Rotational stability is essential for a toric intraocular lens (IOL) to adequately correct corneal astigmatism. It is estimated that approximately 22% of cataract surgery candidates exhibit corneal astigmatism exceeding 1.50 diopters (D).1 Uncorrected astigmatism reduces visual acuity and increases spectacle dependence, which may reduce quality of life2 and ability to undertake daily tasks3 and potentially increase economic costs.4 Correcting astigmatism at the time of surgery removes the problem of meridonal magnification caused by spectacle astigmatic correction, which distorts shape and affects spatial perception.5 Surgeons may use corneal or limbal relaxing incisions6,7 to reduce postoperative astigmatism following cataract surgery or implant a toric intraocular lens (IOL). Correction of corneal astigmatism relies on a predictable corneal healing response, but this can often be variable, particularly with high levels of astigmatism.8 Toric IOLs may thus offer a potentially more stable correction of astigmatism when correctly positioned with minimal rotation.
A sinusoidal relationship exists between the magnitude of axis misalignment and the residual cylinder power.9 Small deviations from the correct axis will reduce the effective power of the cylinder. For example, a rotation of 30° off-axis after surgery will negate correction of the astigmatic power and shift the resultant cylinder to a new axis.10 Toric IOLs have previously been associated with rotational instability, but the incidence of postoperative axis rotation of IOLs has reduced with newer designs11 along with techniques developed to better correct for eye and head rotation.12
Digital imaging has previously been applied to toric IOL rotation, but has been limited by image quality13 and has not compensated for eye or head rotation between consecutive visits.14,15 Any eye or head rotation during photography can lead to overestimation or underestimation of IOL rotation and thus must be compensated for. To do this, the use of anatomical markers such as iris features or conjunctival vessels is recommended.12 The American National Standards Institute guidelines for toric IOL rotational stability specify that 90% of eyes should be in the order of 5° or less on visits at least 3 months apart. Currently only the Tecnis IOL (AMO, Abbott Park, IL) has been shown to meet this standard.16 The purpose of the current study was to determine the rotational stability and centration using objective image analysis of a new toric lens design platform.
Patients and Methods
For the study, 66 healthy patients (mean age: 69.92 ± 8.45 years, 42 women and 24 men) were implanted with the monofocal Rayner 600S IOL (Rayner, Worthing, United Kingdom) in one eye only. All participants were recruited and examined at the Queen Elizabeth Hospital (University Hospitals Birmingham NHS Foundation Trust) in Birmingham, United Kingdom.
The 600S IOL is an aberration neutral lens formed of a hydrophilic material based on the existing C-flex design by Rayner. It has an optic diameter of 6 mm and a 360° square edge on both the anterior and posterior surfaces supported by C-loop haptics. The lens optic also features engraved markings to assist stability measurement (Figure A, available in the online version of this article).
The 600S intraocular monofocal lens (Rayner, Worthing, United Kingdom) with engraved lines to aid rotational alignment.
Inclusion criteria for the study consisted of patients older than 40 years recommended for routine cataract surgery with otherwise clear media and healthy eyes who exhibited less than 1.50 diopters (D) cylinder of astigmatism. Exclusion criteria comprised previous ocular surgery or trauma, ocular inflammation, age older than 85 years, binocular vison anomalies, amblyopia, and insufficient physical or mental conditions to allow participation. The study conformed to the tenets of the Declaration of Helsinki and was approved by the ethical committees of both Aston University and the University Hospitals Birmingham Trust.
Routine phacoemulsification and IOL implantation was performed by the same surgeon (SK) for all recruited patients after receiving informed consent. All surgeries were uneventful with no intraoperative complications.
Following surgery and implantation, postoperative photographs were taken using the Keeler Symphony digital slit lamp (Keeler Ltd, Windsor, United Kingdom) of the lens in situ. Photography took place 1 hour after surgery and on follow-up visits conducted at 1 to 3 days, 30 days, and 90 to 180 days postoperatively. Maximal dilation was required for imagery and was achieved using 1% tropicamide and 2.5% phenylephrine at each visit. No significant postoperative complications were encountered other than mild posterior capsular opacification in two participants at the 180 day visit, but this did not affect imaging.
