of follow-up, the mean cycloplegic refraction changed from4.6 1.4 D ( 2.50 to 7.25 D) to 0.76 0.11 D. All of the patients were within1.50 D of emmetropia, and no patient lost lines of best-corrected visual acuity.

G. COMPLICATIONS

Mild pain, tearing, photophobia, and foreign-body sensation have been reported 1 to 3 days after surgery.(21,39,42,46,50) These complications were related to laser-induced epithelial injury, which resolved within 3 days in most patients. Opacities in each treatment spot decreased over time, becoming undetectable in most patients in room light; however, the opacities were observed with slit-lamp biomicroscopy even after 2 years (42). Astigmatism has been shown to be induced by Ho:YAG LTK, especially with the smaller treatment diameters (32,42,50). No significant changes in endothelial cell density occurred up to 12 months postoperatively (33,44). There was no significant loss of contrast sensitivity and no change in glare test measurements (33,46,50).

H. CONTINUOUS-WAVE DIODE LTK

Compared to pulsed Ho:YAG lasers, diode lasers provide continuous heat to the target tissue with more uniform stromal heating. This potentially allows for higher and more stable refractive correction. Wavelength settings of 1.854, 1.870, 1.885, and 2.1 m have been studied (59–63). The shorter wavelengths achieve greater corneal depth, with a wavelength of 1.854 m causing extensive local endothelial damage (0.8 to 1.2 mm in diameter) (61,62). A wavelength of 1.885 m has a penetration depth of 380 m, comparable to the absorption of the Ho:YAG laser emitting at 2.07- m wavelength. Continuouswave diode LTK has been tested in eight blind human eyes (63). A wavelength of 1.854 or 1.870 m with 100 to 150 mW power was applied for 10 s. The radiation was focused into the corneal stroma between 400 and 600 m or 1000 m with one or two eight-spot rings. The refractive change increased with higher laser power and smaller ring diameters. Two rings provided higher and more stable refractive effect of up to 5.66 D. The refractive effect stabilized between 3 and 6 months. Greater endothelial damage was noted with a wavelength of 1.854 m.

Ho:YAG LTK offers an alternative treatment for the correction of hyperopia up to2.50 D. There is an initial overcorrection followed by regression, dependent on age and

corneal thickness. Clinical studies have established the safety and efficacy of Ho:YAG LTK up to 2 years after treatment. LTK may also be used to treat PRK and LASIKinduced hyperopia. Diode lasers may help further improve stability of refractive effect with LTK. Wavefront-guided LTK may further improve the predictability of this procedure and allow for predictable outcomes even for retreatments of initial undercorrections.

REFERENCES

1.Lans LJ. Experimentelle Untersuchungen u¨ber Entstehung von Astigmatismus durch nichtperforirende Corneawunden. Graefes Arch Ophthalmol 1898; 45:117–152.

2.Terrien F. Dystrophie marginale symme´trique des deux cornee´s avec astigmatisme regulier consecutif et guerison par la cauterisation ignee. Arch Ophthalmol (Paris) 1900; 20:12–21.

3.Wray C. Case of 6 D of hypermetropic astigmatism cured by the cautery. Trans Ophthalmol Soc UK 1914; 34:109–110.

4.Gassett AR, Shaw EL, Kaufman HE, Itoi M, Sakimoto T, Ishii Y. Thermokeratoplasty. Trans Am Acad Ophthalmol Otolaryngol 1973; 77:OP–441–OP–454.

5.Shaw EL, Gassett AR. Thermokeratoplasty (TKP) temperature profile. Invest Ophthalmol Vis Sci 1974; 13:181–186.

6.Keates RH, Dingle J. Thermokeratoplasty for keratoconus. Ophthalm Surg 1975; 6:89–92.

7.Fogle JA, Kenyon KR, Stark WJ. Damage to epithelial basement membrane by thermokeratoplasty. Am J Ophthalmol 1977; 83:392–401.

8.Aquavella JV, Smith RS, Shaw EL. Alterations in corneal morphology following thermokeratoplasty. Arch Ophthalmol 1976; 94:2082–2085.

9.Arensten JJ, Rodrigues MM, Laibson PR. Histopathologic changes after thermokeratoplasty for keratoconus. Invest Ophthalmol Vis Sci 1977; 16:32–38.

