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Intraocular stability of an angle-supported phakic intraocular lens with changes in pupil diameter
ARTICLE
Intraocular stability of an angle-supported phakic intraocular lens with changes in pupil diameter Jorge L. Alio´, MD, PhD, David P. Pin˜ero, MSc, Esperanza Sala, OD, Francisco Amparo, MD
PURPOSE: To use anterior segment optical coherence tomography (AS-OCT) to evaluate the stability of a recently released angle-supported phakic intraocular lens (pIOL) in the anterior segment with changes in pupil diameter. SETTING: Keratoconus Unit, Vissum Corporation, Alicante, Spain. METHODS: In this observational cross-sectional study of consecutive eyes with moderate to high myopia, an AcrySof Cachet pIOL was implanted with the aim of minimizing the refractive error. An analysis of the position and stability of the pIOL before and after pharmacologic pupil dilation was performed 3 months postoperatively using the Visante AS-OCT system. A measurement protocol that included several anatomic parameters was developed and applied; the parameter values before and after dilation were compared. RESULTS: Twenty eyes of 20 patients ranging in age from 24 to 48 years old were evaluated. The anterior chamber depth increased significantly with pupil dilation (mean change 0.06 mm G 0.08 [SD]) (P<.01). A significant change was also observed in the distance between the center of the cornea at the endothelial plane and the anterior surface of the pIOL (mean change 0.03 G 0.05 mm) (P Z .01). The distances between the peripheral edges of the pIOL and the corneal endothelium and the distance between the crystalline lens and the pIOL did not change significantly (PR.14). CONCLUSION: The angle-supported pIOL showed excellent intraocular behavior after pupil dilation, with no shortening of the distance between the pIOL and corneal endothelium at the center or peripheral edges of the pIOL. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2010; 36:1517–1522 Q 2010 ASCRS and ESCRS
Over the past decades, studies of phakic intraocular lens (pIOL) implantation1–9 have shown the treatment’s efficacy in the correction of high refractive errors, providing an option to patients who are not suitable candidates for corneal refractive surgery. Phakic IOL implantation has advantages as a refractive procedure because of its potential reversibility, reasonable safety profile, and stability of refractive correction.1–9 Although all pIOLs have been improved to attain better biocompatibility with optimized optical properties,10 complications remain; these include pupil ovalization and corneal endothelial loss.11 Some complications are the result of inadequate selection of pIOL size,2,11 which means the pIOL cannot be customized to the individual eye. Phakic IOLs can be classified into the following 3 categories based on their position in the eye or their mechanism of fixation: anterior chamber angleQ 2010 ASCRS and ESCRS Published by Elsevier Inc.
supported, anterior chamber iris-fixated, and posterior chamber. Several studies of the results of the 3 pIOL models have been published.1–11 A recently released model, the AcrySof Cachet angle-supported pIOL (Alcon, Inc.), is of foldable hydrophobic acrylic, which gives the haptics significant foldability. This would theoretically reduce damage to angle structures and decrease the risk for pupil ovalization when the pIOL is placed in the anterior chamber. Excellent refractive correction and predictability with acceptable safety during the first year of follow-up have been reported.1 In addition, the stability of the pIOL has been corroborated, with minimum or insignificant rotation in a large percentage of cases.1 However, to our knowledge, the stability of this pIOL with changes in pupil diameter has not been evaluated. This is relevant given the characteristics of any anterior chamber angle-supported pIOL and the 0886-3350/$dsee front matter doi:10.1016/j.jcrs.2010.02.028
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position of this pIOL model in the anterior chamber. Indeed, pupil movement has been related to positional changes of other pIOLs in the anterior segment of the eye.12–15 These positional changes could modify the relative position of the pIOL in respect to the corneal endothelium and iridocorneal angle and have the potential to damage anterior chamber structures. New advanced imaging technology, such as veryhigh-frequency ultrasonography16 and optical coherence tomography (OCT),13 allow visualization and characterization of changes in the anterior segment in eyes with IOLs. The aim of the current study was to use anterior segment OCT (AS-OCT) to evaluate the stability of this angle-supported pIOL in the anterior segment with changes in pupil diameter. PATIENTS AND METHODS This observational cross-sectional study included consecutive eyes with moderate to high myopia that had implantation of an AcrySof Cachet pIOL with the aim of minimizing the refractive error. Before surgery, patients were extensively informed about the surgery, its risks, and its benefits, and all signed an informed consent form in accordance with the Declaration of Helsinki. Ethical committee approval was obtained for the study. The inclusion criteria for pIOL implantation and thus for study inclusion were a stable refractive error during the previous 2 years, an endothelial cell count of 2000 cells/mm2 or higher, an anterior chamber depth (ACD) (distance between endothelium and anterior surface of crystalline lens) of 2.8 mm or greater, and no previous or current ocular pathology or cataract.
Surgical Technique The same surgeon (J.L.A.) performed all operations at Vissum Corporation, Instituto Oftalmolo´gico de Alicante, Spain. The pIOL was implanted using a previously described technique.1 The pIOL size was chosen according to preoperative AS-OCT measurement of the horizontal angle-to-angle distance using a previously described measurement procedure (ie, distance between vertex of both iridocorneal angles at the horizontal meridian).17 Postoperative treatment Submitted: January 20, 2010. Final revision submitted: February 10, 2010. Accepted: February 17, 2010. From the Keratoconus Unit (Alio´, Pin˜ero, Sala, Amparo), Vissum Corporation, the Division of Ophthalmology (Alio´), Universidad Miguel Herna´ndez, and the Departamento de O´ptica (Pin˜ero), Farmacologı´a y Anatomı´a, Universidad de Alicante, Alicante, Spain. Supported in part by a grant from the Spanish Ministry of Health, Instituto Carlos III, Red Tema´tica de Investigacio´n Cooperativa en Salud Patologı´a Ocular del Envejecimiento, Calidad Visual y Calidad de Vida, Subproyecto de Calidad Visual (RD07/0062). Corresponding author: Jorge L. Alio´, MD, PhD, Avenida de Denia s/n, Edificio Vissum, 03016 Alicante, Spain. E-mail: [email protected].
Figure 1. Anterior segment OCT analysis of pIOL position under pupil dilation in 1 case shows the following measurements: horizontal pupil size, 6.71 mm; central cornea–pIOL distance, 2.10 mm; temporal cornea–pIOL distance, 1.45 mm; nasal cornea–pIOL distance, 1.43 mm; distance from the vertex of the anterior surface of the crystalline lens and the posterior surface of the pIOL, 1.10 mm; temporal iridocorneal angle, 41.1 degrees; nasal iridocorneal angle, 39.9 degrees.
consisted of dexamethasone 0.1% 3 times a day for 2 weeks and ciprofloxacin 0.3% 3 times a day for 1 week.