All images were photographed at a magnification of ×10 using retroillumination and analyzed using specialist software (Labview; National Instruments, Austin, TX). Rotation and centration were determined for each postoperative visit (Figure 1A). The axis of IOL rotation was measured by drawing a line adjoining the two IOL orientation markings. Head and eye rotation was then compensated for by comparing this to the axis of a line drawn joining two consistently visible iris features or conjunctival vessels (Figure 1B). Anatomical markers were carefully chosen to ensure visibility on each photograph throughout the follow-up period. The angle between the two lines determined the axis of alignment at each time point and was compared to that of each visit to determine rotation. To measure IOL centration, the center of a circle circumscribing the IOL optic edge, pupil margin, and limbus were compared12 (Figure 1C).
Image analysis for rotation and centration. (A) Original image of intraocular lens in situ, circumference of lens, and engraved markings clearly visible. (B) Line drawn joining engravings and separate line drawn joining two clearly visible conjunctival vessels. The angle between these lines is measured and compared at each visit to determine rotation. (C) Circle drawn to circumscribe the lens optic edge and one to circumscribe the limbus. Centers are compared for each visit to determine centration.
Rotation stability and IOL centration were assessed at each follow-up visit by subtracting from the values obtained at 1 to 3 days. The data were found to be normally distributed using a Kolmogorov–Smirnov test (P > .05) and therefore repeated measure analysis of variance was used to examine differences between visits.
Surgery was uneventful with no intraoperative complications. Average monocular CDVA improved from 0.50 ± 0.28 logMAR (range: 0.00 to 1.47 logMAR) preoperatively to −0.02 ± 0.05 logMAR following surgery. Preoperative and postoperative manifest refraction were performed by the same clinician. The mean pre-operative spherical equivalent was 2.56 ± 2.23 D and improved postoperatively to a reduced mean spherical equivalent of 0.46 ± 0.34 D.
Mean rotation at each follow-up visit is shown in Figure 2. The average rotation was −0.03° ± 1.97° (absolute values: 1.60° ± 1.13°) from immediately after surgery to 1 day, 0.04° ± 2.09° (absolute values: 1.58° ± 1.36°) from 1 to 30 days, and −0.10° ± 2.34° (absolute values: 1.83° ± 1.44°) from 90 to 180 days. No clinically significant difference was found in rotation between visits (F = 0.041, P = .960).
Rotation (degrees) of the 600S intraocular lens (Rayner, Worthing, United Kingdom) at each postoperative visit.
Minus signs indicate anticlockwise rotation but, as can be concluded from the average rotation results, no real bias was found in the direction of rotation with the IOL. The average centration relative to the limbus after surgery was −0.04 ± 0.25 mm horizontally and 0.04 ± 0.26 mm vertically at 1 to 3 days, 0.00 ± 0.38 mm vertically and 0.01 ± 0.28 mm horizontally at 30 days, and 0.08 ± 0.37 mm vertically and 0.07 ± 0.47 mm horizontally at 90 to 180 days. Data show average centration to be relatively minimal and hence stable. Negative numbers here indicate temporal or superior displacement.
Decentration (Figure 3) at each stage remained within 0.5 mm. Vertical decentration at 1 to 3 days was 0.04 ± 0.26 mm vertically and −0.04 ± 0.25 mm horizontally. This reduced to 0.00 ± 0.38 mm vertically and 0.01 ± 0.28 mm horizontally at 30 days, and 0.08 ± 0.37 mm vertically and 0.07 ± 0.47 mm horizontally at 90 to 180 days. Generally, decentration remained inferior and nasal but showed no significant change from immediately after surgery to 90 to 180 days (F = 1.872, P = .136) and was similar in magnitude horizontally to vertically (F = 3.474, P = .067).
