Journal of Refractive Surgery

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HYPEROPIA 

Five Techniques for Improving Outcomes of Hyperopic LASIK

Roberto Zaldivar, MD; Susana Orcherow, MD; Harkaran S Bains

Abstract

ABSTRACT

PURPOSE: To determine whether five changes to our hyperopic LASIK protocol produced better outcomes.

METHODS: Five changes, both technical and surgical, were instituted for the treatment of hyperopia. These five changes were nomogram refinements accounting for accommodation, use of a 7.0-mm optical zone and a 9.5-mm transition zone, a targeted mean flap diameter of 10.5 mm, sequential interruption of the laser ablation, and cleaning of the interface. The study comprised 43 eyes undergoing LASIK for hyperopia or hyperopic astigmatism with a mean preoperative spherical equivalent refraction of +2.28 diopters (D), a mean sphere of +1.93 D (range: +4.25 to +0.25 D), and mean cylinder of +1.10 D (range: +4.50 to +0.25 D). The NIDEK CXII excimer laser was used for all treatments.

RESULTS: From 1 day to 3 months postoperatively, the mean hyperopic shift was <0.50 D. Postoperatively, the number of patients achieving a distance best spectacle-corrected visual acuity (BSCVA) of 20/20 gradually increased to 93% by 3 months. The number of eyes that achieved 20/15 increased by 11.7% compared to preoperatively. Eighty-eight percent of eyes maintained or gained lines of BSCVA. Four patients lost 1 line of BSCVA. One patient lost >1 line of vision due to visually significant microstriae.

CONCLUSIONS: The outcomes support the observation that five surgical and technical modifications to the hyperopic LASIK procedure result in excellent visual quality and refractive outcomes and a low rate of regression. [J Refract Surg. 2005;21(Suppl):S628-S632.]

Abstract

ABSTRACT

PURPOSE: To determine whether five changes to our hyperopic LASIK protocol produced better outcomes.

METHODS: Five changes, both technical and surgical, were instituted for the treatment of hyperopia. These five changes were nomogram refinements accounting for accommodation, use of a 7.0-mm optical zone and a 9.5-mm transition zone, a targeted mean flap diameter of 10.5 mm, sequential interruption of the laser ablation, and cleaning of the interface. The study comprised 43 eyes undergoing LASIK for hyperopia or hyperopic astigmatism with a mean preoperative spherical equivalent refraction of +2.28 diopters (D), a mean sphere of +1.93 D (range: +4.25 to +0.25 D), and mean cylinder of +1.10 D (range: +4.50 to +0.25 D). The NIDEK CXII excimer laser was used for all treatments.

RESULTS: From 1 day to 3 months postoperatively, the mean hyperopic shift was <0.50 D. Postoperatively, the number of patients achieving a distance best spectacle-corrected visual acuity (BSCVA) of 20/20 gradually increased to 93% by 3 months. The number of eyes that achieved 20/15 increased by 11.7% compared to preoperatively. Eighty-eight percent of eyes maintained or gained lines of BSCVA. Four patients lost 1 line of BSCVA. One patient lost >1 line of vision due to visually significant microstriae.

CONCLUSIONS: The outcomes support the observation that five surgical and technical modifications to the hyperopic LASIK procedure result in excellent visual quality and refractive outcomes and a low rate of regression. [J Refract Surg. 2005;21(Suppl):S628-S632.]

In the past two decades, a variety of surgical methods have attempted to successfully treat hyperopia. These techniques include lensectomy, Holmium laser, intracorneal lenses, photorefractive keratectomy (PRK), LASIK, and wavefront-guided LASIK. Laser in situ keratomileusis and PRK are currently the most common surgical interventions for treating low to moderate hyperopes. Excimer laser treatment of hyperopia uses an algorithm that delivers the ablation to the midperiphery of the cornea to increase corneal curvature. These algorithms create prolate or hyper-prolate corneas postoperatively, which is in contrast to the oblate shape induced by a myopic ablation. The correction of hyperopia using LASIK has shown inconsistent results compared to myopia.1 Hyperopia treatments are generally considered less predictable than myopic treatments.2

As the population ages, hyperopic LASIK is increasingly becoming more prominent. In certain parts of the world, hyperopic and mixed astigmatic treatments have grown steadily to account for approximately half of all LASIK procedures (Fig 1). As the number of cases of hyperopic LASIK increases, so does the potential for patient dissatisfaction with hyperopic LASIK compared to myopic LASIK. In this study, we explored methods to improve the results obtained with hyperopic LASIK.

