Journal of Refractive Surgery

Stability of Wavefront Aberrations During the Daytime After 6 Months of Overnight Orthokeratology Corneal Reshaping

Iane Stillitano, MD; Paulo Schor, MD; Cesar Lipener, MD; Ana Luisa Hofling-Lima, MD

Abstract

ABSTRACT

PURPOSE: To evaluate the stability of wavefront aberrations during the daytime after 6 months of overnight orthokeratology corneal reshaping.

METHODS: A prospective study of 26 eyes using the Ultravision BE lens design during 6 months of overnight wear. Uncorrected visual acuity (UCVA), cycloplegic refraction, and wavefront aberrometry were measured at 8 AM (within 1 hour after awakening and removing lenses), 1 PM (5 to 6 hours after lens removal), and 6 PM (10 to 12 hours after lens removal).

RESULTS: There was no significant difference in UCVA between 8 AM, 1 PM, and 6 PM (P= .383). Spherical power from wavefront aberrometry showed significant regression from 8 AM to 1 PM (P<.001) and stabilized near zero diopters. Total root-mean-square (RMS) increased and higher order aberration RMS and defocus (Z4) decreased between 8 AM and 1 PM (P<.001) but did not change for the rest of the day (P>.001). There was no statistically significant change in astigmatism (Z3 and Z5) (P=. 449) and coma (Z7 and Z8) (P=. 145) between 8 AM, 1 PM, and 6 PM. Spherical aberration (Z12) showed regression throughout the day (P<.001).

CONCLUSIONS: After 6 months of overnight orthokeratology wear, some optical aberrations showed regression during the day. Despite no significant change in UCVA during 10 to 12 hours, there was a significant increase in defocus (Z4) within the first 5 hours after removing the orthokeratology lens and a decrease in spherical aberration (Z12) throughout the day. [J Refract Surg. 2007;23:978-983.]

Abstract

ABSTRACT

PURPOSE: To evaluate the stability of wavefront aberrations during the daytime after 6 months of overnight orthokeratology corneal reshaping.

METHODS: A prospective study of 26 eyes using the Ultravision BE lens design during 6 months of overnight wear. Uncorrected visual acuity (UCVA), cycloplegic refraction, and wavefront aberrometry were measured at 8 AM (within 1 hour after awakening and removing lenses), 1 PM (5 to 6 hours after lens removal), and 6 PM (10 to 12 hours after lens removal).

RESULTS: There was no significant difference in UCVA between 8 AM, 1 PM, and 6 PM (P= .383). Spherical power from wavefront aberrometry showed significant regression from 8 AM to 1 PM (P<.001) and stabilized near zero diopters. Total root-mean-square (RMS) increased and higher order aberration RMS and defocus (Z4) decreased between 8 AM and 1 PM (P<.001) but did not change for the rest of the day (P>.001). There was no statistically significant change in astigmatism (Z3 and Z5) (P=. 449) and coma (Z7 and Z8) (P=. 145) between 8 AM, 1 PM, and 6 PM. Spherical aberration (Z12) showed regression throughout the day (P<.001).

CONCLUSIONS: After 6 months of overnight orthokeratology wear, some optical aberrations showed regression during the day. Despite no significant change in UCVA during 10 to 12 hours, there was a significant increase in defocus (Z4) within the first 5 hours after removing the orthokeratology lens and a decrease in spherical aberration (Z12) throughout the day. [J Refract Surg. 2007;23:978-983.]

The goal of overnight orthokeratology is to provide the patient with clear uncorrected visual acuity I (UCVA) during all waking hours. However, the induced corneal changes and refractive effect can regress during the day.1 Clinical studies1"5 of overnight orthokeratology have reported a similar pattern. Early in lens wear, a clinically significant regression of refractive effect can occur during the day, but once the target refraction is reached and the refractive error change stabilizes, daytime regression decreases significantly, averaging between 0.25 and 0.75 diopters (D). To allow this regression, orthokeratology practioners tend to aim for slight overcorrection of myopia (pseudohyperopia) on lens removal in the morning so that daytime regression does not compromise UCVA toward the end of the day.6

More recently, the study of optical aberrations has contributed to a better understanding of the effects of refractive procedures such as orthokeratology on visual quality.7,8 Factors that may affect a patient's vision include regression of myopia and fluctuation of optical aberrations throughout the day.8

Despite having observed a significant reduction in defocus (Z4) during a 1-week trial of overnight orthokeratology, Stillitano et al9 noted that higher order aberrations, particularly spherical aberration (Z12), increased in response to corneal remodeling. To date, the fluctuation of these ocular wavefront aberrations induced by orthokeratology has not been established. The current study analyzes the stability of lower order and higher order aberrations during the daytime after 6 months of overnight orthokeratology lens wear.

