REVIEW URRENT C OPINION
Update on astigmatism management Ehsan Mozayan and Jimmy K. Lee
Purpose of review Astigmatism is a common refractive error that affects a significant portion of the population. This is a review of the most salient topics on assessing astigmatism as well as a discussion of the latest developments in surgical options and newest technologies to improve outcomes. Recent findings Laser corneal ablation continues to be highly effective for correcting low-to-moderate levels of astigmatism and may be the best option for the younger patient population. For eyes with astigmatism and cataracts, both peripheral corneal-relaxing incisions and cataract extraction with toric intraocular lenses have proven to be effective. Improved assessment of astigmatism, methods to select more accurate lens power, and new technologies to confirm proper axis alignment have all contributed to minimizing postoperative residual astigmatism. Summary Cataract surgery has evolved into a refractive procedure, in which not only the sphere but also cylinder errors can now be confidently corrected. Careful assessment and surgical planning of astigmatism should not be an option, but essential components of cataract surgery. Keywords astigmatism, peripheral corneal-relaxing incisions, topography, toric intraocular lens
INTRODUCTION Astigmatic refractive error is highly prevalent across all ethnicities. A recent survey of refractive errors in the European adult population of over 15 000 participants found that 32.3% had astigmatism [1]. A similar large-scale study of a multiethnic Asian population of over 10 000 adults found that 58.8% had astigmatism [2]. Numerous family and twin studies have alluded to a heritability of up to 60% [3,4], and recently a candidate gene has been identified [5 ]. This review will provide an update in assessing astigmatism, and review the current corneal and intraocular surgical options to address this refractive error. &
ASTIGMATISM ASSESSMENT Seminal to accurately measuring the magnitude and axis of astigmatism is an optimized ocular surface. Often, patients with regular or irregular astigmatism are soft or hard contact lens wearers and a period of contact lens holiday is recommended prior to assessment. A stable tear film and cornea devoid of epitheliopathy is critical for accurate measurements. Important especially for corneal laser vision correction is wavefront analysis, which measures higher order aberrations of the entire optical system. One www.co-ophthalmology.com
caveat to consider is that wavefront maps are dependent on pupil size and accommodation; therefore, in instances of corneal opacity or irregularity, data may not be adequately captured or the line of sight (pupil center) and the visual axis (corneal vertex) may not be aligned. Whereas manifest refraction and wavefront analysis takes into account the entire optical system, there are various modalities that measure corneal astigmatism: automated keratometry, manual keratometry, Placido-based corneal topography, Scheimpflug elevation mapping, and partial coherence interferometry (IOLMaster; Carl Zeiss Meditec, Jena, Germany). The advantages and disadvantages are that corneal curvature can be directly measured with Placido-disc technology, but must be calculated from the Scheimpflug data. Elevation mapping can be directly measured with Scheimpflug, but Montefiore Medical Center, New York, New York, USA Correspondence to Jimmy K. Lee, MD, Director of Refractive Surgery, Department of Ophthalmology and Visual Sciences, Assistant Professor, Albert Einstein College of Medicine, 3332 Rochambeau Avenue, 3rd Floor, Bronx, NY 10467, USA. Tel: +1 646 342 5546; e-mail: jimmylee @montefiore.org Curr Opin Ophthalmol 2014, 25:286–290 DOI:10.1097/ICU.0000000000000068 Volume 25 Number 4 July 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Update on astigmatism management Mozayan and Lee
KEY POINTS Corneal laser vision correction remains highly effective, especially for the treatment of moderate amounts of astigmatism (between 1 and 3 diopters). Peripheral corneal-relaxing incisions are becoming increasingly popular, with the latest improvements being femtosecond intrastromal incisions. New preoperative, intraoperative, and postoperative technologies are improving the outcomes of toric intraocular lenses.
must be derived with Placido-disc. Recently, the Galilei Dual Scheimpflug analyzer (Ziemer Ophthalmic Systems AG, Port, Switzerland), which combine the two, have shown repeatability of corneal power and wavefront aberration measurements [6]. Initial studies have reported similar measurement of astigmatism when comparing the aforementioned modalities. One report found agreement of mean corneal power, astigmatic power, and axis when comparing IOLMaster to two manual keratometers [7], and another found similar consistency when comparing manual keratometer, IOLMaster, Pentacam (Oculus, Wetzlar, Germany), and autokeratometer [8]. Although not a comparative study, one prospective multicenter study of toric intraocular lens (IOL) outcomes found that their 20/20 rates were higher with Lenstar LS-900 dual-zone automated keratometer (Haag-Streit AG, Koeniz, Switzerland) than the manufacturers package insert, in which manual keratometry was used for surgical planning [9].