10.Itoi M. Computer phtokeratometry changes following thermokeratoplasty. In: Schachar RA, Levy NS, Schachar L, eds. Refractive Modulation of the Cornea. Denison, TX: LAL Publishers, 1981:61–69.

11.Rowsey JJ, Doss JD. Preliminary report of Los Alamos Keratoplasty techniques. Ophthalmology 1981; 88:755–760.

12.Neumann AC, Fyodorov S, Sanders DR. Radial thermokeratoplasty for the correction of hyperopia. J Refract Corneal Surg 1990; 6:404–412.

13.Neumann AC, Sanders D, Raanan M, DeLuca M. Hyperopic thermokeratoplasty: clinical evaluation. J Cataract Refract Surg 1991; 17:830–838.

14.Neumann AC. Thermokeratoplasty for hyperopia. Ophthalmol Clin North Am 1992; 5: 753–772.

15.Feldman ST, Ellis W, Frucht-Perry J, Chayet A, Brown SI. Regression of effect following radial thermokeratoplasty in humans. J Refract Corneal Surg 1989; 5:288–291.

16.Beckman H, Fuller TA, Boyman R, Mandell G, Nathan LE Jr. Carbon dioxide laser surgery of the eye and adnexa. Ophthalmology 1980; 87:990–1000.

17.Peyman GA, Larson B, Raichand M, Andrews AH. Modification of rabbit corneal curvature with use of carbon dioxide laser burns. Ophthalm Surg 1980; 11:325–329.

18.Kanoda AN, Sorokin AS. Laser correction of hypermetropic refraction. In: Fyodorov SN, ed. Microsurgery of the Eye: Main Aspects. Moscow: MIR Publishers, 1987:147–154.

19.Horn G, Spears KG, Lopez O, Lewicky A, Yang XY, Riaz M, Wang R, Silva D, Serafin J. New refractive method for laser thermal keratoplasty with the Co:MgF2 laser. J Cataract Refract Surg 1990; 16:611–616.

20.Koch DD, Padrick TD, Menefee RL. Laser phtothermal keratoplasty: nonhuman primate results. Invest Ophthalmol Vis Sci 1992; 33(suppl):768.

21.Seiler T, Matallana M, Bende T. Laser themokeratoplasty by means of a pulsed holmium:YAG laser for hyperopic correction. J Refract Corneal Surg 1990; 6:335–339.

22.Durrie DS, Seiler T, King MC. Application of the holmium:YAG laser for refractive surgery. SPIE Proc 1992; 1644:56–60.

23.Stringer H, Parr J. Shrinkage temperature of eye collagen. Nature 1964; 204:1307.

24.Allain JC, Le Lous M, Cohen-Solal S, Bazin S, Maroteaux P. Isometric tensions developed during hydrothermal swelling of rat skin. Connect Tissue Res 1980; 7:127–133.

25.Koch DD. Histological changes and wound healing response following noncontact holmium: YAG laser thermal keratoplasty. Tr AM Ophth Soc 1996; 94:745–802.

26.Bakerman S. Distribution of the alphaand beta-components in human skin collagen with age. Biochim Biophys Acta (Amst) 1964; 90:621.

27.McCally RL, Bargeron CB, Green WR, Farrell RA. Stromal damage in rabbit corneas exposed to CO2 laser radiation. Exp Eye Res 1983; 37:543–550.

28.Smelser GK, Polack FM, Ozanics V. Persistence of donor collagen in corneal transplants. Exp Eye Res 1965; 4:349–354.

29.Lass JH, Ellison RR, Wong KM, Klein L. Collagen degradation and synthesis in experimental corneal grafts. Exp Eye Res 1986; 42:201–210.

30.Koch DD, Berry MJ, Vassiliadis A. Non-contact holmium:YAG laser thermal keratoplasty. In: Salz JJ, ed. Corneal Laser Surgery. Philadelphia: Mosby-Year Book, 1994:247–254.

31.Alio´ JL, Pe´rez-Santonja JJ. Correction of hyperopia by laser thermokeratoplasty (LTK). In: Agarwal S, Agarwal A, Pallikaris IG, Neuhann TH, Knorz MC, Agarwal A, eds. Refractive Surgery. New Delhi: Jaypee, 2000:583–591.

32.Cavanaugh TB, Durrie DS. Holmium YAG laser thermokeratoplasty: synopsis of clinical experience. Semin Ophthalmol 1994; 9(2):110–116.