Decentration of the 600S intraocular lens (Rayner, Worthing, United Kingdom) at each postoperative visit.
At least one-quarter of patients undergoing cataract surgery have the potential to benefit from toric IOLs.1 The stability of toric IOLs has long been of concern to surgeons due to their susceptibility to rotate after implantation. In cases of significant deviation from the axis of correction, surgical repositioning is required, which must be performed within 1 month after implantation. Studies have reported significant rotation in the range of 10% to 67% with toric IOLs.17–19 However, not all studies correct for cyclorotation of the eye or head tilt, which will affect results.
Various anatomical features may affect rotational stability (eg, capsular bag size19 and longer axial length20). In the current study, average axial length was measured as 23.38 ± 1.47 mm (range: 20.93 to 27.40 mm) with a correlation coefficient value of 0.02 (P > .05) and so was unlikely to have an impact on the small rotation reported. Aspects of IOL design such as haptic type can also influence stability. Plate haptics in general have shown better long-term stability, but exhibit greater rotation in the early postoperative period compared to loop haptics.21–24 Newer designs have been introduced to provide mini-loop and Z-haptics to provide better stability.11,25,26 It is thought the plate haptic design of the 600S may have contributed to its high level of stability within the study.
Early postoperative rotation may be due to movement of the IOL haptics prior to fusion with the capsular bag, but increasing friction may reduce this occurrence. Using a larger diameter IOL may be helpful, but care must be taken not to stretch the capsular bag, which can lead to more rotation.27 Haptic material can also affect stability; polymethylmethacrylate has been shown to provide the best stability and silicone the poorest.28
Improvements have been made to toric IOLs in recent years, with newer designs showing better stability. Mean absolute rotation has been reported in a variety of toric IOLs and ranges from 1° to 5° (Table A, available in the online version of this article) in recent publications. The American National Standards Institute guideline is currently met only by the Tecnis toric IOL.16
Recent Studies Investigating Toric IOLs and the Results of Mean Absolute Rotation Values and Range Over Specific Time Periods
Previous studies have assessed toric IOL rotation subjectively, often through slit-lamp beam protractors or graticules within eye pieces of slit-lamp biomicroscopes.15,25,29 However, stable head and eye position is vital for accurate measurements. Separate mounted cameras15 can also introduce another source of error in rotation measurements, but this can be eliminated through the use of integrated cameras in digital slit-lamp biomicroscopes.
Subjective techniques may only estimate rotation to the nearest 1° to 5°.12 The form of objective analysis used in the current study has been shown to have repeatability of 1° for rotation, 2° for head rotation, and 0.1 mm for centration.12 However, image quality is paramount because poor pupil dilation and fibrosis in later stages may obscure the view of toric markings. Sufficient mydriasis may present as a particular difficulty in older populations and was a significant limitation in the study. Simultaneous imaging of the iris or conjunctiva and toric engravings required increased illumination, which resulted in some patient discomfort and squinting, hence obscuring the toric markings.
Emerging technologies to assess rotation include optical coherence tomography, which has been demonstrated as a potential aid for aligning toric IOLs and measuring postoperative rotation.38 Although this method can both assist IOL alignment and evaluate rotational stability, it is limited by the requirement to obtain simultaneous images of the iris and corneal topography and cannot compensate for errors due to IOL decentration or tilt. It is also reliant on marked characteristics in the mid-peripheral iris, unlike the technique in the current study where reference points at any location on the iris can be used. Pronounced senile rings in the elderly could thus pose an issue with optical coherence tomography. The use of biological markers is also supported by Sanders et al.,39 who reported ease and precision while compensating for head and rotation using similar photography methodology.
The objective analysis implemented proved to allow sensitive measurement of stability while adequately compensating for factors that could influence results. Rotation of the 600S IOL was minimal across the visits and never exceeded 5° at any point; the C-loop haptic design may have contributed this. Centration was also stable after implantation. The Rayner 600S IOL has thus shown to be an ideal platform for toric correction meeting the U.S. Food and Drug Administration prescribed American National Standards Institute guidelines for toric IOL rotational stability.