CORNEAL LASER VISION CORRECTION If the patient is prepresbyopic or of precataractous age, has no ocular disease, and the wavefront aberrometry is consistent with manifest refraction and topography, corneal laser vision treatment is a viable option. Laser-assisted in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) are efficacious and popular for all types of refractive errors including corneal astigmatism. For high myopic [greater than 3 diopters (D)] astigmatism, LASIK and PRK were found to be comparably well tolerated, effective, and predictable with 39% of PRK and 54% of LASIK patients achieving less than 1 D, and 88% of PRK and 89% of LASIK eyes having less than 2 D of residual astigmatism [10]. Similar success with 65.3% within þ1.00 D was seen in those with high preoperative mixed astigmatism (over 3.0 D) [11]. In comparing PRK with mitomycin-C (MMC), without MMC, and trans-photorefractive
keratectomy (T-PRK) for the treatment of astigmatism with the Amaris 750s laser (Schwind eyetech-solutions, Kleinostheim, Germany), one group found similar effectiveness and safety between groups, with mean manifest refractive spherical equivalent (MRSE) of within þ0.50 D in 100, 100, and 93% of eyes, respectively [12]. Long-term findings from one study found that for all types of astigmatism (myopic, compound hyperopic, and mixed), UCVA was 20/25 or better in over 90% of eyes at 3 years [13]. Interestingly, recent findings warrant caution when treating low amounts of astigmatism. One study found that low myopic eyes with preoperative cylinder or less 0.50 D were significantly overcorrected with wavefront-optimized LASIK [14 ]. In another study in which preoperative astigmatism was minimal (less than 1.00 D), PRK and LASIK were found to induce substantial astigmatism, with surgically induced astigmatism positively correlated with greater levels of preoperative astigmatism [15]. &
PERIPHERAL CORNEAL-RELAXING INCISIONS Introduced over 25 years ago, peripheral cornealrelaxing incisions (PCRIs) continue to be effective and popular today [16]. Critical to the success of PCRIs are high-quality preoperative measurements, accurate surgical reference marks, incision of sufficient depth (90%), and fine-tuning of individual nomograms. To compensate for cyclotorsion, it is imperative to mark the patient’s horizontal (3 and 9 o’clock) meridians and 6 o’clock meridian if possible. The lowest cost method is to use the slit beam at the slit lamp oriented horizontally or a commercially available bubble level marker in the preoperative holding area. One group found that placing reference marks on the limbus, identifying the reference marks on the topographic image, and performing the relaxing incision based on the image were more accurate than basing the incisions without topographic reference [17]. Online nomograms (www.LRIcalculator.com) and smartphone apps have made the nomograms very convenient for the surgeon, with basic data required: patient’s age, keratometry, pachymetry, and surgeon-induced astigmatism. Several studies have compared PCRIs to toric IOLs for correcting astigmatism during cataract surgery. Although Hirnschall et al. [18 ] and Mingo-Botı´n et al. [19] found that the latter was more effective and predictable, Poll et al. [20] found both modalities to be comparable for mild-to-moderate levels; toric IOLs were more likely to achieve 20/40 UDVA in eyes with higher degrees of astigmatism, at least 2.26 D.
1040-8738 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
&
www.co-ophthalmology.com
287
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Refractive surgery
Another group found that combining toric IOLs with PCRIs in high astigmatism (>2.50 D) yielded an average reduction in cylindrical error from 3.90 D to 0.94 D and an average reduction in keratometric cylinder from 3.46 D to 1.80 D [21]. Femtosecond PCRIs are gaining popularity with precise axis placement and depth of incisions. The true advantage over manual incisional PCRIs, however, may be in equal efficacy without irritation or risk for infection [22,23] with intrastromal femtosecond PCRIs. One study of postkeratoplasty intrastromal PCRIs in eyes found a refractive cylinder reduction from 6.8 D to 3.7 D and topographic reduction from 9.5 D to 4.4 D [24]. Another interventional case series of 16 patients with naturally occurring or postcataract surgery astigmatism who were treated with femtosecond intrastromal PCRIs demonstrated a reduction in refractive and topographic reduction of cylinder from 1.41 D to 0.33 D and 1.50 D to 0.63 D, respectively [25].
TORIC INTRAOCULAR LENSES There are currently more than 10 monofocal IOLs and 4 multifocal IOLs in the market today [26 ]. In a randomized controlled trial, Holland et al. [27] reported less than 1.0 D postoperative residual refractive astigmatism in 88% of toric IOL eyes versus 48% in the monofocal group; 60% of the toric IOL group reported spectacle independence compared with 36% in the monofocal group. Although the success rates are impressive, there has been much debate as to how outcomes may be improved. At the heart are two concepts that did not gain much attention in the past: posterior corneal curvature and effective lens position (ELP). Koch et al. [28] found that ignoring posterior corneal astigmatism gave an incorrect estimation of total corneal astigmatism, with overestimation of withthe-rule (WTR) astigmatism and underestimation of against-the-rule (ATR) astigmatism. A nomogram has been proposed by the same group whereby for toric IOL calculations, 0.5 D would be subtracted in WTR astigmatism and 0.3 D would be added for ATR astigmatism [29 ]. The importance of posterior topography and tomography in toric IOL calculations has also been confirmed by using ray tracing software Okulix (Tedics, Dortmund, Germany) to predict residual refraction [30]. Another crucial assumption by toric IOL manufacturers that has raised much attention is that the ratio (1.46) of the IOL plane cylinder needed to neutralize the corneal plane cylinder is constant. In contrary, investigators have found that anterior chamber depth (ACD) and axial length can strongly influence the astigmatic power of toric IOLs [31 ]. &&
&&
&
288
www.co-ophthalmology.com
Savini et al. found that the ratio between toricity at the IOL plane and the corneal plane depend on the ACD; the highest ratio (1.86) was associated with the steepest K (48.0 D) and longest axial length (30.0 mm), whereas the lowest ratio (1.29) was associated with the flattest K (38.0 D) and shortest axial length (20.0 mm). When taking into consideration the ACD and spheroequivalent power of the IOL, Goggin et al. [32] also found that the manufacturer’s predicted fixed corneal plane cylinder power was substantially different from the calculated corneal cylinder power. To address this issue, Holladay [33] has proposed a table with different ratios for IOL cylinder to corneal cylinder for various ELPs and spheroequivalent powers. After selecting the appropriate power of the toric IOL, alignment of the IOL to the intended axis is the next challenge. Currently, most surgeons are manually marking reference 3, 6, and 9 o’clock meridians as mentioned in the PCRI section. However, new systems which use a preoperative noncontact reference unit to image the iris and limbal and scleral vessels, and overlay the image with the alignment axis onto the microscope during surgery have emerged to more accurately aid proper alignment. Currently available in the market are Surgery Guidance SG3000 (Sensomotoric Instruments GmbH, Teltow, Germany), Callisto (Carl Zeiss Meditec AG, Jena, Germany), and Verion (Alcon, Basel, Switzerland). Furthermore, intraoperative aberrometers, such as ORA (WaveTec, Also Viejo, California, USA) and HOLOS (Clarity Medical Systems, Inc. Pleasanton, California, USA) have been shown to be helpful in confirming the power of the toric IOLs in the aphakic status and allow finetuning of the axis alignment [34,35]. Rotational stability of the toric IOL is critical to optimal refractive outcomes, as there may be up to 3.3% loss of astigmatic correction for every degree of toric IOL misalignment. There are various methods of measuring or calculating postoperative IOL misalignment: slit lamp with a rotating slit, anterior segment optical coherence tomography [36], vector analysis [37], or using combined wavefront aberrometer/topographers such as iTrace (Tracey Technologies, Houston, Texas, USA), OPD-scan III (Nidek Inc., Fremont, California, USA), KR-1W (Topcon Medical Systems, Inc., Oakland, New Jersey, USA), Keratron Onda (Optikon 2000 SpA, Rome, Italy), or Discovery System (Innovative Visual Systems, Elmhurst, Illinois, USA). In the presence of significant residual refractive error, several options are available for the dissatisfied patient. If the refractive error is because of misalignment in the early postoperative phase and zonular stability is not in question, the toric Volume 25 Number 4 July 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Update on astigmatism management Mozayan and Lee
IOL may be repositioned [38]. In the latter scenario, the IOL may need to be exchanged with a capsular stabilizing ring or a three-piece monofocal IOL may need to be iris or scleral fixated. If repositioning or exchange of the IOL is not an option because of fibrosis of the capsular bag, the residual refractive error can be managed with excimer laser corneal ablation.
