Digital overlay technique for documenting toric intraocular lens axis orientation

Deviation from the planned axis of three toric intraocular lenses

In this study, we retrospectively evaluated the deviation from the planned axis of 3 Toric intraocular lenses (TIOL). Included in the study 190 eyes, operated by two surgeons using two different manual marking techniques. The patients were implanted with either AcrySof IQ Toric SN6AT (Alcon) (n = 90), POD FT (PhysIOL) (n = 50), or TECNIS Symfony Toric (J&J) (n = 50). At least 1 month postoperatively, the IOL was photographed, and the axis was measured using a designed software. The difference between the planned and actual axis was defined as axis deviation. The effect of IOL type, astigmatism direction, and marking techniques on the average degree and direction of the IOL deviation were evaluated and compared. There was no significant difference in the average deviation between the IOLs (TECNIS Symfony: 4.03° ± 4.34, POD FT: 3.52° ± 3.38, and SN6AT: 4.24° ± 4.10), and its direction (55.8%, 39.0%, and 56.6% clockwise (CW) deviation, respectively). With the rule, astigmatism had significantly more CW deviation compared with against the rule and oblique astigmatism (64.3%, 43.8%, and 41.7%, respectively, P = 0.027), but the average deviation was similar. The marking techniques did not influence the degree or direction of the deviation.

Evaluation of postoperative toric intraocular lens alignment with anterior segment optical coherence tomography

We describe the use of a simple tool to evaluate the postoperative alignment of toric intraocular lenses (IOLs). The entire anterior segment is scanned using anterior segment optical coherence tomography and analyzed with an internal dedicated tool. A topographic map is displayed along with an anterior segment image, including a linear axis marker centered on the corneal apex. The marker can be rotated until it is aligned with the line connecting the IOL marking dots, precisely reproducing the IOL astigmatic axis, which is measured in angle degrees. The value of the IOL astigmatic axis is compared with the value of the astigmatic axis shown in real time on the same screen in the topographic map. Evaluating the alignment of a toric IOL axis simultaneously with the topographic astigmatic axis eliminates the potential errors that result from head tilting and strictly correlates with the astigmatic correction achieved.

Accuracy of toric intraocular lens implantation using automated vs manual marking

BACKGROUND

Accurate alignment of toric intraocular lens (TIOL) to steep corneal astigmatic axis is important to achieve effective postoperative results. The authors compare the accuracy of astigmatism correction using automated and manual marking in TIOL implantation during cataract surgery.

METHODS

One hundred thirty-two eyes with nuclear density from Grade 2 to 4 were randomly subdivided into 2 groups (automated and manual marking). All patients underwent manual marking and the steep axis was compared to SensoMotoric Instruments (SMI). After phacoemulsification, 62 patients underwent toric IOL implantation using the SMI and 70 patients underwent toric IOL implantation using manual marking. Intraoperative measurement was the steep axis difference. Clinical measurements included preoperative and postoperative best corrected visual acuity (BCVA), and TIOL axis.

RESULTS

The intraoperative steep axis difference between SMI and manual marking was 7.86 ± 6.4 degrees. The difference between the preoperative steep axis and the postoperative TIOL axis using SMI (3.63 ± 1.12 degrees) was significantly lower than that using manual marking (8.29 ± 2.23 degrees) (P < 0.05).

CONCLUSIONS

The steep axis measurements may be different when using SMI vs. manual marking. The SMI is more accurate than manual marking for TIOL implantation during cataract surgery.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN12294725 , Retrospectively registered, on 20 July 2018.