PATIENTS AND METHODS

The aim of this study was to determine whether technical and surgical changes would enhance hyperopic outcomes. All observations are based on personal experience with the treatment of hyperopia for >20 years (R. Z.). Five different changes to our LASIK protocol, both surgical and technical, were identified and initiated. The five steps were consistently incorporated into all hyperopic LASIK treatments. The five steps included:

Figure 1. Percent of myopic versus hyperopic LASIK procedures performed by Roberto Zaldivar, MD, from 2001 to 2004.

Figure 1. Percent of myopic versus hyperopic LASIK procedures performed by Roberto Zaldivar, MD, from 2001 to 2004.

2) The optical zone was increased from 5.5 mm to 7.0 mm along with the incorporation of a proprietary aspheric laser ablation algorithm. Both modifications involved software and hardware changes incorporated into the NIDEK CXII excimer laser system (NIDEK, Gamagori, Japan) by a field service engineer.

3) The flap size was increased by changing from a 9.0-mm suction ring to a 10. 5 -mm suction ring for the NIDEK MK-2000 keratome.

4) All hyperopic laser ablations were interrupted by the surgeon (R.Z.) after every 8 seconds of treatment.

5) During the sequential stops outlined in number 4, a beaver blade was used to clean the stromal surface of interface debris.

Figure 2. Hyperopic LASIK nomogram for patients aged 20 to 35 years.Figure 3. Hyperopic LASIK nomogram for patients aged 35 to 45 years.

Figure 2. Hyperopic LASIK nomogram for patients aged 20 to 35 years.

Figure 3. Hyperopic LASIK nomogram for patients aged 35 to 45 years.

Patients were eligible for hyperopic LASIK if they were between 20 and 45 years old and had hyperopia between +0.25 to +4.50 diopters (D) with or without astigmatism up to +4.50 D. Forty-three eyes underwent LASIK for hyperopia or hyperopic astigmatism with the NIDEK CXII excimer laser and the NIDEK MK-2000 keratome. All surgeries were performed by one surgeon (R.Z.). Preoperatively, the mean spherical equivalent refraction was +2.28 D, mean sphere was + 1.93 D (range: +4.25 to +0.25 D), and mean cylinder was +1.10 D (range: +4.50 to +0.25 D). All patients underwent a comprehensive baseline ophthalmic evaluation that included visual acuity measurement, manifest and cycloplegic refractions, anterior segment examination, corneal topography, and a dilated fundus examination. Postoperatively, patients were examined at 1 day, 1 month, and 3 months. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, epithelial ingrowth, and interface characteristics were noted. At all evaluations, videokeratography was performed to evaluate the effective optical zone size and centration.

Table

TABLEValues Corresponding to Figure 4 for Change in Mean Sphere, Mean Cylinder, and Mean Spherical Equivalent Refraction Over TimeFigure 5. Number of patients with distance BSCVA of 20/20 preoperatively and distance UCVA of 20/20 postoperatively.

TABLE

Values Corresponding to Figure 4 for Change in Mean Sphere, Mean Cylinder, and Mean Spherical Equivalent Refraction Over Time

Figure 5. Number of patients with distance BSCVA of 20/20 preoperatively and distance UCVA of 20/20 postoperatively.

RESULTS

At 1 day postoperatively, the initial myopic shift in spherical equivalent refraction was -0.27 D (Table). At 1 month, the spherical equivalent refraction regressed to 0.01 D and by 3 months it was +0.13 D (Fig 4). By 3 months postoperatively, <0.50 D of regression had occurred compared to postoperative day 1.

At 3 months, 28 (65.11%) eyes had a distance UCVA of ≥20/20 (Fig 5). Figure 6 shows a comparison of the number of eyes that had a distance BSCVA of ≥ 20/20 preoperatively and those which achieved a distance BSCVA of ≥20/20 postoperatively. Postoperatively, 40 (93%) eyes gradually achieved a distance BSCVA of 20/20 by 3 months (see Fig 6). Preoperatively, 55.8% of eyes had a distance BSCVA of 20/15 and at 3 months postoperatively, the number of eyes that achieved 20/15 increased by 11.7% (Fig 7). Compared to preoperatively, 88% of eyes maintained or gained lines of BSCVA. Four patients lost 1 line of BSCVA. One lost >1 line of vision due to visually significant (Fig 8).