Postoperative Examinations The position and stability of the pIOL were evaluated with the Visante AS-OCT system (Carl Zeiss Meditec) 3 months after surgery. The same experienced examiner (E.S.) performed all measurements using the digital tools of the AS-OCT system software. The following parameters were evaluated before pupil dilation (basal conditions, photopic stimulation of the presented optotype) and after pupil dilation with 1 drop of phenylephrine 10% and 1 drop of tropicamide 1%: 1. Horizontal pupil size, which was measured as the distance between temporal and nasal pupil margins. 2. Central ACD, which was measured as the distance from the corneal endothelium to the anterior surface of the crystalline lens. 3. Horizontal angle-to-angle distance, which was measured as the distance between the vertex of the temporal and nasal iridocorneal angles. 4. Distance from the anterior surface of the pIOL and the corneal endothelium at different points (center, temporal, and nasal edges of the anterior surface of the pIOL). These distances were measured over a line perpendicular to the curvature of the posterior cornea (central cornea–pIOL distance, temporal cornea–pIOL distance, nasal cornea– pIOL distance). 5. Distance from the vertex of the anterior surface of the crystalline lens and the posterior surface of the pIOL (crystalline lens–pIOL distance) over a line perpendicular to the surface of the pIOL. 6. Temporal and nasal iridocorneal angles. Figure 1 shows an AS-OCT image of measurements of these parameters. All measurements under pupil dilation were performed 20 minutes after drop instillation.
Statistical Analysis Statistical analysis was performed using SPSS software for Windows (version 15.0, SPSS, Inc.). Normality of the data
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Table 1. Comparison of changes before and after pharmacologic pupil dilation.
Parameter
Before Pupil Dilation
Horizontal pupil size (mm) Mean G SD 4.36 C 0.86 Range 2.47 to 6.20 Central ACD (mm) Mean G SD 3.21 C 0.27 Range 2.80 to 3.67 Horizontal ATA distance (mm) Mean G SD 12.08 C 0.44 Range 11.13 to 13.01 Central cornea–pIOL distance (mm) Mean G SD 2.03 C 0.25 Range 1.55 to 2.47 Temporal cornea–pIOL distance (mm) Mean G SD 1.44 C 0.22 Range 1.07 to 1.80 Nasal cornea–pIOL distance (mm) Mean G SD 1.44 C 0.22 Range 0.96 to 1.76 Crystalline lens–pIOL distance (mm) Mean G SD 0.94 C 0.19 Range 0.45 to 1.41 Temporal iridocorneal angle (degrees) Mean G SD 38.24 C 8.76 Range 26.10 to 60.50 Nasal iridocorneal angle (degrees) Mean G SD 37.61 C 7.68 Range 26.30 to 54.00
After Pupil Dilation
P Value !.01
6.57 C 0.75 4.50 to 7.65 !.01 3.27 C 0.23 2.92 to 3.60 .14 12.18 C 0.46 11.18 to 12.77 .01 2.07 C 0.26 1.61 to 2.53 .16 1.46 C 0.19 1.16 to 1.75 .30 1.46 C 0.23 1.00 to 1.80 .43 0.95 C 0.21 0.35 to 1.43 !.01 45.98 C 7.92 32.70 to 64.58 !.01 43.43 C 7.39 30.40 to 58.40
ACD Z anterior chamber depth; ATA Z angle-to-angle; pIOL Z phakic intraocular lens
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distance (0.09 G 0.27 mm) with dilation was not statistically significant (P Z .14). Regarding the position of the pIOL in the anterior chamber, a significant change was only observed in the distance between the center of the cornea at the endothelial plane and the anterior surface of the pIOL (mean change 0.03 G 0.05 mm) (P Z .01). The other parameters characterizing the pIOL position did not change significantly with pupil dilation (PR.14) (Table 1). Evaluation of the relationship between the changes in anatomic parameters and the baseline values showed a statistically significant correlation between pupil change and pupil diameter before dilation (r Z 0.650, P!.01). The change in ACD with pharmacologic pupil dilation was significantly correlated with the baseline values of the following parameters characterizing the position of the pIOL: central cornea–pIOL distance (r Z 0.549, P Z .01), temporal cornea–pIOL distance (r Z 0.610, P!.01), and nasal cornea–pIOL distance (r Z 0.534, P Z .02) (Figure 2). Other statistically significant correlations were between the change in ACD and the baseline ACD (r Z 0.515, P Z .02) and between the change in temporal cornea–pIOL distance and the baseline temporal cornea–pIOL distance (r Z 0.527, P Z .02). Figure 3 shows an example of the positional changes of the pIOL after pharmacologic dilation in 1 case. The images show an increase in the distance between the pIOL and the corneal endothelium at the center as well as the opening of the iridocorneal angles. DISCUSSION
samples was first checked by the Kolmogorov-Smirnov test. The use of parametric statistics was always possible because all data samples followed a normal distribution; therefore, the Student t test for paired data was used for all parameter comparisons before and after pupil dilation with the same level of significance (P!.05). Pearson correlation coefficients were used to assess the correlation between variables. The mean values G SD are given.
RESULTS The study evaluated 20 consecutive eyes (13 right, 7 left) of 20 patients. The patients ranged in age from 24 to 48 years. Table 1 shows the changes in anatomic parameters after pupil dilation. As expected, the pupil size increased significantly (mean change 2.21 G 0.63 mm) and the temporal and nasal iridocorneal angles became significantly wider (mean change 7.75 G 6.54 degrees and 5.82 G 5.89 degrees, respectively) after pharmacologic dilation (all P!.01). The ACD also increased significantly (mean change 0.06 G 0.08 mm) (P!.01). The mean change in the angle-to-angle
Phakic IOLs have been shown to be useful in the correction of moderate to high myopia.1–9 Implantation of pIOLs leads to better postoperative quality of vision than keratorefractive excimer laser surgery in the same myopic eyes.18,19 However, questions remain about the potential long-term risks to anterior segment structures. Phakic IOLs should be well positioned with adequate stability so they do not damage the corneal endothelium and anterior lens capsule.10,11,20 Therefore, stability of the pIOL in relationship to the intraocular structures is crucial to good performance over time because a lack of stability is directly related to complications. Baumeister et al.21 found no significant movement of 2 anterior chamber IOLs (Artisan, Ophtec; NuVita, Bausch & Lomb) in an anteroposterior direction at 3 months and 12 months, whereas a posterior chamber pIOL (Implantable Collamer Lens, Staar Surgical Co.) showed significant movement toward the crystalline lens. A change in pIOL position can lead to complications, such as endothelial
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Figure 2. Scattergrams of the relationship between the change in the ACD with pharmacologic dilation and baseline values of parameters characterizing the position of the pIOL in the eye. A: Distance from the center of the anterior surface of the pIOL to the corneal endothelium (CCLD). B: Distance from the temporal edge of the anterior surface of the pIOL to the corneal endothelium (TCLD). C: Distance from the nasal edge of the anterior surface of the pIOL to the corneal endothelium (NCLD). The adjusting line to the data obtained by means of the least-squares fit is shown in all the graphs and was calculated as follows: Change in ACD (mm) Z 0.18 CCLD (mm) C 0.13 (r2 Z 0.301); change in ACD (mm) Z 0.24 TCLD (mm) C 0.40 (r2 Z 0.372); and change in ACD (mm) Z 0.21 NCLD (mm) C 0.36 (r2 Z 0.285).