CONCLUSION In younger patients without cataracts, laser corneal surgery remains the mainstay of astigmatism correction. However, recent improvements in technologies that allow better assessment of astigmatism, more accurate IOL selection, and improved intraocular alignment are popularizing the use of toric IOLs as an effective option for concurrently addressing both astigmatism and cataracts. Conceptually, the new technologies are promising. However, future comparative studies will reveal whether they confer a true advantage. An encouraging trend is that these new technologies are merging into combination platforms, so that fewer scans from fewer modalities will be necessary. Acknowledgements Supported by an unrestricted grant from Research to Prevent Blindness to the Albert Einstein College of Medicine Department of Ophthalmology and Visual Sciences. Conflicts of interest The authors do not have any financial interests relevant to this article.
REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Pan CW, Zheng YF, Anuar AR, et al. Prevalence of refractive errors in a multiethnic Asian population: the Singapore Epidemiology of Eye Disease Study. Invest Ophthalmol Vis Sci 2013; 54:2590–2598. 2. Wolfram C, Ho¨hn R, Kottler U, et al. Prevalence of refractive errors in the European adult population: the Gutenberg Health Study (GHS). Br J Ophthalmol 2014. [Epub ahead of print] 3. Grjibovski AM, Magnus P, Midelfart A, Harris JR. Epidemiology and heritability of astigmatism in Norwegian twins: an analysis of self-reported data. Ophthalmic Epidemiol 2006; 13:245–252. 4. Hammond CJ, Snieder H, Gilbert CE, Spector TD. Genes and environment in refractive error: the twin eye study. Invest Ophthalmol Vis Sci 2001; 42:1232–1236. 5. Lopes MC, Hysi PG, Verhoeven VJ, et al. Identification of a candidate gene for & astigmatism. Invest Ophthalmol Vis Sci 2013; 54:1260–1267. This meta-analysis of seven Caucasian populations is the first to identify a candidate gene associated with astigmatism in the VAX2 gene region. 6. Wang L, Shirayama M, Koch DD. Repeatability of corneal power and wavefront aberration measurements with a dual-Scheimpflug Placido corneal topographer. J Cataract Refract Surg 2010; 36:425–430. 7. Bullimore MA, Buehren T, Bissmann W. Agreement between a partial coherence interferometer and 2 manual keratometers. J Cataract Refract Surg 2013; 39:1550–1560.