A comparison of three different corneal marking methods used to determine cyclotorsion in the horizontal meridian

During toric intraocular lens (IOL) implantation, surgeons must take particular care to ensure that inaccurate preoperative measurement and intraoperative misalignment do not cause unexpected postoperative residual astigmatism. This retrospective, comparative case series study aimed to analyze the rotational deviation, or cyclotorsion, of three corneal marking methods: VERION digital marker (VDM; reference), horizontal slit beam marking (HSBM), and subjective direct visual marking (SDVM) on the table (using a bevel knife tip). Subjects included 81 eyes of 61 patients (mean age: 65.70±13.14 years; range: 32–91 years) undergoing scheduled cataract surgery. A preoperative reference image was taken of each eye. Subsequently, a slit lamp with the light beam turned to the horizontal meridian was used to align the seated patient’s head, and two reference marks were placed at the 3- and 9-o’clock positions of the corneal limbus using a 27-gauge needle and marking pen (HSBM). Upon transfer to the surgical table, the VDM was used to display a real-time dial scale on the patient’s eye, with the entrance of the temporal clear corneal incision (CCI) at 0° (horizontal meridian). Simultaneously, a bevel knife tip was used to create a marker based on the surgeon’s visual determination of the temporal 0° point (SDVM). We used the VDM to quantitatively evaluate the accuracy of axis alignment via deviation from the horizontal reference meridian. Compared with the reference meridian, the SDVM (−3.46°±7.32°, range: −18° to 13°) exhibited greater average relative cyclotorsion versus the HSBM (0.41°±4.92°, range: −10° to 10°). Furthermore, the mean average misalignment was significantly less in the HSBM group versus the SDVM group (t=4.179, P<0.001). The VDM is likely a reliable marking method, similar to the HSBM. In contrast, the SDVM is not entirely reliable. The VDM usage may prevent inaccurate preoperative manual marking during toric IOL implantation.

Influence of the overall intraocular lens diameter on rotational stability

PURPOSE

To evaluate the rotational stability of two intraocular lenses (IOLs) of similar design and material but with a difference of 1 mm in overall length.

METHODS

In this prospective study patients with age-related cataract were included. An IOL with an overall diameter of 12 mm (ACR6 = small-diameter IOL) was compared to an IOL with an overall diameter of 13 mm (IDEA 613 XC = large-diameter IOL).

RESULTS

In total, 60 patients were included in this study. Absolute rotation in the small- and large-diameter groups was 4.4° (SD: 4.0; range: 0.3-17.8) and 3.0° (SD: 2.4; range: 0.1-7.8), respectively. The differences between the two IOLs were not found to be statistically significant.

CONCLUSION

The effect of the overall length of an IOL appears to have little impact on early rotation after cataract surgery.

Accuracy and precision of a new system for measuring toric intraocular lens axis rotation

We determined the accuracy and precision of a new system for measuring postoperative toric intraocular lens (IOL) axis rotation. The system performs high-resolution retroillumination photography to identify toric IOL axis markings and then takes a photograph of the iris and conjunctival/scleral vessels. Built-in software measures the toric axis to within 0.2 degree. If performed twice on the same eye, the system will correct the 2 toric axis measurements for cyclorotation/head tilt using iris/vessel registration. Testing in 37 eyes showed that using iris/vessel registration correction reduced the mean absolute toric IOL axis rotation by a factor of 4.5. We conclude that this system seems to be both accurate and precise for measuring postoperative toric IOL axis rotation.

Rotational stability of a single-piece toric acrylic intraocular lens: a pilot study

PURPOSE

To evaluate the visual performance and rotational stability of the Tecnis Toric 1-piece intraocular lens (IOL) during the first 3 postoperative months.

DESIGN

Prospective, single-center study.

METHODS

In this study, patients with age-related cataract and corneal astigmatism of 1.0 to 3.0 diopters measured with the IOLMaster 500 (Carl Zeiss Meditec AG) were included. Before surgery, rotating Scheimpflug scans (Pentacam HR; Oculus) were performed and the cornea was marked in the sitting position at the slit lamp. Patients received a single-piece toric hydrophobic acrylic IOL (Tecnis Toric; AMO). Immediately and 3 months after surgery, retroillumination photographs were obtained to assess the rotational stability of the IOL. Additionally, Autorefraction (Topcon), subjective refraction, uncorrected and distance-corrected visual acuity, keratometry, and Scheimpflug and ocular wavefront (WASCA, Carl Zeiss Meditec AG) measurements were performed at the 3-month follow-up.