- Ferrer-Blasco T, Montés-Micó R, Peixoto-de-Matos SC, et al. Prevalence of corneal astigmatism before cataract surgery. J Cataract Refract Surg. 2009;35:70–75. doi:10.1016/j.jcrs.2008.09.027 [CrossRef]
- Pesudovs K, Garamendi E, Elliott DB. A quality of life comparison of people wearing spectacles or contact lenses or having undergone refractive surgery. J Refract Surg. 2006;22:19–27. doi:10.3928/1081-597X-20060101-07 [CrossRef]
- Wolffsohn JS, Bhogal G, Shah S. Effect of uncorrected astigmatism on vision. J Cataract Refract Surg. 2011;37:454–460. doi:10.1016/j.jcrs.2010.09.022 [CrossRef]
- Laurendeau C, Lafuma A, Berdeaux G. Modelling lifetime cost consequences of toric compared with standard IOLs in cataract surgery of astigmatic patients in four European countries. J Med Econ. 2009;12:230–237. doi:10.3111/13696990903257439 [CrossRef]
- Guyton DL. Prescribing cylinders: the problem of distortion. Surv Ophthalmol. 1977;22:177–188. doi:10.1016/0039-6257(77)90054-6 [CrossRef]
- Mendicute J, Irigoyen C, Ruiz M, Griffiths M. Toric intraocular lens versus opposite clear corneal incisions to correct astigmatism in eyes having cataract surgery. J Cataract Refract Surg. 2009;35:451–458. doi:10.1016/j.jcrs.2008.11.043 [CrossRef]
- Sun XY, Vicary D, Montgomery P, et al. Toric intraocular lenses for correcting astigmatism in 130 eyes. Ophthalmology. 2000;107:1776–1781. doi:10.1016/S0161-6420(00)00266-9 [CrossRef]
- Tehrani M, Dick HB. Incisional keratotomy to toric intraocular lenses: an overview of the correction of astigmatism in cataract and refractive surgery. Int Ophthalmol Clin. 2003;43:43–52. doi:10.1097/00004397-200343030-00005 [CrossRef]
- Ma JJ, Tseng SS. Simple method for accurate alignment in toric phakic and aphakic intraocular lens implantation. J Cataract Refract Surg. 2008;34:1631–1636. doi:10.1016/j.jcrs.2008.04.041 [CrossRef]
- Novis C. Astigmatism and toric intraocular lenses. Curr Opin Ophthalmol. 2000;11:47–50. doi:10.1097/00055735-200002000-00007 [CrossRef]
- Buckhurst PJ, Wolffsohn JS, Naroo SA, Davies LN. Rotational and centration stability of an aspheric intraocular lens with a simulated toric design. J Cataract Refract Surg. 2010;36:1523–1528. doi:10.1016/j.jcrs.2010.03.047 [CrossRef]
- Wolffsohn JS, Buckhurst PJ. Objective analysis of toric intraocular lens rotation and centration. J Cataract Refract Surg. 2010;36:778–782. doi:10.1016/j.jcrs.2009.12.027 [CrossRef]
- Weinard F, Jung A, Stein A, et al. Rotational stability of a single-piece hydrophobic acrylic intraocular lens: new method for high-precision rotation control. J Cataract Refract Surg. 2007;33:800–803. doi:10.1016/j.jcrs.2007.01.030 [CrossRef]
- Nguyen TM, Miller KM. Digital overlay technique for documenting toric intraocular lens axis orientation. J Cataract Refract Surg. 2007;26:1496–1504. doi:10.1016/S0886-3350(00)00442-9 [CrossRef]
- Viestenz A, Seitz B, Langenbucher A. Evaluating the eye's rotational stability during standard photography: effect on determining the axial orientation of toric intraocular lenses. J Cataract Refract Surg. 2005;31:557–561. doi:10.1016/j.jcrs.2004.07.019 [CrossRef]
