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Treatment of simple hyperopia: Comparison of laser in situ keratomileusis and laser thermal keratoplasty

Hill, John C. MD, FRCS*,a

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Journal of Cataract & Refractive Surgery: May 2003 - Volume 29 - Issue 5 - p 912-917
doi: 10.1016/S0886-3350(02)01990-9
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Abstract

Approximately 50% of eyes in the population fall in the hyperopic range.1 Patients in the +1.00 to +3.00 diopter (D) range represent 35% of the population—52.5 million potential patients in the United States (D.S. Durrie, MD, D.R. Sanders, MD, “LTK: Current and Future Applications for the Refractive Surgeon's Armamentarium,” EyeWorld 2000, October supplement, pages 1−12). Although asymptomatic in their early years, these patients ultimately require optical corrections for near and distance vision.

Several treatment modalities for simple hyperopia such as hexagonal keratotomy2 and automated lamellar keratoplasty3 have been suggested, but they have been abandoned because of unpredictability and instability. More recently, photorefractive keratectomy 4–9 and laser in situ keratomileusis (LASIK)10–12 have become treatment modalities for hyperopia and hyperopic astigmatism.

Another addition to the hyperopia treatment armamentarium is laser thermal keratoplasty (LTK), which offers the advantage of a noncontact technique that spares the central cornea and produces larger treatment optical zones.13,14 Recent trends indicate that LTK is becoming popular for treating low levels of hyperopia (+1.00 D), whereas LASIK remains the preferred choice for higher levels (+3.00 D).15 This paper presents the results of treating simple hyperopia of +3.0 D or less with LASIK using 2 excimer laser systems and compares them with the results in a similar group of eyes treated with LTK.

Patients and Methods

This retrospective study included consecutive eyes having treatment of simple hyperopia of +3.0 D or less. No eye with more than 0.5 D of astigmatism was included. The results are for the primary treatment only; although a number of retreatments (enhancements) were performed, the results are not included.

In the first LASIK group, 81 eyes were treated with the Nidek EC-5000 excimer laser using a 5.5 mm optical zone and a 7.5 mm transition zone. A nasally hinged corneal flap was made with the Automated Corneal Shaper® microkeratome (Bausch & Lomb Surgical). Postoperatively, a corticosteroid–antibiotic combination drop was instilled 4 times daily for 1 week. The clinical details are shown in Table 1.

Table 1
Table 1:
Clinical details of the 3 treatment groups

In the second LASIK group, 69 eyes were treated with the LaserSight LaserScan LSX® excimer laser using a 6.0 mm optical zone and an 8.5 mm transition zone. A superiorly hinged corneal flap was made with a Schwind Supratome® microkeratome. Postoperatively, a corticosteroid–antibiotic combination drop was instilled 4 times daily for 1 week. The clinical details are shown in Table 1.

In the LTK group, 84 eyes were treated by noncontact holmium:YAG LTK with the Sun 1000 Corneal Shaping System (Sunrise Technologies). Eight spots were placed at 6.0 mm and 7.0 mm concentric rings centered on the visual axis with the patient manually fixating on a target. Before treatment, a 3-minute drying period was allowed; energy levels were selected according to the manufacturer's nomogram. Postoperatively, diclofenac sodium and antibiotic drops were instilled 4 times daily for 1 week. The clinical details are shown in Table 1.

The first eyes were treated with the Nidek EC-5000 excimer laser and the next group, with LTK when the Sun System became available. When the LTK treatments were completed, the laser system had changed so the last eyes were treated with the LaserSight LSX excimer laser. Table 1 shows that the demographics of the 3 groups were similar except that there were more men than women in the LTK group. Posttreatment follow-up assessment were at 1, 3, 6, and 12 months; the information was stored and the statistical analysis performed by the Datagraph Med software program (outcomes analysis software version 2.8, Ingenieurbüro Pieger GmbH). Statistical analysis was performed using the Student t test, double sided for difference variance.

Results

Both LASIK groups showed undercorrection, but good stability was achieved after 1 month (Figure 1). There was some early refractive instability within the first few weeks, but this had resolved by 1 month. In the LTK group, there was typical overcorrection followed by a steady regression up to 12 months; the regression slowed but continued up to 18 months (Figure 1).

Figure 1.
Figure 1.:
(Hill) The mean achieved change in refraction over time (stability), standard deviation, and number of eyes in the 3 groups at 1, 3, 6, and 12 months.

Predictability in the 2 LASIK groups at 3 months is shown in Figure 2. There was undercorrection in both groups, but the achieved trend line in the LSX group is more linear, with increased undercorrection associated with larger attempted corrections. Because of the instability in the LTK group, predictability was difficult to tabulate; results at 3 and 12 months (Figure 3) were widely scattered.