RESULTS

Thirty eyes of 30 patients were included in this study. Mean absolute difference between the IOL axis at the 3-month and 1-hour follow-up was 2.7 degrees (standard deviation, 3.0 degrees). The IOL rotation was less than 3 degrees and less than 6 degrees in 62% and 95% of all cases, respectively.

CONCLUSIONS

The Tecnis Toric 1-piece IOL is rotationally stable and shows excellent capsule bag performance and refractive outcomes.

Simple and accurate alignment of toric intraocular lenses and evaluation of their rotation errors using anterior segment optical coherence tomography

PURPOSE

To describe a new method of alignment of toric intraocular lenses (IOLs) and evaluation of their rotation errors using anterior segment optical coherence tomography (AS-OCT).

METHODS

Twenty-nine eyes of 22 patients who had cataract extraction and implantation of an acrylic toric IOL were included. The new AS-OCT method was used for the alignment of toric IOLs and evaluation of their rotation errors. These rotation errors were evaluated and compared with those measured using the internal map of a wavefront aberrometer.

RESULTS

The mean rotation error ± standard deviation (SD) of the toric IOLs evaluated by AS-OCT was 3.2 ± 2.2° and 3.2 ± 2.4° at 1 week and 1 month after surgery, respectively. The mean difference in the reference axis between the visits was 1.8 ± 2.1°. The mean difference between the rotation errors of the alignment axes measured by AS-OCT and the internal map was 2.5 ± 1.9° (P = 0.037).

CONCLUSION

The current method is clinically useful not only for the accurate alignment of toric IOLs but also for evaluating their rotation errors.

Clinical and experimental validation of a slit lamp modification to measure toric lens position

AIM

A simple novel slit lamp beam angular scale modification is described to allow more accurate measurement of toric contact and intraocular lens position.

METHODS

The modified slit lamp measuring technique was validated in both an experimental and a clinical setting, with two independent observers. The device was tested against a known reference source, and intraobserver variability in a clinical setting measuring toric intraocular lens (IOL) position was ascertained.

RESULTS

In the experimental setting 80 paired observations were analysed. Mean variance was 0.19° (95% CI 0.01-0.37), with a typical measurement error of 0.49°. Intraobserver variation had variance of -0.03° (95% CI -0.2 to 0.15) with a typical error of 0.47°. Clinical assessment of toric IOL position was made in 21 eyes. For this group, intraobserver variation had variance of -0.1° (95% CI -0.281 to 0.62) with a typical error of 1.36°. Intraclass correlation coefficient for all measures was 1.0.

CONCLUSION

This simple technique has sufficient precision to be valuable in the clinical setting where photographic techniques may not be available or practical.

Acrylic toric intraocular lens implantation: a single center experience concerning clinical outcomes and postoperative rotation

Purpose:

To present clinical results of toric intraocular lens (IOL) implantation for preexisting astigmatism correction and determine the time of any postoperative rotation.

Patients and methods:

Twenty-nine eyes of 19 patients underwent uncomplicated phacoemulsification and were implanted with an Acrysof ^© toric IOL. Uncorrected visual acuity, residual astigmatism, and postoperative rotation of the IOL were estimated one and six months after the operation.

Results:

Uncorrected visual acuity was ≥0.5 in 26 of 29 eyes (89.7%) and ≥0.8 in 19 of 29 patients (65.5%). The mean toric IOL axis rotation was 2.2 ± 1.5° (range 0.6–7.8°) one month postoperation and 2.7 ± 1.5° (range 0.9–8.4°) six months postoperation.