damage; a reason for the change is the dynamics of the pIOL as the pupil size changes. Several studies12–15 report that some pIOL models change position with pupil movement. For example, Cruysberg et al.12 found a decrease in the distance between an irisfixated pIOL and the crystalline lens, suggesting posterior displacement of the pIOL with dark-induced pupil dilation, as well as an increase in the distance between the pIOL and the corneal endothelium. In a study by Petternel et al.,15 copolymer posterior chamber pIOLs moved backward after pilocarpine instillation while the distance between the pIOL and crystalline lens decreased under natural photopic conditions. However, to our knowledge, changes in the position of angle-supported pIOLs with pupil size modifications have not been reported. Thus, we used AS-OCT to evaluate the stability of a recently released angle-supported pIOL in the anterior segment after pharmacologic pupil dilation. The AS-OCT system we used to characterize the anterior segment and the position of the pIOL in the eye allows visualization and evaluation of all anterior
segment structures in front of the iris22 but cannot detect structures behind pigmented tissue such as the iris23 (less useful for posterior chamber evaluation). Anterior segment OCT has a resolution similar to that of ultrasound devices (approximately 20 mm) and excellent repeatability.23,24 The applications described for AS-OCT include analysis of the position of pIOLs.13,25,26 Considering the advantages of ASOCT imaging technology and based on the objectives of our study and the type of pIOL we analyzed (angle-supported anterior chamber), we believed the technology would provide a valid tool for our purposes. We developed a protocol to evaluate the position of the pIOL with the AS-OCT system. The protocol included the following parameters: distance from the anterior surface of the pIOL to the corneal endothelium at different points, distance from the vertex of the anterior surface of the crystalline lens to the posterior surface of the pIOL, and anterior segment feature (ACD, angle-to-angle distance, and iridocorneal angles). Regarding the anatomic changes in the anterior segment with pupil dilation, we found a small but
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Figure 3. Example of the positional changes of the angle-supported pIOL after pharmacologic dilation in 1 specific case. Top: Before pupil dilation. Bottom: After pupil dilation. Note the increase in the distance between the pIOL and the corneal endothelium at the center and the opening of the iridocorneal angles.
statistically significant increase in ACD. This finding is consistent with anterior segment changes related to pupil size modifications reported by other authors.27,28 In a study by Baikoff et al.,27 with 1.00 diopter of accommodation and the corresponding miosis (mean pupil diameter decrease 0.15 mm), the anterior pole moved forward by a mean of 30 mm, with a decrease (approximately 0.3 mm) in the radius of curvature of the anterior surface of the crystalline lens. Therefore, it seems as though changes in ACD are related to changes in the shape of the anterior surface of the crystalline lens. On the other hand, iridocorneal angles (temporal and nasal) increased significantly with pupil dilation. This finding seems logical: As the anterior surface of the crystalline lens became flatter, the iris moved backward, opening the angle. This is consistent with outcomes in a previous study28 in which wide chamber angles had a tendency to become narrower and narrow angles to become wider after instillation of pilocarpine. (We included only patients with wide iridocorneal angles.) A possible reason for this tendency is the change in iris volume that occurs with pupil dilation.29 Furthermore, we found no significant changes in the horizontal diameter of the anterior chamber (angle-to-angle distance), and our mean
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values before and after pupil dilation are consistent with those reported in the literature.17,30 Regarding the position of the pIOL, we found no significant changes in the distances between the edges of the anterior surface of the pIOL and the corneal endothelium, which implies that with pupil dilation, the relative position of the periphery of the pIOL and the corneal endothelium is stable. Phakic IOLs to correct high myopia are thicker in the periphery than in the center. Therefore, it is crucial to maintain the peripheral edges of the pIOL as far as possible from the corneal endothelium in all physiologic ocular conditions, such as pupil changes or accommodation. The distance between the center of the pIOL and the corneal endothelium increased significantly, although the change was of small magnitude, as with the ACD. Therefore, it seems the 2 types of changes occur simultaneously; that is, a change in the position of the central portion of the pIOL due to a change in the pIOL curvature in this area. In addition, the anterior crystalline lens curvature also changed as a result of the cycloplegic effect; therefore, the distance between the crystalline lens and the back surface of the pIOL did not change significantly with pupil dilation, as expected. The pIOL we used is flexible; therefore, its curvature is probably modified slightly with backward movement of the iris and flattening of the anterior surface of the crystalline lens. In conclusion, the AcrySof Cachet pIOL showed excellent intraocular behavior after pupil dilation, with no shortening of the distance between the pIOL and the corneal endothelium at the center or peripheral edges of the pIOL. Although there was a slight tendency for the central pIOL to move backward after pharmacologic dilation, the distance between the pIOL edges and the endothelium remained constant. Therefore, sufficient space was maintained between the pIOL and the anterior segment structures after pupil dilation, preventing the possibility of unwanted pIOL contact with ocular structures. Future studies should evaluate the potential refractive and optical effects of modification of the central area of the pIOL. REFERENCES 1. Kohnen T, Knorz MC, Cochener B, Gerl RH, Arne´ J-L, Colin J, Alio´ JL, Bellucci R, Marinho A. AcrySof phakic angle-supported intraocular lens for the correction of moderate-to-high myopia: one-year results of a multicenter European study. Ophthalmology 2009; 116:1314–1321 2. Alio´ JL, Pin˜ero D, Bernabeu G, Galal A, Vargas JM, Ismail MM. The Kelman Duet phakic intraocular lens: 1-year results. J Refract Surg 2007; 23:868–879 3. Benedetti S, Casamenti V, Marcaccio L, Brogioni C, Assetto V. Correction of myopia of 7 to 24 diopters with the Artisan phakic intraocular lens: two-year follow-up. J Refract Surg 2005; 21:116–126