- Waltz KL, Featherstone K, Tsai L, Trentacost O. Clinical outcomes of TECNIS toric intraocular lens implantation after cataract removal in patients with corneal astigmatism. Ophthalmology. 2015;122:39–47. doi:10.1016/j.ophtha.2014.06.027 [CrossRef]
- Till JS, Yoder PR Jr, Wilcox TK, Spielman JL. Toric intraocular lens implantation: 100 consecutive cases. J Cataract Refract Surg. 2002;28:295–301. doi:10.1016/S0886-3350(01)01035-5 [CrossRef]
- Warlo I, Krummenauer F, Dick HB. Rotational stability in intraocular lenses with C-loop haptics versus Z haptics in cataract surgery: a prospective randomised comparison [article in German]. Ophthalmologe. 2005;102:987–999. doi:10.1007/s00347-005-1213-7 [CrossRef]
- Chang DF. Early rotational stability of the longer Staar toric intraocular lens: fifty consecutive cases. J Cataract Refract Surg. 2003;29:935–940. doi:10.1016/S0886-3350(02)01843-6 [CrossRef]
- Shah GD, Praveen MR, Vasavada AR, et al. Rotational stability of a toric intraocular lens: influence of axial length and alignment in the capsular bag. J Cataract Refract Surg. 2012;38:54–59. doi:10.1016/j.jcrs.2011.08.028 [CrossRef]
- Patel CK, Ormonde S, Rosen PH, et al. Postoperative intraocular lens rotation: a randomized comparison of plate and loop haptic implants. Ophthalmology. 1999;106:2190–2196. doi:10.1016/S0161-6420(99)90504-3 [CrossRef]
- Prinz A, Neumayer T, Buehl W, et al. Rotational stability and posterior capsule opacification of a plate-haptic and an open-loop-haptic intraocular lens. J Cataract Refract Surg. 2011;37:251–257. doi:10.1016/j.jcrs.2010.08.049 [CrossRef]
- Grabow HB. Toric intraocular lens report. Annals of Ophthalmology and Glaucoma. 1997;29:161–163.
- Pärssinen O, Räty J, Vainikainen J, et al. Compression forces of haptics of freely rotating posterior chamber intraocular lenses. J Cataract Refract Surg. 1998;24:415–425. doi:10.1016/S0886-3350(98)80334-9 [CrossRef]
- De Silva DJ, Ramkissoon YD, Bloom PA. Evaluation of a toric intraocular lens with a Z-haptic. J Cataract Refract Surg. 2006;32:1492–1498. doi:10.1016/j.jcrs.2006.04.022 [CrossRef]
- Kent DG, Peng Q, Isaacs RT, et al. Mini-haptics to improve capsular fixation of plate-haptic silicone intraocular lenses. J Cataract Refract Surg. 1998;24:666–671. doi:10.1016/S0886-3350(98)80263-0 [CrossRef]
- Bylsma S. The STAAR Toric IOL: current technique and results with a plate-haptic lens that effectively neutralizes corneal astigmatism at the time of cataract surgery. Cataract & Refractive Surgery Today. 2006:74–76.
- Oshika T, Nagata T, Ishii Y. Adhesion of lens capsule to intraocular lenses of polymethylmethacrylate, silicone, and acrylic foldable materials: an experimental study. Br J Ophthalmol. 1998;82:549–553. doi:10.1136/bjo.82.5.549 [CrossRef]
- Ruhswurm I, Scholz U, Zehetmayer M, et al. Astigmatism correction with a foldable toric intraocular lens in cataract patients. J Cataract Refract Surg. 2000;26:1022–1027. doi:10.1016/S0886-3350(00)00317-5 [CrossRef]
- Grohlich M, Miháltz K, Lasta M, et al. Evaluation of postoperative astigmatism correction and postoperative rotational stability of two toric intraocular lenses [article in German]. Klin Monbl Augenheilkd. 2017;234:796–804.