33.Koch DD, Kohnen T, McDonnell PJ, Menefee RF, AAS, Berry MJ. Hyperopia correction by noncontact holmium: YAG laser thermal keratoplasty. United States phase IIA clinical study with a 1-year follow-up. Ophthalmology 1996; 103(10):1525–1535.

34.Tutton MK, Cherry PM. Holmium:YAG laser thermokeratoplasty to correct hyperopia: two years follow-up. Ophthalm Surg Lasers 1996; 27(5 suppl):S521–S524.

35.Eggink CA, Bardak Y, Cuypers MHM, Deutman AF. Treatment of hyperopia with contact Ho:YAG laser thermal keratoplasty. J Refract Surg 1999; 15(1):16–22.

36.Lim KH, Kim WJ, Wee WR, Shin DE, Lee JH, Chang BL. Holmium: YAG laser thermokeratoplasty for astigmatism in rabbits. J Refract Surg 1996; 12(1):190–193.

37.Hennekes R. Holmium:YAG laser thermokeratoplasty for correction of astigmatism. J Refract Surg 1995; 11(3 suppl):S358-S360.

38.Thompson V. Holmium: YAG laser thermokeratoplasty for correction of astigmatism. J Refract Corneal Surg 1994; 10:S293.

39.Ariyasu RG, Sand B, Menefee R, AAS, Hennings D, Rose C, Berry M, Garbus JJ, McDonnell PJ. Holmium laser themokeratoplasty of 10 poorly sighted eyes. J Refract Surg 1995; 11: 358–365.

40.Koch DD, Kohnen T, McDonnell PJ, Menefee RF, Berry MJ. Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty. United States phase IIA clinical study with a 1-year follow-up. Ophthalmology 1996; 103(10):1525–1535.

41.Kohnen T, Husain SE, Koch DD. Corneal topographic changes after noncontact holmium:YAG laser thermal keratoplasty to correct hyperopia. J Cataract Refract Surg 1996; 22:427–435.

42.Koch DD, Abarca A, Villarreal R, Menefee R, AAS, Kohnen T, Vassiliadis A, Berry M. Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty. Clinical study with two-year follow-up. Ophthalmology 1997; 104(11):1938–1947.

43.Kohnen T, Koch DD, McDonnell PJ, Menefee RF, Berry MJ. Noncontact holmium:YAG laser thermal keratoplasty to correct hyperopia: 18-month follow-up. Ophthalmologica 1997; 211: 274–282.

44.Vinciguerra P, Kohnen T, Azzolini M, Radice P, Epstein D, Koch DD. Radial and staggered treatment patterns to correct hyperopia using noncontact holmium:YAG laser thermal keratoplasty. J Cataract Refract Surg 1998; 24:21–30.

45.Koch DD, Kohnen T, Anderson JA, Binder PS, Moore MN, Menefee RF, AAS, Valderamma GL, Berry MJ. Histologic changes and wound healing response following 10-pulse noncontact holmium:YAG laser thermal keratoplasty. J Refract Surg 1996; 12:623–634.

46.Kohnen T, Villarreal V, R, Menefee R, Berry M, Koch DD. Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty: five-pulse treatments with 1 year follow-up. Graefes Arch Clin Exp Ophthalmol 1997; 235:702–708.

47.Alio´ JL, Ismail MM, Sanchez Pego JL. Correction of hyperopia with non-contact Ho:YAG laser thermal keratoplasty. J Refract Surg 1997; 13(1):17–22.

48.Gezer A. The role of patient’s age in regression of holmium:YAG thermokeratoplasty-induced correction of hyperopia. Eur J Ophthalmol 1997; 7(2):139–143.

49.Nano HD, Muzzin S. Noncontact holmium:YAG laser thermal keratoplasty for hyperopia. J Cataract Refract Surg 1998; 24:751–757.

50.Aker AB, Brown DC. Hyperion laser thermokeratoplasty for hyperopia. Int Ophthalmol Clin 2000; 40(3):165–181.

51.Portellinha W, Nakano K, Oliveira M, Simoceli R. Laser in situ keratomileusis for hyperopia after thermal keratoplasty. J Refract Surg 1999; 15(2 suppl):S218–S220.