8. Chang M, Kang SY, Kim HM. Which keratometer is most reliable for correcting astigmatism with toric intraocular lenses? Korean J Ophthalmol 2012; 26:10–14. 9. Potvin R, Gundersen KG, Masket S, et al. Prospective multicenter study of toric IOL outcomes when dual zone automated keratometry is used for astigmatism planning. J Refract Surg 2013; 29:804–809. 10. Katz T, Wagenfeld L, Galambos P, et al. LASIK versus photorefractive keratectomy for high myopic (>3 diopter) astigmatism. J Refract Surg 2013; 29:824–831. 11. Alio JL, Pachkoria K, El Aswad A, Plaza-Puche AB. Laser-assisted in situ keratomileusis in high mixed astigmatism with optimized, fast-repetition and cyclotorsion control excimer laser. Am J Ophthalmol 2013; 155:829–836. 12. Baz O, Kara N, Bozkurt E, et al. Photorefractive keratectomy in the correction of astigmatism using Schwind Amaris 750 s laser. Int J Ophthalmol 2013; 6:356–361. 13. Roszkowska AM, De Grazia L, Meduri A, et al. Long-term results of excimer laser procedure to correct astigmatic refractive errors. Med Sci Monit 2013; 19:927–933. 14. Katz T, Frings A, Linke SJ, et al. Laser in situ keratomileusis for astigmatism & 0.75 diopter combined with low myopia: a retrospective data analysis. BMC Ophthalmol 2014; 14:1. This report cautions against full-laser ablation correction in cases of low myopia and compound astigmatism as it may result in overcorrection of cylinder. 15. Christiansen SM, Mifflin MD, Edmonds JN, et al. Astigmatism induced by conventional spherical ablation after PRK and LASIK in myopia with astigmatism < 1.00 D. Clin Ophthalmol 2012; 6:2109–2117. 16. Maguire LJ, Bourne WM. Corneal topography of transverse keratotomies for astigmatism after penetrating keratoplasty. Am J Ophthalmol 1989; 107:323– 330. 17. Miyata K, Miyai T, Minami K, et al. Limbal relaxing incisions using a reference point and corneal topography for intraoperative identification of the steepest meridian. J Refract Surg 2011; 27:339–344. 18. Hirnschall N, Gangwani V, Crnej A, et al. Correction of moderate corneal & astigmatism during cataract surgery: toric intraocular lens versus peripheral corneal relaxing incisions. J Cataract Refract Surg 2014; 40:354–361. This is the only prospective bilateral study that compared toric IOLs versus PCRIs. They found that the toric IOL Rayner-T (Rayner, East Sussex, UK) was more effective and predictable than PCRIs. 19. Mingo-Botı´n D, Mun˜oz-Negrete FJ, Won Kim HR, et al. Comparison of toric intraocular lenses and peripheral corneal relaxing incisions to treat astigmatism during cataract surgery. J Cataract Refract Surg 2010; 36:1700–1708. 20. Poll JT, Wang L, Koch DD, Weikert MP. Correction of astigmatism during cataract surgery: toric intraocular lens compared to peripheral corneal relaxing incisions. J Refract Surg 2011; 27:165–171. 21. Ouchi M, Kinoshita S. AcrySof IQ toric IOL implantation combined with limbal relaxing incision during cataract surgery for eyes with astigmatism >2.50 D. J Refract Surg 2011; 27:643–647. 22. Haripriya A, Syeda TS. A case of endophthalmitis associated with limbal relaxing incision. Indian J Ophthalmol 2012; 60:223–225. 23. Moon SW, Yeom DJ, Chung SH. Neurotrophic corneal ulcer development following cataract surgery with a limbal relaxing incision. Korean J Ophthalmol 2011; 25:210–213. 24. Wetterstrand O, Holopainen JM, Krootila K. Treatment of postoperative keratoplasty astigmatism using femtosecond laser-assisted intrastromal relaxing incisions. J Refract Surg 2013; 29:378–382. 25. Ru¨ckl T, Dexl AK, Bachernegg A, et al. Femtosecond laser-assisted intrastromal arcuate keratotomy to reduce corneal astigmatism. J Cataract Refract Surg 2013; 39:528–538. 26. Visser N, Bauer NJ, Nuijts RM. Toric intraocular lenses: historical overview, && patient selection, IOL calculation, surgical techniques, clinical outcomes, and complications. J Cataract Refract Surg 2013; 39:624–637. A comprehensive review on toric intraocular lenses with comparative analysis of currently available models. 27. Holland E, Lane S, Horn JD, et al. The AcrySof Toric intraocular lens in subjects with cataracts and corneal astigmatism: a randomized, subject-masked, parallelgroup, 1-year study. Ophthalmology 2010; 117:2104–2111. 28. Koch DD, Ali SF, Weikert MP, et al. Contribution of posterior corneal astigmatism to total corneal astigmatism. J Cataract Refract Surg 2012; 38:2080–2087. 29. Koch DD, Jenkins RB, Weikert MP, et al. Correcting astigmatism with toric && intraocular lenses: effect of posterior corneal astigmatism. J Cataract Refract Surg 2013; 39:1803–1809. The effect of posterior corneal astigmatism in addressing with toric intraocular lenses is analyzed, and a new nomogram to adjust for overestimation of with-therule astigmatism and underestimation of against-the-rule astigmatism is proposed. 30. Hoffmann PC, Wahl J, Hu¨tz WW, Preußner PR. A ray tracing approach to calculate toric intraocular lenses. J Refract Surg 2013; 29:402–408. 31. Savini G, Hoffer KJ, Carbonelli M, et al. Influence of axial length and corneal & power on the astigmatic power of toric intraocular lenses. J Cataract Refract Surg 2013; 39:1900–1903. Anterior chamber depth influenced the ratio (a standard number used by the lens manufacturer) between the cylinder power in the IOL plane and the corneal plane, and should be accounted for when selecting the power of the toric IOL in eyes with axial length and keratometry readings far from the average values.
1040-8738 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
www.co-ophthalmology.com
289
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Refractive surgery 32. Goggin M, Moore S, Esterman A. Outcome of toric intraocular lens implantation after adjusting for anterior chamber depth and intraocular lens sphere equivalent power effects. Arch Ophthalmol 2011; 129:998– 1003. 33. Holladay JT. Improving toric IOL outcomes. Ocular Surgery News. http:// www.osnsupersite.com/view.aspx?rid=83309. Published 25 May 2011 and 10 June 2011. 34. Ianchulev T, Hoffer KJ, Yoo SH, et al. Intraoperative refractive biometry for predicting intraocular lens power calculation after prior myopic refractive surgery. Ophthalmology 2014; 121:56–60.
290
www.co-ophthalmology.com
35. Krueger RR, Shea W, Zhou Y, et al. Intraoperative, real-time aberrometry during refractive cataract surgery with a sequentially shifting wavefront device. J Refract Surg 2013; 29:630–635. 36. Watanabe K, Negishi K, Torii H, et al. Simple and accurate alignment of toric intraocular lenses and evaluation of their rotation errors using anterior segment optical coherence tomography. Jpn J Ophthalmol 2012; 56:31–37. 37. Alpins NA, Goggin M. Practical astigmatism analysis for refractive outcomes in cataract and refractive surgery. Surv Ophthalmol 2004; 49:109–122. 38. Chang DF. Repositioning technique and rate for toric intraocular lenses. J Cataract Refract Surg 2009; 35:1315–1316.