Figure 4. Change in mean sphere, mean cylinder, and mean spherical equivalent refraction over time.Figure 6. Number of patients with distance BSCVA of 20/20 preoperatively and distance BSCVA of 20/20 postoperatively.Figure 7. Number of patients with distance BSCVA of 20/15 preoperatively and distance BSCVA of 20/15 postoperatively.

Figure 4. Change in mean sphere, mean cylinder, and mean spherical equivalent refraction over time.

Figure 6. Number of patients with distance BSCVA of 20/20 preoperatively and distance BSCVA of 20/20 postoperatively.

Figure 7. Number of patients with distance BSCVA of 20/15 preoperatively and distance BSCVA of 20/15 postoperatively.

Figure 8. Loss and gain of distance BSCVA.

Figure 8. Loss and gain of distance BSCVA.

DISCUSSION

The treatment of hyperopia using an excimer laser a long history with only mild to moderate success compared to myopic treatment modalities. The iniuse of optical zones as small as 4 mm has been shown to result in poor refractive outcomes and has subsequently been abandoned.3 Additionally, as the optical zone size is reduced, the risk of decentration increased. In our early experience with use of small optical zones for PRK for hyperopia and myopia, we a tendency towards increased epithelial hyperplasia and fibrosis and a loss of refractive effect due this healing response. In LASIK, the use of small optical zones also promotes epithelial hyperplasia, but minimal risk of fibrosis. However, a loss of the reeffect still occurs. With the advent of increased optical zone sizes, the outcomes were vastly improved and the risk of epithelial hyperplasia and decentration decreased.

In this study, we present outcomes after incorporatfive changes to our hyperopic LASIK protocol that believed would increase the safety and efficacy of LASIK. Young hyperopes aged between 20 and 35 years represent the most difficult patient poputo effectively treat with hyperopic LASIK due accommodation. By accounting for the accommodaeffect using a nomogram based on a combination of manifest and cycloplegic refraction and adjusting for age, we were able to provide 20- to 35-year-old hyperopes with functional distance vision for many years to come. For example, in Figure 2, if the nomogram calculations were based solely on manifest refraction, the patient could likely become hyperopic within 1 to 2 years as accommodation diminishs with age. Alternately, if the nomogram calculations were based entirely on the cycloplegic refraction, the patient would be myopic almost immediately and for years to come. Most people do not perform daily living tasks under cycloplegia, hence we advocate the use of both manifest and cycloplegic refraction in nomogram calculations to address the accommodative effect in hyperopes.

Figure 9. Postoperative hyperopic LASIK corneal topography map shows a large effective optical zone and well-centered ablation.

Figure 9. Postoperative hyperopic LASIK corneal topography map shows a large effective optical zone and well-centered ablation.

The second modification involved the use of increased optical zone sizes and an aspheric laser profile. As stated previously, the use of increased optical zone sizes decreases the risk of epithelial hyperplasia and decentrations. The use of aspheric ablation profiles reduces the abrupt curvature changes between the optical and transition zones and untreated corneas that were created by the ablation algorithms of different excimer lasers. The reduced curvature changes tend to decrease the magnitude of hyperplasia and reduce the risk of regression. The use of large optical zone sizes and aspheric algorithms also increase the effective optical zone postoperatively (Fig 9). Large effective optical zones can reduce the risk of halos and glare postoperatively.

The use of larger treatment zones necessitates the creation of a large diameter keratectomy to encompass the entire treatment zone and reduce the risk of epithelial ingrowth. The routine use of a 10.5-mm keratectomy ring was, in fact, our third modification. A small diameter flap causes the ablation to be partially delivered to the edge of the keratectomy impinging on the epithelial surface. This causes epithelial cells to either slough off or become imbedded in the stromal-epithelial edge of the flap, causing epithelial nests.4,5 Fibrosis can occur at the border of the flap due to an ablation of the stromal-epithelial edge, which can also stimulate epithelial ingrowth. The ablation of the hinge may also occur if the flap is not of an adequate diameter, inducing aberrations. This issue may be more important with the use of spot lasers. The incidence of epithelial ingrowth is significantly greater with spot lasers compared to scanning slit lasers due to lack of control over spot placement.4,5 We advocate the use of large diameter keratectomy for hyperopia using a 10.5-mm suction ring (MK-2000, NIDEK). In low hyperopes, the risk of cutting corneal pannus, causing blood on the stromal surface, is less with a 10.5-mm ring size. Most low hyperopes are not contact lens users or are intermittent contact lens users compared to myopes who consistently wear or overwear contact lenses. We routinely use a 10.5-mm suction ring with the NIDEK MK-2000 keratome. In our experience, only 1% of our hyperopic patient population has had to undergo LASIK with a keratectomy ring diameter < 10.5-mm.