- Gyöngyössy B, Jirak P, Schönher U. Long-term rotational stability and visual outcomes of a single-piece hydrophilic acrylic toric IOL: a 1.5-year follow-up. Int J Ophthalmol. 2017;10:573–578.
- Ferreira TB, Berendschot TT, Ribeiro FJ. Clinical outcomes after cataract surgery with a new transitional toric intraocular lens. J Refract Surg. 2016;32:452–459. doi:10.3928/1081597X-20160428-07 [CrossRef]
- Gyöngyössy B, Jirak P, Schönherr U. Rotational stability and patient satisfaction after implantation of a new toric IOL. Eur J Ophthalmol. 2016;26:321–327. doi:10.5301/ejo.5000696 [CrossRef]
- Lubinski W, Kazmierczak B, Gronkowska-Serafin J, Podboraczynska-Jodko K. Clinical outcomes after uncomplicated cataract surgery with implantation of the Tecnis toric intraocular lens. J Ophthalmol. 2016;2016:3257217. doi:10.1155/2016/3257217 [CrossRef]
- Miyake T, Kamiya K, Amano R, et al. Long-term clinical outcomes of toric intraocular lens implantation in cataract cases with preexisting astigmatism. J Cataract Refract Surg. 2014;40:1654–1660. doi:10.1016/j.jcrs.2014.01.044 [CrossRef]
- Hirnschall N, Maedel S, Weber M, Findl O. Rotational stability of a single-piece toric acrylic intraocular lens: a pilot study. Am J Ophthalmol. 2014;157:405–411. doi:10.1016/j.ajo.2013.09.032 [CrossRef]
- Yang SW, Lee JH, Lim SA, Chung SH. Comparison of the clinical outcomes of two types of toric intraocular lens. J Korean Ophthalmol Soc. 2016;57:200–207. doi:10.3341/jkos.2016.57.2.200 [CrossRef]
- 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. doi:10.1007/s10384-011-0097-0 [CrossRef]
- Sanders DR, Sarver EJ, Cooke DL. Accuracy and precision of a new system for measuring toric intraocular lens axis rotation. J Cataract Refract Surg. 2013;39:1190–1195. doi:10.1016/j.jcrs.2013.06.006 [CrossRef]
Recent Studies Investigating Toric IOLs and the Results of Mean Absolute Rotation Values and Range Over Specific Time Periods
|Study||Toric IOL||Mean Absolute Rotation (°)||Range (°)||Time Period (Mo)|
|Ferreira et al.32||AcrySof IQ Toric||4.92 ± 4.10||Not stated||Not stated|
|Tecnis Toric Aspheric||4.31 ± 4.59|
|Gyöngyössy et al.33||Torica-aA||1.99 ± 1.88 (24 h to 6 mo)||0.10 to 7.40||0.03 to 18|
|0.84 ± 0.82 (6 mo to 1.5 y)||0.00 to 3.60|
|1.81 ± 1.87 (24 h to 1.5 y)||0.00 to 7.20|
|Lubinski et al.34||Precizion Toric 565||1.98 ± 1.78||0.70 to 2.29||4|
|Miyake et al.35||Torica-aA||1.99 ± 1.88||0.10 to 0.74||6|
|Hirnschall et al.36||Tecnis Toric ZCT||1.10 ± 2.40||0.00 to 8.00||6|
|Yang et al.37||AcrySof IQ Toric||2.20 ± 6.00 (1 wk to 3 mo)||Not stated||24|
|1.90 ± 2.30 (3 to 12 mo)|
|1.00 ± 1.20 (12 to 24 mo)|
|Watanabe et al.38||Tecnis Toric ZCT||2.20 ± 3.10||Not stated||3|
|Sanders et al.39||Tecnis Toric ZCT||3.20 ± 2.20||0.00 to 8.00||3|
|Zeiss AT TORBI||2.40 ± 2.00|
|Waltz et al.16||Tecnis ZCT 150||1.79 ± 2.12 (1 to 3 mo)||Not stated||3 to 6|
|1.89 ± 2.27 (3 to 6 mo)|