Volume 25 Number 4 July 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Update on astigmatism management Ehsan Mozayan and Jimmy K. Lee
Purpose of review Astigmatism is a common refractive error that affects a significant portion of the population. This is a review of the most salient topics on assessing astigmatism as well as a discussion of the latest developments in surgical options and newest technologies to improve outcomes. Recent findings Laser corneal ablation continues to be highly effective for correcting low-to-moderate levels of astigmatism and may be the best option for the younger patient population. For eyes with astigmatism and cataracts, both peripheral corneal-relaxing incisions and cataract extraction with toric intraocular lenses have proven to be effective. Improved assessment of astigmatism, methods to select more accurate lens power, and new technologies to confirm proper axis alignment have all contributed to minimizing postoperative residual astigmatism. Summary Cataract surgery has evolved into a refractive procedure, in which not only the sphere but also cylinder errors can now be confidently corrected. Careful assessment and surgical planning of astigmatism should not be an option, but essential components of cataract surgery. Keywords astigmatism, peripheral corneal-relaxing incisions, topography, toric intraocular lens
INTRODUCTION Astigmatic refractive error is highly prevalent across all ethnicities. A recent survey of refractive errors in the European adult population of over 15 000 participants found that 32.3% had astigmatism [1]. A similar large-scale study of a multiethnic Asian population of over 10 000 adults found that 58.8% had astigmatism [2]. Numerous family and twin studies have alluded to a heritability of up to 60% [3,4], and recently a candidate gene has been identified [5 ]. This review will provide an update in assessing astigmatism, and review the current corneal and intraocular surgical options to address this refractive error. &
ASTIGMATISM ASSESSMENT Seminal to accurately measuring the magnitude and axis of astigmatism is an optimized ocular surface. Often, patients with regular or irregular astigmatism are soft or hard contact lens wearers and a period of contact lens holiday is recommended prior to assessment. A stable tear film and cornea devoid of epitheliopathy is critical for accurate measurements. Important especially for corneal laser vision correction is wavefront analysis, which measures higher order aberrations of the entire optical system. One www.co-ophthalmology.com
caveat to consider is that wavefront maps are dependent on pupil size and accommodation; therefore, in instances of corneal opacity or irregularity, data may not be adequately captured or the line of sight (pupil center) and the visual axis (corneal vertex) may not be aligned. Whereas manifest refraction and wavefront analysis takes into account the entire optical system, there are various modalities that measure corneal astigmatism: automated keratometry, manual keratometry, Placido-based corneal topography, Scheimpflug elevation mapping, and partial coherence interferometry (IOLMaster; Carl Zeiss Meditec, Jena, Germany). The advantages and disadvantages are that corneal curvature can be directly measured with Placido-disc technology, but must be calculated from the Scheimpflug data. Elevation mapping can be directly measured with Scheimpflug, but Montefiore Medical Center, New York, New York, USA Correspondence to Jimmy K. Lee, MD, Director of Refractive Surgery, Department of Ophthalmology and Visual Sciences, Assistant Professor, Albert Einstein College of Medicine, 3332 Rochambeau Avenue, 3rd Floor, Bronx, NY 10467, USA. Tel: +1 646 342 5546; e-mail: jimmylee @montefiore.org Curr Opin Ophthalmol 2014, 25:286–290 DOI:10.1097/ICU.0000000000000068 Volume 25 Number 4 July 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Update on astigmatism management Mozayan and Lee
KEY POINTS Corneal laser vision correction remains highly effective, especially for the treatment of moderate amounts of astigmatism (between 1 and 3 diopters). Peripheral corneal-relaxing incisions are becoming increasingly popular, with the latest improvements being femtosecond intrastromal incisions. New preoperative, intraoperative, and postoperative technologies are improving the outcomes of toric intraocular lenses.
must be derived with Placido-disc. Recently, the Galilei Dual Scheimpflug analyzer (Ziemer Ophthalmic Systems AG, Port, Switzerland), which combine the two, have shown repeatability of corneal power and wavefront aberration measurements [6]. Initial studies have reported similar measurement of astigmatism when comparing the aforementioned modalities. One report found agreement of mean corneal power, astigmatic power, and axis when comparing IOLMaster to two manual keratometers [7], and another found similar consistency when comparing manual keratometer, IOLMaster, Pentacam (Oculus, Wetzlar, Germany), and autokeratometer [8]. Although not a comparative study, one prospective multicenter study of toric intraocular lens (IOL) outcomes found that their 20/20 rates were higher with Lenstar LS-900 dual-zone automated keratometer (Haag-Streit AG, Koeniz, Switzerland) than the manufacturers package insert, in which manual keratometry was used for surgical planning [9].