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4. Leccisotti A, Fields SV. Clinical results of ZSAL-4 angle-supported phakic intraocular lenses in 190 myopic eyes. J Cataract Refract Surg 2005; 31:318–323 5. Alio´ JL, Mulet ME, Shalaby AMM. Artisan phakic iris claw intraocular lens for high primary and secondary hyperopia. J Refract Surg 2002; 18:697–707 6. Allemann N, Chamon W, Tanaka HM, Mori ES, Campos M, Schor P, Baikoff G. Myopic angle-supported intraocular lenses; two-year follow-up. Ophthalmology 2000; 107:1549–1554 7. Pe´rez-Santonja JJ, Alio´ JL, Jime´nez-Alfaro I, Zato MA. Surgical correction of severe myopia with an angle-supported phakic intraocular lens. J Cataract Refract Surg 2000; 26:1288–1302 8. Alio´ JL, de la Hoz F, Pe´rez-Santonja JJ, Ruiz-Moreno JM, Quesada JA. Phakic anterior chamber lenses for the correction of myopia; a 7-year cumulative analysis of complications in 263 cases. Ophthalmology 1999; 106:458–466 9. Baikoff G, Arne JL, Bokobza Y, Colin J, George JL, Lagoutte F, Lesure P, Montard M, Saragoussi JJ, Secheyron P. Angle-fixated anterior chamber phakic intraocular lens for myopia of 7 to 19 diopters. J Refract Surg 1998; 14:282–293 10. Alio JL. Advances in phakic intraocular lenses: indications, efficacy, safety, and new designs. Curr Opin Ophthalmol 2004; 15: 350–357 11. Chang DH, Davis EA. Phakic intraocular lenses. Curr Opin Ophthalmol 2006; 17:99–104 12. Cruysberg LPJ, Doors M, Berendschot TTJM, De Brabander J, Webers CAB, Nuijts RMMA. Iris-fixated anterior chamber phakic intraocular lens for myopia moves posteriorly with mydriasis. J Refract Surg 2009; 25:394–396 13. Koivula A, Kugelberg M. Optical coherence tomography of the anterior segment in eyes with phakic refractive lenses. Ophthalmology 2007; 114:2031–2037 14. Maldonado MJ, Garcı´a-Feijoo´ J, Benı´tez Del Castillo JM, Teutsch P. Cataractous changes due to posterior chamber flattening with a posterior chamber phakic intraocular lens secondary to the administration of pilocarpine. Ophthalmology 2006; 113:1283–1288 15. Petternel V, Ko¨ppl C-M, Dejaco-Ruhswurm I, Findl O, Skorpik C, Drexler W. Effect of accommodation and pupil size on the movement of a posterior chamber lens in the phakic eye. Ophthalmology 2004; 111:325–331 16. Chung T-Y, Park SC, Lee MO, Ahn K, Chung E-S. Changes in iridocorneal angle structure and trabecular pigmentation with STAAR Implantable Collamer Lens during 2 years. J Refract Surg 2009; 25:251–258 17. Pin˜ero DP, Plaza Puche AB, Alio´ JL. Corneal diameter measurements by corneal topography and angle-to-angle measurements by optical coherence tomography: evaluation of equivalence. J Cataract Refract Surg 2008; 34:126–131 18. Huang D, Schallhorn SC, Sugar A, Farjo AA, Majmudar PA, Trattler WB, Tanzer DJ. Phakic intraocular lens implantation for the correction of myopia; a report by the American Academy of Ophthalmology (Ophthalmic Technology Assessment). Ophthalmology 2009; 116:2244–2258
19. Vilaseca M, Padilla A, Pujol J, Ondategui JC, Artal P, Gu¨ell JL. Optical quality one month after Verisyse and Veriflex phakic IOL implantation and Zeiss MEL 80 LASIK for myopia from 5.00 to 16.50 diopters. J Refract Surg 2009; 25:689–698 20. Muftuoglu O, Alio´ JL. Phakic intraocular lens complications. In: Alio´ JL, Azar DT, eds, Management of Complications in Refractive Surgery. Berlin, Germany, Springer-Verlag, 2008; 225–236 21. Baumeister M, Bu¨hren J, Kohnen T. Position of anglesupported, iris-fixated, and ciliary sulcus-implanted myopic phakic intraocular lenses evaluated by Scheimpflug photography. Am J Ophthalmol 2004; 138:723–731 22. Radhakrishnan S, Rollins AM, Roth JE, Yazdanfar S, Westphal V, Bardenstein DS, Izatt JA. Real-time optical coherence tomography of the anterior segment at 1310 nm. Arch Ophthalmol 2001; 119:1179–1185 23. Pin˜ero DP, Plaza AB, Alio´ JL. Anterior segment biometry with 2 imaging technologies: very-high-frequency ultrasound scanning versus optical coherence tomography. J Cataract Refract Surg 2008; 34:95–102 24. Mu¨ller M, Dahmen G, Po¨rksen E, Geerling G, Laqua H, Ziegler A, Hoerauf H. Anterior chamber angle measurement with optical coherence tomography: intraobserver and interobserver variability. J Cataract Refract Surg 2006; 32:1803–1808 25. Avila M, Li Y, Song JC, Huang D. High-speed optical coherence tomography for management after laser in situ keratomileusis. J Cataract Refract Surg 2006; 32:1836–1842 26. Baikoff G, Lutun E, Wei J, Ferraz C. Contact between 3 phakic intraocular lens models and the crystalline lens: an anterior chamber optical coherence tomography study. J Cataract Refract Surg 2004; 30:2007–2012 27. Baikoff G, Lutun E, Ferraz C, Wei J. Static and dynamic analysis of the anterior segment with optical coherence tomography. J Cataract Refract Surg 2004; 30:1843–1850 28. Ne´meth J, Csa´ka´ny B, Pregun T. Ultrasound biomicroscopic morphometry of the anterior eye segment before and after one drop of pilocarpine. Int Ophthalmol 1996–1997; 20:39–42 29. Kohnen T, Thomala MC, Cichocki M, Strenger A. Internal anterior chamber diameter using optical coherence tomography compared with white-to-white distances using automated measurements. J Cataract Refract Surg 2006; 32:1809–1813 30. Aptel F, Denis P. Optical coherence tomography quantitative analysis of iris volume changes after pharmacologic mydriasis. Ophthalmology 2010; 117:3–10
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First author: Jorge L. Alio´, MD, PhD Keratoconus Unit, Vissum Corporation, Alicante, Spain
Intraocular stability of an angle-supported phakic intraocular lens with changes in pupil diameter Jorge L. Alio´, MD, PhD, David P. Pin˜ero, MSc, Esperanza Sala, OD, Francisco Amparo, MD