Table

TABLE 1Mean (Standard Deviation) Spherical Power From Wavefront Aberrometry and Uncorrected Visual Acuity 6 Months After Overnight Orthokeratology (N =26)

TABLE 1

Mean (Standard Deviation) Spherical Power From Wavefront Aberrometry and Uncorrected Visual Acuity 6 Months After Overnight Orthokeratology (N =26)

PATIENTS AND METHODS

PATIENTS

This was a prospective 6-month study of 26 eyes of 14 patients who were using the BE lens design (Ultravision Pty Ltd, Brisbane, Australia). These lenses were manufactured with Boston XO material, DK = 100 × 10^sup -11^ (cmp 2/s) (mL O2 / mL X mmHg) (ISO/Fatt) (Bausch & Lomb, Rochester, NY), and commercialized by Mediphacos Brazilian Enterprise. The study protocol was approved by the Federal University of São Paulo/Paulista School of Medicine, Medical Research Ethics Committee and followed the tenets of the Declaration of Helsinki. Written informed consent was obtained from all study participants after a thorough explanation of the risks and benefits of orthokeratology lens wear.

Inclusion criteria were myopia up to -4.50 diopters (D) with astigmatism of 1.50 D or less and best spectacle-corrected visual acuity (BSCVA) of 20/30 or better. Exclusion criteria included a history of ocular disease, rigid contact lens wear, or previous ocular surgery. The patients had not worn soft contact lenses for at least 4 weeks before enrolling in this study.

The BE contact lens was fitted in accordance with the guidelines provided by the manufacturer, which included the use of a proprietary computer program (BE Enterprises Studio, v. 1.1.3; Enterprise Ine, Vancouver, Canada) to determine the correct contact lens to order. Individuals who presented with a central bull's eye pattern on corneal topography after a 1-week trial were eligible for inclusion in this study and the retainer lenses were ordered.

All patients wore orthokeratology lenses while sleeping for at least 8 continuous hours per night and were requested to remove them immediately on waking. All patients underwent bilateral orthokeratology, with the exception of two anisometropic patients who wore a lens unilaterally. Study patients underwent testing three times a day at 8 AM (within 1 hour after awakening and removing lenses), 1 PM (5 to 6 hours after lens removal), and 6 PM (10 to 12 hours after lens removal) to measure UCVA, refraction, and ocular wavefront aberrations.

MEASUREMENTS

Visual acuity, cycloplegic refraction, and ocular wavefront measurements were used to determine the effectiveness and stability of the procedure.

Visual Acuity and Refraction. High-contrast UCVA was measured by using a projector chart and scored in logarithm of the minimum angle of resolution (logMAR) units. All measurements were obtained under low room illumination (10 cd/m2) in the same room and by the same investigator. Subjective cycloplegic refraction was performed after instilling two drops of 1% tropicamide, each drop separated by 10 minutes.

Aberrometry. Lower order and higher order aberrations were measured using the previously validated LADARWave Hartmann- Shack aberrometer (Alcon Laboratories Ine, Ft Worth, Tex).10 Measurements were acquired 30 minutes after instillation of one drop of 1% tropicamide at each visit. Patients were instructed to blink once and remain still, and five images were acquired after stabilization of the tear film as seen on the sensor spot pattern (generally within 2 seconds after blinking). Data from the five images were automatically averaged and subsequently analyzed for changes between 8 AM, 1 PM, and 6 PM. All wavefront data are reported for a 6.50-mm pupil diameter measured up to the 4th Zernike order and correspond to the Optical Society of America standards for reporting optical aberrations.11

DATA ANALYSIS

Data were analyzed for each patient's eye independently using Microsoft Excel 2000, version 9.0.2720 (Microsoft Corp, Redmond, Wash). Wavefront aberrations were compared at 8 AM, 1 PM, and 6 PM using the repeated measures analysis of variance. Wilcoxon test was used to determine pair-wise differences (eg, 8 AM × 1 PM). A P value of <.05 was considered statistically significant.