CORNEAL LASER VISION CORRECTION If the patient is prepresbyopic or of precataractous age, has no ocular disease, and the wavefront aberrometry is consistent with manifest refraction and topography, corneal laser vision treatment is a viable option. Laser-assisted in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) are efficacious and popular for all types of refractive errors including corneal astigmatism. For high myopic [greater than 3 diopters (D)] astigmatism, LASIK and PRK were found to be comparably well tolerated, effective, and predictable with 39% of PRK and 54% of LASIK patients achieving less than 1 D, and 88% of PRK and 89% of LASIK eyes having less than 2 D of residual astigmatism [10]. Similar success with 65.3% within þ1.00 D was seen in those with high preoperative mixed astigmatism (over 3.0 D) [11]. In comparing PRK with mitomycin-C (MMC), without MMC, and trans-photorefractive
keratectomy (T-PRK) for the treatment of astigmatism with the Amaris 750s laser (Schwind eyetech-solutions, Kleinostheim, Germany), one group found similar effectiveness and safety between groups, with mean manifest refractive spherical equivalent (MRSE) of within þ0.50 D in 100, 100, and 93% of eyes, respectively [12]. Long-term findings from one study found that for all types of astigmatism (myopic, compound hyperopic, and mixed), UCVA was 20/25 or better in over 90% of eyes at 3 years [13]. Interestingly, recent findings warrant caution when treating low amounts of astigmatism. One study found that low myopic eyes with preoperative cylinder or less 0.50 D were significantly overcorrected with wavefront-optimized LASIK [14 ]. In another study in which preoperative astigmatism was minimal (less than 1.00 D), PRK and LASIK were found to induce substantial astigmatism, with surgically induced astigmatism positively correlated with greater levels of preoperative astigmatism [15]. &
PERIPHERAL CORNEAL-RELAXING INCISIONS Introduced over 25 years ago, peripheral cornealrelaxing incisions (PCRIs) continue to be effective and popular today [16]. Critical to the success of PCRIs are high-quality preoperative measurements, accurate surgical reference marks, incision of sufficient depth (90%), and fine-tuning of individual nomograms. To compensate for cyclotorsion, it is imperative to mark the patient’s horizontal (3 and 9 o’clock) meridians and 6 o’clock meridian if possible. The lowest cost method is to use the slit beam at the slit lamp oriented horizontally or a commercially available bubble level marker in the preoperative holding area. One group found that placing reference marks on the limbus, identifying the reference marks on the topographic image, and performing the relaxing incision based on the image were more accurate than basing the incisions without topographic reference [17]. Online nomograms (www.LRIcalculator.com) and smartphone apps have made the nomograms very convenient for the surgeon, with basic data required: patient’s age, keratometry, pachymetry, and surgeon-induced astigmatism. Several studies have compared PCRIs to toric IOLs for correcting astigmatism during cataract surgery. Although Hirnschall et al. [18 ] and Mingo-Botı´n et al. [19] found that the latter was more effective and predictable, Poll et al. [20] found both modalities to be comparable for mild-to-moderate levels; toric IOLs were more likely to achieve 20/40 UDVA in eyes with higher degrees of astigmatism, at least 2.26 D.
1040-8738 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
&
www.co-ophthalmology.com
287
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Refractive surgery
Another group found that combining toric IOLs with PCRIs in high astigmatism (>2.50 D) yielded an average reduction in cylindrical error from 3.90 D to 0.94 D and an average reduction in keratometric cylinder from 3.46 D to 1.80 D [21]. Femtosecond PCRIs are gaining popularity with precise axis placement and depth of incisions. The true advantage over manual incisional PCRIs, however, may be in equal efficacy without irritation or risk for infection [22,23] with intrastromal femtosecond PCRIs. One study of postkeratoplasty intrastromal PCRIs in eyes found a refractive cylinder reduction from 6.8 D to 3.7 D and topographic reduction from 9.5 D to 4.4 D [24]. Another interventional case series of 16 patients with naturally occurring or postcataract surgery astigmatism who were treated with femtosecond intrastromal PCRIs demonstrated a reduction in refractive and topographic reduction of cylinder from 1.41 D to 0.33 D and 1.50 D to 0.63 D, respectively [25].
TORIC INTRAOCULAR LENSES There are currently more than 10 monofocal IOLs and 4 multifocal IOLs in the market today [26 ]. In a randomized controlled trial, Holland et al. [27] reported less than 1.0 D postoperative residual refractive astigmatism in 88% of toric IOL eyes versus 48% in the monofocal group; 60% of the toric IOL group reported spectacle independence compared with 36% in the monofocal group. Although the success rates are impressive, there has been much debate as to how outcomes may be improved. At the heart are two concepts that did not gain much attention in the past: posterior corneal curvature and effective lens position (ELP). Koch et al. [28] found that ignoring posterior corneal astigmatism gave an incorrect estimation of total corneal astigmatism, with overestimation of withthe-rule (WTR) astigmatism and underestimation of against-the-rule (ATR) astigmatism. A nomogram has been proposed by the same group whereby for toric IOL calculations, 0.5 D would be subtracted in WTR astigmatism and 0.3 D would be added for ATR astigmatism [29 ]. The importance of posterior topography and tomography in toric IOL calculations has also been confirmed by using ray tracing software Okulix (Tedics, Dortmund, Germany) to predict residual refraction [30]. Another crucial assumption by toric IOL manufacturers that has raised much attention is that the ratio (1.46) of the IOL plane cylinder needed to neutralize the corneal plane cylinder is constant. In contrary, investigators have found that anterior chamber depth (ACD) and axial length can strongly influence the astigmatic power of toric IOLs [31 ]. &&
&&
&
288
www.co-ophthalmology.com
Savini et al. found that the ratio between toricity at the IOL plane and the corneal plane depend on the ACD; the highest ratio (1.86) was associated with the steepest K (48.0 D) and longest axial length (30.0 mm), whereas the lowest ratio (1.29) was associated with the flattest K (38.0 D) and shortest axial length (20.0 mm). When taking into consideration the ACD and spheroequivalent power of the IOL, Goggin et al. [32] also found that the manufacturer’s predicted fixed corneal plane cylinder power was substantially different from the calculated corneal cylinder power. To address this issue, Holladay [33] has proposed a table with different ratios for IOL cylinder to corneal cylinder for various ELPs and spheroequivalent powers. After selecting the appropriate power of the toric IOL, alignment of the IOL to the intended axis is the next challenge. Currently, most surgeons are manually marking reference 3, 6, and 9 o’clock meridians as mentioned in the PCRI section. However, new systems which use a preoperative noncontact reference unit to image the iris and limbal and scleral vessels, and overlay the image with the alignment axis onto the microscope during surgery have emerged to more accurately aid proper alignment. Currently available in the market are Surgery Guidance SG3000 (Sensomotoric Instruments GmbH, Teltow, Germany), Callisto (Carl Zeiss Meditec AG, Jena, Germany), and Verion (Alcon, Basel, Switzerland). Furthermore, intraoperative aberrometers, such as ORA (WaveTec, Also Viejo, California, USA) and HOLOS (Clarity Medical Systems, Inc. Pleasanton, California, USA) have been shown to be helpful in confirming the power of the toric IOLs in the aphakic status and allow finetuning of the axis alignment [34,35]. Rotational stability of the toric IOL is critical to optimal refractive outcomes, as there may be up to 3.3% loss of astigmatic correction for every degree of toric IOL misalignment. There are various methods of measuring or calculating postoperative IOL misalignment: slit lamp with a rotating slit, anterior segment optical coherence tomography [36], vector analysis [37], or using combined wavefront aberrometer/topographers such as iTrace (Tracey Technologies, Houston, Texas, USA), OPD-scan III (Nidek Inc., Fremont, California, USA), KR-1W (Topcon Medical Systems, Inc., Oakland, New Jersey, USA), Keratron Onda (Optikon 2000 SpA, Rome, Italy), or Discovery System (Innovative Visual Systems, Elmhurst, Illinois, USA). In the presence of significant residual refractive error, several options are available for the dissatisfied patient. If the refractive error is because of misalignment in the early postoperative phase and zonular stability is not in question, the toric Volume 25 Number 4 July 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Update on astigmatism management Mozayan and Lee
IOL may be repositioned [38]. In the latter scenario, the IOL may need to be exchanged with a capsular stabilizing ring or a three-piece monofocal IOL may need to be iris or scleral fixated. If repositioning or exchange of the IOL is not an option because of fibrosis of the capsular bag, the residual refractive error can be managed with excimer laser corneal ablation.