The fourth and fifth modifications were the sequential interruption of ablation after every 8 seconds of treatment and the cleaning of the interface during these stops, respectively. Laser ablations for hyperopia (and high myopia) have a thermal effect and produce interface debris regardless of plume evacuation. In this study, despite the use of a plume evacuator, interface debris was still noted. Interface debris has been reported 5 years after LASIK in a variety of excimer laser platforms.6 This represents molecular tissue debris that is being created during the ablation and deposited back onto the interface with a subsequent inflammatory reaction. The heat generated during ablation can reduce the refractive effect. The sequential stops in hyperopic treatments allow for dissipation of heat. Other investigators have reported beneficial effects of reducing the corneal temperature prior to laser ablation to account for the thermal effect.7 Although phototherapeutic keratectomy (PTK) may be an option to clean the interface, it is a surgeon-dependent technique. Also the laser ablation in PTK has the potential to create more debris. We found that PTK spreads out this debris but does not actually clean the interface. In our experience, PTK was not effective at removing interface debris compared to the manual cleaning technique. A cleaner interface will reduce corneal light scatter, which could reduce visual quality.

As a result of these modifications to our hyperopic LASIK routine, we have demonstrated that the induced myopia and the subsequent hyperopic shift are considerably lower than reported in other studies.6 This is the first hyperopic LASIK study performed in our center in which we observed an increase in BSCVA compared to preoperatively. Our study reports only 3-month results, which may not be considered adequate followup for hyperopic LASIK. However, we have noted through personal observation reduced regression and better refractive outcomes than other studies, even at this early juncture. We will continue to follow these patients long-term and note any significant changes. Another caveat of this study is that our preferred technique to treat hyperopia is based on age and the magnitude of hyperopia. This restricts hyperopic LASIK to patients who are aged <46 years and have ≤4.00 D of hyperopia. The ideal hyperopic LASIK candidate has ≤2.50 D of hyperopia. In patients aged 20 to 45 years, if the hyperopia is between 4.00 and 10.00 D, we prefer to use Staar Vision Intracorneal lens (STAAR Surgical Co, Monrovia, Calif). If the magnitude of the hyperopia is between 10.00 and 15.00 D, we prefer the use of clear lens exchange. All patients aged >45 years with >4.00 D of hyperopia undergo clear lens exchange. Patients aged >60 years undergo lensectomy with intraocular lens (IOL) implantation with alternatives such as accommodative or multifocal IOL.

REFERENCES

1. Cobo-Soriano R, Ll o vet F, Gonzalez-Lopez F, Domingo B, Gomez-Sanz F, Baviera J. Factors that influence outcomes of hyperopic laser in situ keratomileusis. J Cataract Refract Surg. 2002;28:1530-1538.

2. Qazi MA, Roberts CJ, Mahmoud AM, Pepose JS. Topographic and biomechanical differences between hyperopic and myopic laser in situ keratomileusis. J Cataract Refract Surg. 2005;31:48-60.

3. Anschutz T. Laser correction of hyperopia and presbyopia. Int Ophthalmol Clin. 1994;34:107-137.

4. Merchea M, Pieger S, Bains HS. Comparison of laser in situ keratomileusis outcomes with the Nidek EC -5 000 and M?dit?e Mel 70 excimer lasers. J Refract Surg. 2 002 ; 18 :S 34 3 -S 34 6.

5. Merchea M, Tokarewicz A. Comparison of laser in situ keratomileusis outcomes with the Nidek EC -5 000 and LSX LaserSight excimer lasers. J Refract Surg. 2001;17:S246-S249.

6. Jay cock PD, O'Brart DP, Rajan MS, Marshall J. 5 -year follow-up of LASIK for hyperopia. Ophthalmology. 2005;112:191-199.

7. Amoils SP. Photorefractive keratectomy using a scanning-slit laser, rotary epithelial brush, and chilled balanced salt solution. J Cataract Refract Surg. 2000;26:1596-1604.

TABLE

Values Corresponding to Figure 4 for Change in Mean Sphere, Mean Cylinder, and Mean Spherical Equivalent Refraction Over Time

Figure 5. Number of patients with distance BSCVA of 20/20 preoperatively and distance UCVA of 20/20 postoperatively.

10.3928/1081-597X-20050902-14

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