Table

TABLE 2Mean (Standard Deviation) Lower and Higher Order Aberrations (µm) Measured for a 6.50-mm Pupil Diameter to the 4th Zernike Order 6 Months After Overnight Orthokeratology (N =26)Figure 1. Mean values of root-mean-square (RMS) for all lower and higher order (total) aberrations for 26 eyes measured with a 6.50-mm pupil diameter to the 4th Zernike order measured at 8 am, 1 PM, and 6 PM at 6 months after overnight orthokeratology. Vertical bars denote 95% confidence intervals. Total RMS wavefront maps show the stability of corneal remodeling throughout the day.Figure 2. Mean values of root- mean-square (RMS) for higher order aberrations (HOA) for 26 eyes measured with a 6.50-mm pupil diameter to the 4th Zernike order measured at 8 am, 1 pm, and 6 PM at 6 months after overnight orthokeratology. Vertical bars denote 95% confidence intervals. Higher order aberrations wavefront maps show the stability of corneal remodeling throughout the day.

TABLE 2

Mean (Standard Deviation) Lower and Higher Order Aberrations (µm) Measured for a 6.50-mm Pupil Diameter to the 4th Zernike Order 6 Months After Overnight Orthokeratology (N =26)

Figure 1. Mean values of root-mean-square (RMS) for all lower and higher order (total) aberrations for 26 eyes measured with a 6.50-mm pupil diameter to the 4th Zernike order measured at 8 am, 1 PM, and 6 PM at 6 months after overnight orthokeratology. Vertical bars denote 95% confidence intervals. Total RMS wavefront maps show the stability of corneal remodeling throughout the day.

Figure 2. Mean values of root- mean-square (RMS) for higher order aberrations (HOA) for 26 eyes measured with a 6.50-mm pupil diameter to the 4th Zernike order measured at 8 am, 1 pm, and 6 PM at 6 months after overnight orthokeratology. Vertical bars denote 95% confidence intervals. Higher order aberrations wavefront maps show the stability of corneal remodeling throughout the day.

RESULTS

The mean spherical power measured from wavefront aberrometry at baseline was ?2. 10 ?0.80 D (range: -1.00 to -3.63 D). Table 1 shows the mean values of high-contrast UCVA and spherical power measured from wavefront for the morning, afternoon, and evening visits on the same day after 6 months of overnight orthokeratology lens wear. No significant difference in UCVA was found between 8 AM, 1 PM, and 6 PM (P=. 383). The mean value of spherical power from wavefront regressed between 8 AM and 1 PM and stabilized after 1 PM (P<.05).

The mean changes in total root-mean-square (RMS) and higher order aberration RMS for the three time periods are shown in Figures 1 and 2, respectively. A statistically significant increase was noted in total RMS between 8 AM and 1 PM (P<.05) and a statistically significant decrease in higher order aberration RMS between 8 AM and 1 PM (P<.05).

The mean values of lower order aberration and higher order aberrations measured at 8 AM, 1 PM, and 6 PM on the same day after 6 months of overnight orthokeratology lens wear are shown in Table 2. Defocus (Z4) increased 0.28 pm between 8 AM and 1 PM (P<.001). No statistically significant change was noted in astigmatism (Z3 and Z5) (P<.449) or coma (Z7 and Z8) (P<.145) throughout the day. Statistically significant decreases of spherical aberration (Z12) were observed throughout the day (P<.05).

Figure 3. Stability bar graph of root- meansquare (RMS) values for A) defocus, B) astigmatism, C) coma, and D) spherical aberration of 26 eyes measured at 8 am, 1 PM, and 6 PM after 6 months of overnight orthokeratology lens wear.

Figure 3. Stability bar graph of root- meansquare (RMS) values for A) defocus, B) astigmatism, C) coma, and D) spherical aberration of 26 eyes measured at 8 am, 1 PM, and 6 PM after 6 months of overnight orthokeratology lens wear.