CONCLUSION In younger patients without cataracts, laser corneal surgery remains the mainstay of astigmatism correction. However, recent improvements in technologies that allow better assessment of astigmatism, more accurate IOL selection, and improved intraocular alignment are popularizing the use of toric IOLs as an effective option for concurrently addressing both astigmatism and cataracts. Conceptually, the new technologies are promising. However, future comparative studies will reveal whether they confer a true advantage. An encouraging trend is that these new technologies are merging into combination platforms, so that fewer scans from fewer modalities will be necessary. Acknowledgements Supported by an unrestricted grant from Research to Prevent Blindness to the Albert Einstein College of Medicine Department of Ophthalmology and Visual Sciences. Conflicts of interest The authors do not have any financial interests relevant to this article.
REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Pan CW, Zheng YF, Anuar AR, et al. Prevalence of refractive errors in a multiethnic Asian population: the Singapore Epidemiology of Eye Disease Study. Invest Ophthalmol Vis Sci 2013; 54:2590–2598. 2. Wolfram C, Ho¨hn R, Kottler U, et al. Prevalence of refractive errors in the European adult population: the Gutenberg Health Study (GHS). Br J Ophthalmol 2014. [Epub ahead of print] 3. Grjibovski AM, Magnus P, Midelfart A, Harris JR. Epidemiology and heritability of astigmatism in Norwegian twins: an analysis of self-reported data. Ophthalmic Epidemiol 2006; 13:245–252. 4. Hammond CJ, Snieder H, Gilbert CE, Spector TD. Genes and environment in refractive error: the twin eye study. Invest Ophthalmol Vis Sci 2001; 42:1232–1236. 5. Lopes MC, Hysi PG, Verhoeven VJ, et al. Identification of a candidate gene for & astigmatism. Invest Ophthalmol Vis Sci 2013; 54:1260–1267. This meta-analysis of seven Caucasian populations is the first to identify a candidate gene associated with astigmatism in the VAX2 gene region. 6. Wang L, Shirayama M, Koch DD. Repeatability of corneal power and wavefront aberration measurements with a dual-Scheimpflug Placido corneal topographer. J Cataract Refract Surg 2010; 36:425–430. 7. Bullimore MA, Buehren T, Bissmann W. Agreement between a partial coherence interferometer and 2 manual keratometers. J Cataract Refract Surg 2013; 39:1550–1560.
8. Chang M, Kang SY, Kim HM. Which keratometer is most reliable for correcting astigmatism with toric intraocular lenses? Korean J Ophthalmol 2012; 26:10–14. 9. Potvin R, Gundersen KG, Masket S, et al. Prospective multicenter study of toric IOL outcomes when dual zone automated keratometry is used for astigmatism planning. J Refract Surg 2013; 29:804–809. 10. Katz T, Wagenfeld L, Galambos P, et al. LASIK versus photorefractive keratectomy for high myopic (>3 diopter) astigmatism. J Refract Surg 2013; 29:824–831. 11. Alio JL, Pachkoria K, El Aswad A, Plaza-Puche AB. Laser-assisted in situ keratomileusis in high mixed astigmatism with optimized, fast-repetition and cyclotorsion control excimer laser. Am J Ophthalmol 2013; 155:829–836. 12. Baz O, Kara N, Bozkurt E, et al. Photorefractive keratectomy in the correction of astigmatism using Schwind Amaris 750 s laser. Int J Ophthalmol 2013; 6:356–361. 13. Roszkowska AM, De Grazia L, Meduri A, et al. Long-term results of excimer laser procedure to correct astigmatic refractive errors. Med Sci Monit 2013; 19:927–933. 14. Katz T, Frings A, Linke SJ, et al. Laser in situ keratomileusis for astigmatism & 0.75 diopter combined with low myopia: a retrospective data analysis. BMC Ophthalmol 2014; 14:1. This report cautions against full-laser ablation correction in cases of low myopia and compound astigmatism as it may result in overcorrection of cylinder. 15. Christiansen SM, Mifflin MD, Edmonds JN, et al. Astigmatism induced by conventional spherical ablation after PRK and LASIK in myopia with astigmatism < 1.00 D. Clin Ophthalmol 2012; 6:2109–2117. 16. Maguire LJ, Bourne WM. Corneal topography of transverse keratotomies for astigmatism after penetrating keratoplasty. Am J Ophthalmol 1989; 107:323– 330. 17. Miyata K, Miyai T, Minami K, et al. Limbal relaxing incisions using a reference point and corneal topography for intraoperative identification of the steepest meridian. J Refract Surg 2011; 27:339–344. 18. Hirnschall N, Gangwani V, Crnej A, et al. Correction of moderate corneal & astigmatism during cataract surgery: toric intraocular lens versus peripheral corneal relaxing incisions. J Cataract Refract Surg 2014; 40:354–361. This is the only prospective bilateral study that compared toric IOLs versus PCRIs. They found that the toric IOL Rayner-T (Rayner, East Sussex, UK) was more effective and predictable than PCRIs. 