PURPOSE: To use anterior segment optical coherence tomography (AS-OCT) to evaluate the stability of a recently released angle-supported phakic intraocular lens (pIOL) in the anterior segment with changes in pupil diameter. SETTING: Keratoconus Unit, Vissum Corporation, Alicante, Spain. METHODS: In this observational cross-sectional study of consecutive eyes with moderate to high myopia, an AcrySof Cachet pIOL was implanted with the aim of minimizing the refractive error. An analysis of the position and stability of the pIOL before and after pharmacologic pupil dilation was performed 3 months postoperatively using the Visante AS-OCT system. A measurement protocol that included several anatomic parameters was developed and applied; the parameter values before and after dilation were compared. RESULTS: Twenty eyes of 20 patients ranging in age from 24 to 48 years old were evaluated. The anterior chamber depth increased significantly with pupil dilation (mean change 0.06 mm G 0.08 [SD]) (P<.01). A significant change was also observed in the distance between the center of the cornea at the endothelial plane and the anterior surface of the pIOL (mean change 0.03 G 0.05 mm) (P Z .01). The distances between the peripheral edges of the pIOL and the corneal endothelium and the distance between the crystalline lens and the pIOL did not change significantly (PR.14). CONCLUSION: The angle-supported pIOL showed excellent intraocular behavior after pupil dilation, with no shortening of the distance between the pIOL and corneal endothelium at the center or peripheral edges of the pIOL. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2010; 36:1517–1522 Q 2010 ASCRS and ESCRS
Over the past decades, studies of phakic intraocular lens (pIOL) implantation1–9 have shown the treatment’s efficacy in the correction of high refractive errors, providing an option to patients who are not suitable candidates for corneal refractive surgery. Phakic IOL implantation has advantages as a refractive procedure because of its potential reversibility, reasonable safety profile, and stability of refractive correction.1–9 Although all pIOLs have been improved to attain better biocompatibility with optimized optical properties,10 complications remain; these include pupil ovalization and corneal endothelial loss.11 Some complications are the result of inadequate selection of pIOL size,2,11 which means the pIOL cannot be customized to the individual eye. Phakic IOLs can be classified into the following 3 categories based on their position in the eye or their mechanism of fixation: anterior chamber angleQ 2010 ASCRS and ESCRS Published by Elsevier Inc.
supported, anterior chamber iris-fixated, and posterior chamber. Several studies of the results of the 3 pIOL models have been published.1–11 A recently released model, the AcrySof Cachet angle-supported pIOL (Alcon, Inc.), is of foldable hydrophobic acrylic, which gives the haptics significant foldability. This would theoretically reduce damage to angle structures and decrease the risk for pupil ovalization when the pIOL is placed in the anterior chamber. Excellent refractive correction and predictability with acceptable safety during the first year of follow-up have been reported.1 In addition, the stability of the pIOL has been corroborated, with minimum or insignificant rotation in a large percentage of cases.1 However, to our knowledge, the stability of this pIOL with changes in pupil diameter has not been evaluated. This is relevant given the characteristics of any anterior chamber angle-supported pIOL and the 0886-3350/$dsee front matter doi:10.1016/j.jcrs.2010.02.028
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position of this pIOL model in the anterior chamber. Indeed, pupil movement has been related to positional changes of other pIOLs in the anterior segment of the eye.12–15 These positional changes could modify the relative position of the pIOL in respect to the corneal endothelium and iridocorneal angle and have the potential to damage anterior chamber structures. New advanced imaging technology, such as veryhigh-frequency ultrasonography16 and optical coherence tomography (OCT),13 allow visualization and characterization of changes in the anterior segment in eyes with IOLs. The aim of the current study was to use anterior segment OCT (AS-OCT) to evaluate the stability of this angle-supported pIOL in the anterior segment with changes in pupil diameter. PATIENTS AND METHODS This observational cross-sectional study included consecutive eyes with moderate to high myopia that had implantation of an AcrySof Cachet pIOL with the aim of minimizing the refractive error. Before surgery, patients were extensively informed about the surgery, its risks, and its benefits, and all signed an informed consent form in accordance with the Declaration of Helsinki. Ethical committee approval was obtained for the study. The inclusion criteria for pIOL implantation and thus for study inclusion were a stable refractive error during the previous 2 years, an endothelial cell count of 2000 cells/mm2 or higher, an anterior chamber depth (ACD) (distance between endothelium and anterior surface of crystalline lens) of 2.8 mm or greater, and no previous or current ocular pathology or cataract.
Surgical Technique The same surgeon (J.L.A.) performed all operations at Vissum Corporation, Instituto Oftalmolo´gico de Alicante, Spain. The pIOL was implanted using a previously described technique.1 The pIOL size was chosen according to preoperative AS-OCT measurement of the horizontal angle-to-angle distance using a previously described measurement procedure (ie, distance between vertex of both iridocorneal angles at the horizontal meridian).17 Postoperative treatment Submitted: January 20, 2010. Final revision submitted: February 10, 2010. Accepted: February 17, 2010. From the Keratoconus Unit (Alio´, Pin˜ero, Sala, Amparo), Vissum Corporation, the Division of Ophthalmology (Alio´), Universidad Miguel Herna´ndez, and the Departamento de O´ptica (Pin˜ero), Farmacologı´a y Anatomı´a, Universidad de Alicante, Alicante, Spain. Supported in part by a grant from the Spanish Ministry of Health, Instituto Carlos III, Red Tema´tica de Investigacio´n Cooperativa en Salud Patologı´a Ocular del Envejecimiento, Calidad Visual y Calidad de Vida, Subproyecto de Calidad Visual (RD07/0062). Corresponding author: Jorge L. Alio´, MD, PhD, Avenida de Denia s/n, Edificio Vissum, 03016 Alicante, Spain. E-mail: [email protected].
Figure 1. Anterior segment OCT analysis of pIOL position under pupil dilation in 1 case shows the following measurements: horizontal pupil size, 6.71 mm; central cornea–pIOL distance, 2.10 mm; temporal cornea–pIOL distance, 1.45 mm; nasal cornea–pIOL distance, 1.43 mm; distance from the vertex of the anterior surface of the crystalline lens and the posterior surface of the pIOL, 1.10 mm; temporal iridocorneal angle, 41.1 degrees; nasal iridocorneal angle, 39.9 degrees.
consisted of dexamethasone 0.1% 3 times a day for 2 weeks and ciprofloxacin 0.3% 3 times a day for 1 week.