Figure 3 plots the stability of defocus, astigmatism, coma, and spherical aberration of the 26 eyes at 8 AM, 1 PM, and 6 PM after 6 months of overnight orthokeratology lens wear.

DISCUSSION

Wavefront aberrometry has many applications in refractive procedures. The newest consists of analyzing the stability of orthokeratology corneal reshaping. Although Maldonado-Codina et al12 found the effect on myopia reduction was sustained for at least 5 hours after lens removal, which supports previous research,1,3 we observed that spherical power regressed -0.28±0.22 D during the first 5 hours. However, it has been sustained near zero diopters. This does not seem to affect the quantity of vision (visual acuity), but it might induce a loss in the quality of vision.

The rates of daytime regression tend to be greater for higher refractive correction and earlier in orthokeratology lens wear, but there are significant individual differences.5 This is expected to occur because greater changes are needed in greater ametropias and more corneal tissue is displaced and tends to return to its original state after orthokeratology.13

A study by Soni et al14 showed the full effect of overnight orthokeratology lens wear in patients with low myopia had stabilized within 1 week after initiating use of reverse-geometry lenses. Slow regression allows some patients to wear lenses only every second or third night while maintaining adequate daytime vision. Others require nightly lens wear to avoid reduced UCVA. The majority of our patients used their lenses every night. Three patients used their lenses for 5 nights consecutively followed by 2 nights off (weekend off), two patients used their lenses for 3 nights consecutively followed by 1 night off, and two patients used them every other night. This indicates that the effects of orthokeratology on refractive error and UCVA were temporary and reversible. Periodic retainer lens wear was necessary to maintain this refractive change.

We believe the knowledge of wavefront stability during orthokeratology is important for the understanding of subjective visual fluctuation and to improve futuregeneration reshaping strategies, including wavefrontguided orthokeratology lens design and clinical use. We found lower order aberrations appeared to fluctuate during the day. Defocus (Z4) increased between 8 AM and 1 PM (P<.001), but there was no significant change in astigmatism (Z3 and Z5) (P=. 449). We also observed that higher order aberrations appeared to fluctuate 12 hours after orthokeratology lens removal. Spherical aberration (Z12) decreased significantly throughout the day (P<.05), but coma (Z7 and Z8) did not show significant change (P=. 145).

Although coma remained stable, the most important initial step in orthokeratology reshaping is achieving the best fit of the lens, avoiding the induction of higher order aberrations. The highest induced coma was observed in patients 11, 12, and 23 (see Fig 3C); however, they remained stable throughout the day. The induction of small coma and its stability, as well as for other Zernike terms, is important to avoid damage on the visual system, such as double vision or ghosting.

Berntsen et al8 observed that, with the exception of spherical aberration, all calculated RMS values for a 5-mm pupil exhibited the same level of stability between morning and evening at 1 month after corneal refractive therapy. They found a significant increase of 0.025 ??? in spherical aberration from morning to evening after corneal refractive therapy. Unlike Berntsen et al,8 we observed that spherical aberration (Z12) decreased 0.114 pm from 8 AM to 6 PM after orthokeratology (P<.001), most probably reflecting a regression of the treatment. We believe the difference in studies is likely due to the different lenses used by Berntsen et al8 (Paragon lens) compared to our study (BE lens).

Despite the regression of defocus (Z4) and spherical aberration (Z12), we did not observe statistically significant changes in high-contrast UCVA between 8 AM and 6 PM. It is likely that the progressive decrease of spherical aberration (Z12) throughout the day could compensate for the increasing defocus (Z4) and minimize visual fluctuation. According to Applegate et al,15 the interaction of Zernike modes (eg, radial orders 2 and 4) that have the same angular frequency (0, ?2, or 2) can improve visual performance more than the individual modes.

The induced aberrations after 6 months of overnight orthokeratology lens wear appeared to regress during the day. Despite no significant change in UCVA during 10 to 12 hours, there was a significant increase in defocus (Z4) during the first 5 hours after removing the orthokeratology lens and a decrease in spherical aberration (Z12) throughout the day.