52.Attia W, Pe´rez-Santonja JJ, Alio´ JL. Laser in situ keratomileusis for recurrent hyperopia following laser thermal keratoplasty. J Refract Surg 2000; 16:163–169.

53.Pop M. Laser thermal keratoplasty for the treatment of photorefractive keratectomy overcorrections: a 1-year follow-up. Ophthalmology 1998; 105(5):926–931.

54.Alio´ JL, Ismail MM, Artola A, Pe´rez-Santonja JJ. Correction of hyperopia induced by photorefractive keratectomy using non-contact Ho:YAG laser thermal keratoplasty. J Refract Surg 1997; 13:13–16.

55.Eggink CA, Meurs P, Bardak Y, Deutman AF. Holmium laser thermal keratoplasty for hyperopia and astigmatism after photorefractive keratectomy. J Refract Surg 2000; 16:317–322.

56.Goggin M, Lavery F. Holmium laser thermokeratoplasty for the reversal of hyperopia after myopic photorefractive keratectomy. Br J Ophthalmol 1997; 81:541–543.

57.Pe´rez-Santonja JJ, Bellot J, Claramonte P, Ismail MM, Alio´ JL. Laser-in-situ keratomileusis to correct high myopia. J Cataract Refract Surg 1997; 23:372–385.

58.Ismail MM, Alio´ JL, Pe´rez-Santonja JJ. Noncontact thermokeratoplasty to correct hyperopia induced by laser-in-situ keratomileusis. J Cataract Refract Surg 1998; 24:1191–1194.

59.Bende T, Jean B, Oltrup T. Laser thermal keratoplasty using a continuous wave diode laser. J Refract Surg 1999; 15:154–158.

60.Brinkmann R, Koop N, Geerling G, Kampmeier J, Borcherding S, Kamm K, Birngruber R. Diode laser thermokeratoplasty: application strategy and dosimetry. J Cataract Refract Surg 1998; 24(9):1195–1207.

61.Koop N, Wirbelauer C, Tu¨ngler A, Geerling G, Bastian GO, Brinkmann R. Thermal damage to the corneal endothelium in diode laser thermokeratoplasty. Ophthalmologe 1999; 96(6): 392–397.

62.Wirbelauer C, Koop N, Tu¨ngler A, Geerling G, Birngruber R, Laqua H, Brinkmann R. Corneal endothelial cell damage after experimental diode laser thermal keratoplasty. J Refract Surg 2000; 16:323–329.

63.Geerling G, Koop N, Brinkmann R, Tu¨ngler A, Cand med.m, Wirbelauer C, Birngruber R, Laqua H. Continuous-wave diode laser thermokeratoplasty: first clinical experience in blind human eyes. J Cataract Refract Surg 1999; 25:32–40.

Figure 2 The CK Keratoplast tip shown next to a 7–0 suture. (Courtesy of Refractec, Inc., Irvine, CA.)

current increases with increasing dehydration of collagen, the process tends to be selflimiting. A thermal model predicts a cylindrical footprint approximately 150 to 200 m wide by 500 m deep that extends to approximately 80% of the depth of the mid-peripheral cornea at each treated spot (36). Striae form between the treated spots, creating a band of tightening that increases the curvature of the central cornea, thereby decreasing hyperopia. The Hyperion noncontact LTK technique, on the other hand, applies heat directly to the surface of the cornea, heating tissue in a gradient, and generates a conical footprint (10).

B. THE CONDUCTIVE KERATOPLASTY PROCEDURE

1. The Conductive Keratoplasty Device

The Viewpoint CK system consists of a radiofrequency energy-generating console, a handheld, reusable, pen-shaped handpiece attached by a removable cable and connector, a speculum (choice of two, Lancaster or Barraquer) that provides a large surface for an electrical return path, and a pedal that controls release of radiofrequency energy. Attached to the handpiece is the Keratoplast tip, a single-use, disposable, stainless steel penetrating tip, 90 m in diameter and 450 m long, that delivers the current directly to the corneal stroma. At the very distal portion of the tip is a Teflon-coated stainless-steel stop that assures correct depth of penetration.