Postoperative Examinations The position and stability of the pIOL were evaluated with the Visante AS-OCT system (Carl Zeiss Meditec) 3 months after surgery. The same experienced examiner (E.S.) performed all measurements using the digital tools of the AS-OCT system software. The following parameters were evaluated before pupil dilation (basal conditions, photopic stimulation of the presented optotype) and after pupil dilation with 1 drop of phenylephrine 10% and 1 drop of tropicamide 1%: 1. Horizontal pupil size, which was measured as the distance between temporal and nasal pupil margins. 2. Central ACD, which was measured as the distance from the corneal endothelium to the anterior surface of the crystalline lens. 3. Horizontal angle-to-angle distance, which was measured as the distance between the vertex of the temporal and nasal iridocorneal angles. 4. Distance from the anterior surface of the pIOL and the corneal endothelium at different points (center, temporal, and nasal edges of the anterior surface of the pIOL). These distances were measured over a line perpendicular to the curvature of the posterior cornea (central cornea–pIOL distance, temporal cornea–pIOL distance, nasal cornea– pIOL distance). 5. Distance from the vertex of the anterior surface of the crystalline lens and the posterior surface of the pIOL (crystalline lens–pIOL distance) over a line perpendicular to the surface of the pIOL. 6. Temporal and nasal iridocorneal angles. Figure 1 shows an AS-OCT image of measurements of these parameters. All measurements under pupil dilation were performed 20 minutes after drop instillation.
Statistical Analysis Statistical analysis was performed using SPSS software for Windows (version 15.0, SPSS, Inc.). Normality of the data
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Table 1. Comparison of changes before and after pharmacologic pupil dilation.
Parameter
Before Pupil Dilation
Horizontal pupil size (mm) Mean G SD 4.36 C 0.86 Range 2.47 to 6.20 Central ACD (mm) Mean G SD 3.21 C 0.27 Range 2.80 to 3.67 Horizontal ATA distance (mm) Mean G SD 12.08 C 0.44 Range 11.13 to 13.01 Central cornea–pIOL distance (mm) Mean G SD 2.03 C 0.25 Range 1.55 to 2.47 Temporal cornea–pIOL distance (mm) Mean G SD 1.44 C 0.22 Range 1.07 to 1.80 Nasal cornea–pIOL distance (mm) Mean G SD 1.44 C 0.22 Range 0.96 to 1.76 Crystalline lens–pIOL distance (mm) Mean G SD 0.94 C 0.19 Range 0.45 to 1.41 Temporal iridocorneal angle (degrees) Mean G SD 38.24 C 8.76 Range 26.10 to 60.50 Nasal iridocorneal angle (degrees) Mean G SD 37.61 C 7.68 Range 26.30 to 54.00
After Pupil Dilation
P Value !.01
6.57 C 0.75 4.50 to 7.65 !.01 3.27 C 0.23 2.92 to 3.60 .14 12.18 C 0.46 11.18 to 12.77 .01 2.07 C 0.26 1.61 to 2.53 .16 1.46 C 0.19 1.16 to 1.75 .30 1.46 C 0.23 1.00 to 1.80 .43 0.95 C 0.21 0.35 to 1.43 !.01 45.98 C 7.92 32.70 to 64.58 !.01 43.43 C 7.39 30.40 to 58.40
ACD Z anterior chamber depth; ATA Z angle-to-angle; pIOL Z phakic intraocular lens
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distance (0.09 G 0.27 mm) with dilation was not statistically significant (P Z .14). Regarding the position of the pIOL in the anterior chamber, a significant change was only observed in the distance between the center of the cornea at the endothelial plane and the anterior surface of the pIOL (mean change 0.03 G 0.05 mm) (P Z .01). The other parameters characterizing the pIOL position did not change significantly with pupil dilation (PR.14) (Table 1). Evaluation of the relationship between the changes in anatomic parameters and the baseline values showed a statistically significant correlation between pupil change and pupil diameter before dilation (r Z 0.650, P!.01). The change in ACD with pharmacologic pupil dilation was significantly correlated with the baseline values of the following parameters characterizing the position of the pIOL: central cornea–pIOL distance (r Z 0.549, P Z .01), temporal cornea–pIOL distance (r Z 0.610, P!.01), and nasal cornea–pIOL distance (r Z 0.534, P Z .02) (Figure 2). Other statistically significant correlations were between the change in ACD and the baseline ACD (r Z 0.515, P Z .02) and between the change in temporal cornea–pIOL distance and the baseline temporal cornea–pIOL distance (r Z 0.527, P Z .02). Figure 3 shows an example of the positional changes of the pIOL after pharmacologic dilation in 1 case. The images show an increase in the distance between the pIOL and the corneal endothelium at the center as well as the opening of the iridocorneal angles. DISCUSSION
samples was first checked by the Kolmogorov-Smirnov test. The use of parametric statistics was always possible because all data samples followed a normal distribution; therefore, the Student t test for paired data was used for all parameter comparisons before and after pupil dilation with the same level of significance (P!.05). Pearson correlation coefficients were used to assess the correlation between variables. The mean values G SD are given.
RESULTS The study evaluated 20 consecutive eyes (13 right, 7 left) of 20 patients. The patients ranged in age from 24 to 48 years. Table 1 shows the changes in anatomic parameters after pupil dilation. As expected, the pupil size increased significantly (mean change 2.21 G 0.63 mm) and the temporal and nasal iridocorneal angles became significantly wider (mean change 7.75 G 6.54 degrees and 5.82 G 5.89 degrees, respectively) after pharmacologic dilation (all P!.01). The ACD also increased significantly (mean change 0.06 G 0.08 mm) (P!.01). The mean change in the angle-to-angle
Phakic IOLs have been shown to be useful in the correction of moderate to high myopia.1–9 Implantation of pIOLs leads to better postoperative quality of vision than keratorefractive excimer laser surgery in the same myopic eyes.18,19 However, questions remain about the potential long-term risks to anterior segment structures. Phakic IOLs should be well positioned with adequate stability so they do not damage the corneal endothelium and anterior lens capsule.10,11,20 Therefore, stability of the pIOL in relationship to the intraocular structures is crucial to good performance over time because a lack of stability is directly related to complications. Baumeister et al.21 found no significant movement of 2 anterior chamber IOLs (Artisan, Ophtec; NuVita, Bausch & Lomb) in an anteroposterior direction at 3 months and 12 months, whereas a posterior chamber pIOL (Implantable Collamer Lens, Staar Surgical Co.) showed significant movement toward the crystalline lens. A change in pIOL position can lead to complications, such as endothelial
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Figure 2. Scattergrams of the relationship between the change in the ACD with pharmacologic dilation and baseline values of parameters characterizing the position of the pIOL in the eye. A: Distance from the center of the anterior surface of the pIOL to the corneal endothelium (CCLD). B: Distance from the temporal edge of the anterior surface of the pIOL to the corneal endothelium (TCLD). C: Distance from the nasal edge of the anterior surface of the pIOL to the corneal endothelium (NCLD). The adjusting line to the data obtained by means of the least-squares fit is shown in all the graphs and was calculated as follows: Change in ACD (mm) Z 0.18 CCLD (mm) C 0.13 (r2 Z 0.301); change in ACD (mm) Z 0.24 TCLD (mm) C 0.40 (r2 Z 0.372); and change in ACD (mm) Z 0.21 NCLD (mm) C 0.36 (r2 Z 0.285).