Figure 2.
Figure 2.:
(Hill) Attempted versus achieved correction at 3 months (predictability). Left: LASIK with the Nidek EC-5000 laser (n = 59). Right: LASIK with the LaserSight LSX excimer laser (n = 51).
Figure 3.
Figure 3.:
(Hill) Attempted versus achieved correction in the LTK group (predictability). Left: At 3 months (n = 62). Right: At 12 months (n = 39).

Safety was good in all 3 groups (Figure 4). No eye lost more than 2 lines of best spectacle-corrected visual acuity (BSCVA). Loss of 2 lines occurred in 3% of eyes in the Nidek group, 1% of eyes in the LaserSight group, and no eye in the LTK group. The number of eyes that lost or gained 1 line of BSCVA was similar in the 3 groups.

Figure 4.
Figure 4.:
(Hill) The change in BSCVA (safety) at 3 months in the 3 groups.

The cumulative uncorrected visual acuity (UCVA) in the 3 groups at 3 months is shown in Figure 5. For comparison, the pretreatment BSCVA in all eyes in the groups is also shown.

Figure 5.
Figure 5.:
(Hill) The cumulative pretreatment BSCVA in the 3 groups combined and the posttreatment UCVA in each group at 3 months.

Surgically induced astigmatism (SIA) occurred in all 3 groups. Before treatment, all eyes had 0.5 D or less of astigmatism. The mean astigmatism was similar in the 3 groups (Table 2). At 3 months, the mean astigmatism in the 2 LASIK groups was similar: −0.47 ± 0.40 D (range 0 to −1.50 D) and −0.45 ± 0.40 D (range 0 to −1.25 D) in the Nidek group and the LSX group, respectively. The difference in SIA between the Nidek group and the LSX group was not statistically significant (P=.38). At 3 months, the mean astigmatism in the LTK group was higher: −0.81 ± 0.51 D (range 0 to −2.25 D) (Table 2). The difference in SIA between the LTK group and the 2 LASIK groups combined was not significant (P=.052). The difference in SIA between the LTK group and the LSX group was statistically significant (P=.029); the difference between the LTK group and the Nidek group was not (P=.18). Similar values of posttreatment astigmatism were obtained at 1, 6, and 12 months in the 3 groups.

Table 2
Table 2:
Preoperative and 3-month posttreatment astigmatism

The retreatment rates are shown in Table 3.

Table 3
Table 3:
Retreatment (enhancement) rates

Discussion

The definitive treatment for low hyperopia has not been established. Phakic intraocular lens implantation and clear lens extraction are reserved for higher degrees of hyperopia, and intracorneal implants remain investigational. Corneal refractive surgery remains the preferred method of treating hyperopia.15 In this study, LASIK and LTK were effective in treating hyperopia and demonstrated good safety results. Although there was early refractive instability during the first month in both LASIK groups, stability was achieved at the end of this period. There was significant scatter in the results as shown by the standard deviations in the stability graphs and the scatter of individual results in the predictability graphs. However, the stability at 1 month allows adjustment of personalized nomograms and performance of repeat treatments (enhancements).

The retreatment rates in both LASIK groups was similar, about 20%. These are higher than those for myopic treatments, which in our practice are about 6%. In the LTK group, there was a similar scatter of results but the overwhelming feature was the continued regression. In the early postoperative period, many patients find the initial overcorrection acceptable if it is not too excessive; this acceptability remains as regression to emmetropia and mild hyperopia occurs. As the hyperopia increases, patients become increasingly unhappy and request retreatment. The surgeon may find it difficult to decide on the timing of a repeat treatment knowing that regression is probably ongoing. In the LTK group, 38% of eyes required repeat treatments.

The cumulative UCVA at 3 months and the pretreatment BSCVA are shown in Figure 5. Before treatment, 81% of eyes had a BSCVA of 20/20. At 3 months, 41%, 50%, and 21% in the Nidek, LSX, and LTK groups, respectively, had this level of UCVA. Overall, these results are disappointing, but they represent primary treatments only and improved results were obtained after repeat treatments. One reason for the disappointing results was the SIA that occurred in all 3 groups. The SIA was greater in the LTK group and although it did not reach statistical significance when compared with that in the 2 LASIK groups combined, it did when compared to that in the LSX group alone.

The SIA poses a problem when repeat treatments are contemplated. Although it has been suggested that single placement of a thermal keratoplasty spot can steepen a flat axis, insufficient data exist to recommend this deviation from the standard nomogram. Consequently, LTK cannot be used to correct astigmatism and it is therefore necessary to offer LASIK treatment. In this study, 61% of LTK repeat treatments required LASIK.

The advantage of LTK is that it is a simple, relatively inexpensive treatment; however, if LASIK is required for repeat treatment, cost factors have to be considered, especially by practitioners who offer patients free repeat treatments. Because of the early stability and the relative ease of repeat treatments, I now prefer to treat simple hyperopia up to +3.5 D with LASIK and I have abandoned LTK.

References

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© 2003 by Lippincott Williams & Wilkins, Inc.