19. Mingo-Botı´n D, Mun˜oz-Negrete FJ, Won Kim HR, et al. Comparison of toric intraocular lenses and peripheral corneal relaxing incisions to treat astigmatism during cataract surgery. J Cataract Refract Surg 2010; 36:1700–1708. 20. Poll JT, Wang L, Koch DD, Weikert MP. Correction of astigmatism during cataract surgery: toric intraocular lens compared to peripheral corneal relaxing incisions. J Refract Surg 2011; 27:165–171. 21. Ouchi M, Kinoshita S. AcrySof IQ toric IOL implantation combined with limbal relaxing incision during cataract surgery for eyes with astigmatism >2.50 D. J Refract Surg 2011; 27:643–647. 22. Haripriya A, Syeda TS. A case of endophthalmitis associated with limbal relaxing incision. Indian J Ophthalmol 2012; 60:223–225. 23. Moon SW, Yeom DJ, Chung SH. Neurotrophic corneal ulcer development following cataract surgery with a limbal relaxing incision. Korean J Ophthalmol 2011; 25:210–213. 24. Wetterstrand O, Holopainen JM, Krootila K. Treatment of postoperative keratoplasty astigmatism using femtosecond laser-assisted intrastromal relaxing incisions. J Refract Surg 2013; 29:378–382. 25. Ru¨ckl T, Dexl AK, Bachernegg A, et al. Femtosecond laser-assisted intrastromal arcuate keratotomy to reduce corneal astigmatism. J Cataract Refract Surg 2013; 39:528–538. 26. Visser N, Bauer NJ, Nuijts RM. Toric intraocular lenses: historical overview, && patient selection, IOL calculation, surgical techniques, clinical outcomes, and complications. J Cataract Refract Surg 2013; 39:624–637. A comprehensive review on toric intraocular lenses with comparative analysis of currently available models. 27. Holland E, Lane S, Horn JD, et al. The AcrySof Toric intraocular lens in subjects with cataracts and corneal astigmatism: a randomized, subject-masked, parallelgroup, 1-year study. Ophthalmology 2010; 117:2104–2111. 28. Koch DD, Ali SF, Weikert MP, et al. Contribution of posterior corneal astigmatism to total corneal astigmatism. J Cataract Refract Surg 2012; 38:2080–2087. 29. Koch DD, Jenkins RB, Weikert MP, et al. Correcting astigmatism with toric && intraocular lenses: effect of posterior corneal astigmatism. J Cataract Refract Surg 2013; 39:1803–1809. The effect of posterior corneal astigmatism in addressing with toric intraocular lenses is analyzed, and a new nomogram to adjust for overestimation of with-therule astigmatism and underestimation of against-the-rule astigmatism is proposed. 30. Hoffmann PC, Wahl J, Hu¨tz WW, Preußner PR. A ray tracing approach to calculate toric intraocular lenses. J Refract Surg 2013; 29:402–408. 31. Savini G, Hoffer KJ, Carbonelli M, et al. Influence of axial length and corneal & power on the astigmatic power of toric intraocular lenses. J Cataract Refract Surg 2013; 39:1900–1903. Anterior chamber depth influenced the ratio (a standard number used by the lens manufacturer) between the cylinder power in the IOL plane and the corneal plane, and should be accounted for when selecting the power of the toric IOL in eyes with axial length and keratometry readings far from the average values.
1040-8738 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
www.co-ophthalmology.com
289
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Refractive surgery 32. Goggin M, Moore S, Esterman A. Outcome of toric intraocular lens implantation after adjusting for anterior chamber depth and intraocular lens sphere equivalent power effects. Arch Ophthalmol 2011; 129:998– 1003. 33. Holladay JT. Improving toric IOL outcomes. Ocular Surgery News. http:// www.osnsupersite.com/view.aspx?rid=83309. Published 25 May 2011 and 10 June 2011. 34. Ianchulev T, Hoffer KJ, Yoo SH, et al. Intraoperative refractive biometry for predicting intraocular lens power calculation after prior myopic refractive surgery. Ophthalmology 2014; 121:56–60.
290
www.co-ophthalmology.com
35. Krueger RR, Shea W, Zhou Y, et al. Intraoperative, real-time aberrometry during refractive cataract surgery with a sequentially shifting wavefront device. J Refract Surg 2013; 29:630–635. 36. Watanabe K, Negishi K, Torii H, et al. Simple and accurate alignment of toric intraocular lenses and evaluation of their rotation errors using anterior segment optical coherence tomography. Jpn J Ophthalmol 2012; 56:31–37. 37. Alpins NA, Goggin M. Practical astigmatism analysis for refractive outcomes in cataract and refractive surgery. Surv Ophthalmol 2004; 49:109–122. 38. Chang DF. Repositioning technique and rate for toric intraocular lenses. J Cataract Refract Surg 2009; 35:1315–1316.
Volume 25 Number 4 July 2014
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