damage; a reason for the change is the dynamics of the pIOL as the pupil size changes. Several studies12–15 report that some pIOL models change position with pupil movement. For example, Cruysberg et al.12 found a decrease in the distance between an irisfixated pIOL and the crystalline lens, suggesting posterior displacement of the pIOL with dark-induced pupil dilation, as well as an increase in the distance between the pIOL and the corneal endothelium. In a study by Petternel et al.,15 copolymer posterior chamber pIOLs moved backward after pilocarpine instillation while the distance between the pIOL and crystalline lens decreased under natural photopic conditions. However, to our knowledge, changes in the position of angle-supported pIOLs with pupil size modifications have not been reported. Thus, we used AS-OCT to evaluate the stability of a recently released angle-supported pIOL in the anterior segment after pharmacologic pupil dilation. The AS-OCT system we used to characterize the anterior segment and the position of the pIOL in the eye allows visualization and evaluation of all anterior
segment structures in front of the iris22 but cannot detect structures behind pigmented tissue such as the iris23 (less useful for posterior chamber evaluation). Anterior segment OCT has a resolution similar to that of ultrasound devices (approximately 20 mm) and excellent repeatability.23,24 The applications described for AS-OCT include analysis of the position of pIOLs.13,25,26 Considering the advantages of ASOCT imaging technology and based on the objectives of our study and the type of pIOL we analyzed (angle-supported anterior chamber), we believed the technology would provide a valid tool for our purposes. We developed a protocol to evaluate the position of the pIOL with the AS-OCT system. The protocol included the following parameters: distance from the anterior surface of the pIOL to the corneal endothelium at different points, distance from the vertex of the anterior surface of the crystalline lens to the posterior surface of the pIOL, and anterior segment feature (ACD, angle-to-angle distance, and iridocorneal angles). Regarding the anatomic changes in the anterior segment with pupil dilation, we found a small but
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Figure 3. Example of the positional changes of the angle-supported pIOL after pharmacologic dilation in 1 specific case. Top: Before pupil dilation. Bottom: After pupil dilation. Note the increase in the distance between the pIOL and the corneal endothelium at the center and the opening of the iridocorneal angles.
statistically significant increase in ACD. This finding is consistent with anterior segment changes related to pupil size modifications reported by other authors.27,28 In a study by Baikoff et al.,27 with 1.00 diopter of accommodation and the corresponding miosis (mean pupil diameter decrease 0.15 mm), the anterior pole moved forward by a mean of 30 mm, with a decrease (approximately 0.3 mm) in the radius of curvature of the anterior surface of the crystalline lens. Therefore, it seems as though changes in ACD are related to changes in the shape of the anterior surface of the crystalline lens. On the other hand, iridocorneal angles (temporal and nasal) increased significantly with pupil dilation. This finding seems logical: As the anterior surface of the crystalline lens became flatter, the iris moved backward, opening the angle. This is consistent with outcomes in a previous study28 in which wide chamber angles had a tendency to become narrower and narrow angles to become wider after instillation of pilocarpine. (We included only patients with wide iridocorneal angles.) A possible reason for this tendency is the change in iris volume that occurs with pupil dilation.29 Furthermore, we found no significant changes in the horizontal diameter of the anterior chamber (angle-to-angle distance), and our mean
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values before and after pupil dilation are consistent with those reported in the literature.17,30 Regarding the position of the pIOL, we found no significant changes in the distances between the edges of the anterior surface of the pIOL and the corneal endothelium, which implies that with pupil dilation, the relative position of the periphery of the pIOL and the corneal endothelium is stable. Phakic IOLs to correct high myopia are thicker in the periphery than in the center. Therefore, it is crucial to maintain the peripheral edges of the pIOL as far as possible from the corneal endothelium in all physiologic ocular conditions, such as pupil changes or accommodation. The distance between the center of the pIOL and the corneal endothelium increased significantly, although the change was of small magnitude, as with the ACD. Therefore, it seems the 2 types of changes occur simultaneously; that is, a change in the position of the central portion of the pIOL due to a change in the pIOL curvature in this area. In addition, the anterior crystalline lens curvature also changed as a result of the cycloplegic effect; therefore, the distance between the crystalline lens and the back surface of the pIOL did not change significantly with pupil dilation, as expected. The pIOL we used is flexible; therefore, its curvature is probably modified slightly with backward movement of the iris and flattening of the anterior surface of the crystalline lens. In conclusion, the AcrySof Cachet pIOL showed excellent intraocular behavior after pupil dilation, with no shortening of the distance between the pIOL and the corneal endothelium at the center or peripheral edges of the pIOL. Although there was a slight tendency for the central pIOL to move backward after pharmacologic dilation, the distance between the pIOL edges and the endothelium remained constant. Therefore, sufficient space was maintained between the pIOL and the anterior segment structures after pupil dilation, preventing the possibility of unwanted pIOL contact with ocular structures. Future studies should evaluate the potential refractive and optical effects of modification of the central area of the pIOL. REFERENCES 1. Kohnen T, Knorz MC, Cochener B, Gerl RH, Arne´ J-L, Colin J, Alio´ JL, Bellucci R, Marinho A. AcrySof phakic angle-supported intraocular lens for the correction of moderate-to-high myopia: one-year results of a multicenter European study. Ophthalmology 2009; 116:1314–1321 2. Alio´ JL, Pin˜ero D, Bernabeu G, Galal A, Vargas JM, Ismail MM. The Kelman Duet phakic intraocular lens: 1-year results. J Refract Surg 2007; 23:868–879 3. Benedetti S, Casamenti V, Marcaccio L, Brogioni C, Assetto V. Correction of myopia of 7 to 24 diopters with the Artisan phakic intraocular lens: two-year follow-up. J Refract Surg 2005; 21:116–126