REFERENCES

1. Rah MJ, Jackson JM, Jones LA, Marsden HJ, Bailey MD, Barr JT. Overnight orthokeratology: preliminary results of the Lenses and Overnight Orthokeratology (LOOK) study. Optom Vis Sci. 2002;79:598-605.

2. Mountford J. Retention and regression of orthokeratology with time. Int Contact Lens Clin. 1998;25:59-64.

3. Nichols JJ, Marsich MM, Nguyen M, Barr JT, Bullimore MA. Overnight orthokeratology. Optom Vis Sci. 2000;77:252-259.

4. Sorbara L, Fonn D, Simpson T, Lu F, Kort R. Reduction of myopia from corneal refractive therapy. Optom Vis Sci. 2005;82:512-518.

5. Barr JT, Rah MJ, Meyers W, Legerton J. Recovery of refractive error after corneal refractive therapy. Eye Contact Lens. 2004;30:247-251.

6. Swarbrick HA. Orthokeratology review and update. Clin Exp Optom. 2006;89:124-143.

7. Joslin CE, Wu SM, McMahon TT, Shahidi M. Higher-order wavefront aberrations in corneal refractive therapy. Optom Vis Sci. 2003;80:805-811.

8. Berntsen DA, Barr JT, Mitchell GL. The effect of overnight contact lens corneal reshaping on higher-order aberrations and best-corrected visual acuity. Optom Vis Sci. 2005;82:490-497.

9. Stillitano I, Chalita MR, Schor P, Maidana E, Lui M, Lipener C, Hofling-Lima AL. Corneal changes and wavefront analysis on orthokeratology fitting test [published online ahead of press July 23, 2007]. Am J Ophthalmol. doi:10.1016/j.ajo.2007.05.030.

10. Miller JM, Anwaruddin R, Straub J, Schwieger ling J. Higher order aberrations in normal, dilated, intraocular lens, and laser in situ keratomileusis corneas. J Refract Surg. 2002;18:S579-S583.

11. Thibos LN, Applegate RA, Schwiegerling JT, Webb R, VSIA Standards Taskforce Members. Standards for reporting the optical aberrations of eyes. / Refract Surg. 2002;18:S652-S660.

12. Maldonado-Codina C, Efron S, Morgan P, Hough T, Efron N. Empirical versus trial set fitting systems for accelerated orthokeratology. Eye Contact Lens. 2005;31:137-147.

13. Haque S, Fonn D, Simpson T, Jones L. Corneal and epithelial thickness changes after 4 weeks of overnight corneal refractive therapy lens wear, measured with optical coherence tomography. Eye Contact Lens. 2004;30:189-193.

14. Soni PS, Nguyen TT, Bonanno JA. Overnight orthokeratology: refractive and corneal recovery after discontinuation of reversegeometry lenses. Eye Contact Lens. 2004;30:254-262.

15. Applegate RA, Marsack JD, Ramos R, Sarver EJ. Interaction between aberrations to improve or reduce visual performance. J Cataract Refract Surg. 2003;29:1487-1495.

TABLE 1

Mean (Standard Deviation) Spherical Power From Wavefront Aberrometry and Uncorrected Visual Acuity 6 Months After Overnight Orthokeratology (N =26)

TABLE 2

Mean (Standard Deviation) Lower and Higher Order Aberrations (µm) Measured for a 6.50-mm Pupil Diameter to the 4th Zernike Order 6 Months After Overnight Orthokeratology (N =26)

Figure 1. Mean values of root-mean-square (RMS) for all lower and higher order (total) aberrations for 26 eyes measured with a 6.50-mm pupil diameter to the 4th Zernike order measured at 8 am, 1 PM, and 6 PM at 6 months after overnight orthokeratology. Vertical bars denote 95% confidence intervals. Total RMS wavefront maps show the stability of corneal remodeling throughout the day.

Figure 2. Mean values of root- mean-square (RMS) for higher order aberrations (HOA) for 26 eyes measured with a 6.50-mm pupil diameter to the 4th Zernike order measured at 8 am, 1 pm, and 6 PM at 6 months after overnight orthokeratology. Vertical bars denote 95% confidence intervals. Higher order aberrations wavefront maps show the stability of corneal remodeling throughout the day.

10.3928/1081-597X-20071101-21

Sign up to receive

Journal E-contents