2. Patient Selection

a. Suitable Patients

Patients suitable for treatment with the Viewpoint CK System should have 0.75 to 3.00 D of spherical hyperopia and 0.75 D of refractive astigmatism. Visual acuity should be correctable to at least 20/40 in both eyes. Hard or rigid gas-permeable lenses should be

discontinued for at least 3 weeks and soft lenses for at least 2 weeks prior to the preoperative evaluation. Wearers of hard contact lenses should have two central keratometry readings and two manifest refractions taken at least 1 week apart. The manifest refraction measurements must not differ from the earlier measurements by more than 0.50 D in either meridian. Keratometry mires must be regular.

b. Unsuitable Patients

Patients with a peripheral pachymetry reading at the 6-mm optical zone of less than 560m are not suitable for treatment with the Viewpoint CK System. Also unsuitable are those who have had strabismus surgery; have anterior segment pathology; have residual, recurrent, active ocular or uncontrolled eyelid disease or any corneal abnormality; or have signs of progressive or unstable hyperopia. Other relative contraindications are a history of herpes zoster keratitis, herpes simplex keratitis, glaucoma, a history of steroid-respon- sive rise in intraocular pressure (IOP), a preoperative IOP 21 mmHg, or narrow angles. Patients with diabetes, diagnosed autoimmune disease, connective tissue disease, an immunocompromised state, current treatment with chronic systemic corticosteroid or other immunosuppressive therapy that may affect wound healing; a history of keloid formation; intractable keratoconjunctivitis sicca; or pregnancy are also contraindicated to receive the CK treatment.

3. Examinations

Preoperative examinations should include a manifest and cycloplegic refraction, an uncorrected and best spectacle-corrected visual acuity (distance and near), a slit-lamp and fundoscopic examination, applanation tonometry, central keratometry, ultrasonic pachymetry, and computed corneal topography.

4. Performing the CK Procedure

Correct the patient’s full cycloplegic spectacle refraction. Administer one drop of topical anesthetic three times at 5-min intervals and monitor the patient for degree of anesthesia. Do not use pilocarpine. Insert the CK lid speculum to provide corneal exposure and act as an electrical return path. Do not use a lid drape, for it may prevent direct contact of the lid speculum and eyelid, which would disrupt the electrical current return path. Tape the fellow eye closed. Position the operating microscope or slit-lamp biomicroscope over or in front of the eye to be treated.

Mark the cornea with the CK marker, and remind the patient to fixate on the light from the microscope. Dampen the CK marker with gentian violet or rose bengal stain. Center the marker’s cross hairs over the center of the pupil and apply light pressure on the marker to make a circular mark with eight intersections on the cornea. If using gentian violet, irrigate with balanced salt solution to remove excess ink. Dry the surface of the cornea thoroughly with a fiber-free sponge to avoid dissipation of applied energy by a wet surface.

Set the appropriate treatment parameters on the console according to the nomogram (Table 1). The default setting for treatment is 350 kHz, 60% power (0.6 W) for 0.6 s. Inspect the Keratoplast tip under the microscope to ensure it is not damaged or bent prior to application. When treating 0.75 to 0.875 D of hyperopia (eight spots), treat only at the 7-mm optical zone, beginning treatment at the 12 o’clock position and continuing in the sequence shown in Figure 3. When treating higher levels of hyperopia, follow the nomo-

CK—Conductive Keratoplasty

gram and application sequence. For example, for treating 1.00 to 1.625 D of hyperopia, apply a total of 16 spots: 8 spots at the 6-mm optical zone and 8 at the 7-mm optical zone. Begin application at each of these optical zones at the 12 o’clock position and continue in sequence until the full circle of spots has been completed. For treating 1.75 to 2.25 D, apply treatment at the 6-, 7-, and 8-mm optical zones for a total of 24 spots. For treating 2.375 D to 3.00 D, apply treatment to the 6-, 7-, and 8-mm optical zones and then to each of the eight sectors between the previously treated spots at the 7-mm optical zone for a total of 32 spots.

To treat each spot, place the tip of the delivery probe at the treatment mark on the cornea, perpendicular to the corneal surface. Apply light pressure until the tip penetrates the cornea down to the insulator stop. Depress the foot pedal to apply the radio frequency energy. A tone will sound as the energy is applied. At each treatment spot, keep the tip in place until the preprogrammed treatment time has been completed (the tone stops). Clean the tip with a fiber-free sponge after each treatment spot to remove any tissue debris,

Figure 3 Number, location, and sequence of treatment spots. (Courtesy of Refractec, Inc., Irvine, CA.)