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4. Leccisotti A, Fields SV. Clinical results of ZSAL-4 angle-supported phakic intraocular lenses in 190 myopic eyes. J Cataract Refract Surg 2005; 31:318–323 5. Alio´ JL, Mulet ME, Shalaby AMM. Artisan phakic iris claw intraocular lens for high primary and secondary hyperopia. J Refract Surg 2002; 18:697–707 6. Allemann N, Chamon W, Tanaka HM, Mori ES, Campos M, Schor P, Baikoff G. Myopic angle-supported intraocular lenses; two-year follow-up. Ophthalmology 2000; 107:1549–1554 7. Pe´rez-Santonja JJ, Alio´ JL, Jime´nez-Alfaro I, Zato MA. Surgical correction of severe myopia with an angle-supported phakic intraocular lens. J Cataract Refract Surg 2000; 26:1288–1302 8. Alio´ JL, de la Hoz F, Pe´rez-Santonja JJ, Ruiz-Moreno JM, Quesada JA. Phakic anterior chamber lenses for the correction of myopia; a 7-year cumulative analysis of complications in 263 cases. Ophthalmology 1999; 106:458–466 9. Baikoff G, Arne JL, Bokobza Y, Colin J, George JL, Lagoutte F, Lesure P, Montard M, Saragoussi JJ, Secheyron P. Angle-fixated anterior chamber phakic intraocular lens for myopia of 7 to 19 diopters. J Refract Surg 1998; 14:282–293 10. Alio JL. Advances in phakic intraocular lenses: indications, efficacy, safety, and new designs. Curr Opin Ophthalmol 2004; 15: 350–357 11. Chang DH, Davis EA. Phakic intraocular lenses. Curr Opin Ophthalmol 2006; 17:99–104 12. Cruysberg LPJ, Doors M, Berendschot TTJM, De Brabander J, Webers CAB, Nuijts RMMA. Iris-fixated anterior chamber phakic intraocular lens for myopia moves posteriorly with mydriasis. J Refract Surg 2009; 25:394–396 13. Koivula A, Kugelberg M. Optical coherence tomography of the anterior segment in eyes with phakic refractive lenses. Ophthalmology 2007; 114:2031–2037 14. Maldonado MJ, Garcı´a-Feijoo´ J, Benı´tez Del Castillo JM, Teutsch P. Cataractous changes due to posterior chamber flattening with a posterior chamber phakic intraocular lens secondary to the administration of pilocarpine. Ophthalmology 2006; 113:1283–1288 15. Petternel V, Ko¨ppl C-M, Dejaco-Ruhswurm I, Findl O, Skorpik C, Drexler W. Effect of accommodation and pupil size on the movement of a posterior chamber lens in the phakic eye. Ophthalmology 2004; 111:325–331 16. Chung T-Y, Park SC, Lee MO, Ahn K, Chung E-S. Changes in iridocorneal angle structure and trabecular pigmentation with STAAR Implantable Collamer Lens during 2 years. J Refract Surg 2009; 25:251–258 17. Pin˜ero DP, Plaza Puche AB, Alio´ JL. Corneal diameter measurements by corneal topography and angle-to-angle measurements by optical coherence tomography: evaluation of equivalence. J Cataract Refract Surg 2008; 34:126–131 18. Huang D, Schallhorn SC, Sugar A, Farjo AA, Majmudar PA, Trattler WB, Tanzer DJ. Phakic intraocular lens implantation for the correction of myopia; a report by the American Academy of Ophthalmology (Ophthalmic Technology Assessment). Ophthalmology 2009; 116:2244–2258
19. Vilaseca M, Padilla A, Pujol J, Ondategui JC, Artal P, Gu¨ell JL. Optical quality one month after Verisyse and Veriflex phakic IOL implantation and Zeiss MEL 80 LASIK for myopia from 5.00 to 16.50 diopters. J Refract Surg 2009; 25:689–698 20. Muftuoglu O, Alio´ JL. Phakic intraocular lens complications. In: Alio´ JL, Azar DT, eds, Management of Complications in Refractive Surgery. Berlin, Germany, Springer-Verlag, 2008; 225–236 21. Baumeister M, Bu¨hren J, Kohnen T. Position of anglesupported, iris-fixated, and ciliary sulcus-implanted myopic phakic intraocular lenses evaluated by Scheimpflug photography. Am J Ophthalmol 2004; 138:723–731 22. Radhakrishnan S, Rollins AM, Roth JE, Yazdanfar S, Westphal V, Bardenstein DS, Izatt JA. Real-time optical coherence tomography of the anterior segment at 1310 nm. Arch Ophthalmol 2001; 119:1179–1185 23. Pin˜ero DP, Plaza AB, Alio´ JL. Anterior segment biometry with 2 imaging technologies: very-high-frequency ultrasound scanning versus optical coherence tomography. J Cataract Refract Surg 2008; 34:95–102 24. Mu¨ller M, Dahmen G, Po¨rksen E, Geerling G, Laqua H, Ziegler A, Hoerauf H. Anterior chamber angle measurement with optical coherence tomography: intraobserver and interobserver variability. J Cataract Refract Surg 2006; 32:1803–1808 25. Avila M, Li Y, Song JC, Huang D. High-speed optical coherence tomography for management after laser in situ keratomileusis. J Cataract Refract Surg 2006; 32:1836–1842 26. Baikoff G, Lutun E, Wei J, Ferraz C. Contact between 3 phakic intraocular lens models and the crystalline lens: an anterior chamber optical coherence tomography study. J Cataract Refract Surg 2004; 30:2007–2012 27. Baikoff G, Lutun E, Ferraz C, Wei J. Static and dynamic analysis of the anterior segment with optical coherence tomography. J Cataract Refract Surg 2004; 30:1843–1850 28. Ne´meth J, Csa´ka´ny B, Pregun T. Ultrasound biomicroscopic morphometry of the anterior eye segment before and after one drop of pilocarpine. Int Ophthalmol 1996–1997; 20:39–42 29. Kohnen T, Thomala MC, Cichocki M, Strenger A. Internal anterior chamber diameter using optical coherence tomography compared with white-to-white distances using automated measurements. J Cataract Refract Surg 2006; 32:1809–1813 30. Aptel F, Denis P. Optical coherence tomography quantitative analysis of iris volume changes after pharmacologic mydriasis. Ophthalmology 2010; 117:3–10
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First author: Jorge L. Alio´, MD, PhD Keratoconus Unit, Vissum Corporation, Alicante, Spain