Conclusion:

Implantation of one-piece hydrophobic acrylic toric IOLs appears to have acceptable stability, which encourages visual outcome and emerges as an attractive alternative for correction of refractive astigmatism.

Long-term Staar toric intraocular lens rotational stability

PURPOSE

To evaluate the long-term rotational stability of Staar toric intraocular lens (IOL) implants from two weeks after cataract surgery until two weeks after laser posterior capsulotomy.

DESIGN

Retrospective interventional case series.

METHODS

One hundred and fifteen eyes of 72 patients were implanted with Staar toric IOL models AA4203TF and AA4203TL (Staar Surgical Co, Monrovia, California, USA) between November 1998 and November 2004. Forty-two (36.5%) of the 115 eyes underwent laser capsulotomy because of clinically significant posterior capsule opacification. Slit-lamp retroillumination photographs were obtained in 25 eyes two weeks after cataract surgery and again two weeks after capsulotomy to document IOL axis alignment.

RESULTS

The mean difference in axis alignment before and after posterior capsulotomy was 1.36 degrees. In no case did the axis change more than 5 degrees. This amount is within the expected range of measurement error using a slit-lamp photographic technique for axis measurement.

CONCLUSION

There are no long-term changes in Staar toric IOL axis orientation beyond the two-week postoperative time point after cataract surgery. The rotational stability extends through laser posterior capsulotomy.

Calculating the power of toric phakic intraocular lenses

BACKGROUND AND PURPOSE

A toric phakic intraocular lens (IOL) implanted in the anterior or posterior chamber of the eye has the potential to correct high or excessive ametropia and astigmatism with high predictability of the postoperative refraction and preservation of phakic accommodation. The calculation of spherical phakic lenses has been described previously, but a formalism for estimating the power of toric phakic lenses has not yet been published. The purpose of this study is to describe a mathematical strategy for calculating toric phakic IOLs.

METHODS

The method presented in this paper is based on vergence transformation in the paraxial Gaussian space. Parameters used for the calculations are the spherocylindrical spectacle refraction before implantation, corneal power (sphere and astigmatism) and (spherocylindrical) target refraction, together with the vertex distance and the predicted position of the phakic IOL. The lens power is determined as the difference in vergences between the spectacle-corrected eye and the uncorrected eye at the reference plane of the predicted lens position. The axes of the preoperative refraction, the target refraction and the corneal astigmatism are at random (not necessarily aligned).

RESULTS

The method was applied to two clinical examples. In example 1 we calculate the power of a phakic lens for the simple case, when the target refraction is plano and the axis of the preoperative refraction is aligned to the axis of the corneal astigmatism. In example 2, the cylindrical axis of the preoperative refraction is not aligned to the corneal astigmatism and the target refraction is spherocylindrical (and the axis of the target refraction is not aligned to the preoperative refractive cylinder or the corneal astigmatism). The calculations for both examples are described step-by-step and illustrated in a table.

CONCLUSIONS

The calculation scheme can be generalized to an unlimited number of crossed cylinders in the optical pathway. Based on paraxial raytracing, the spherical and cylindrical power as well as the orientation of the cylinder are determined from the preoperative refraction (including vertex distance), the corneal power, the intended target refraction (including vertex distance) and the predicted position of the phakic lens implant provided by the lens manufacturer. This calculation scheme can be easily implemented in a simple computer program (i.e. in Microsoft excel or matlab).

Torische Intraokularlinsen und Astigmatismuskorrektur

Toric intraocular lenses (tIOLs) have the potential to correct corneal astigmatism. The purpose of this review paper is: 1. to describe the biometric, keratometric and topographic conditions for implantion of tIOLs, 2. to highlight the advantages and disadvantages of tIOLs, 3. to define indications for and contraindications to tIOL implantation, 4. to provide clinical recommendations for the implantation of toric lenses, and 5. to report the specifications of all tIOLs that are currently available commercially.

Impact of decentration of astigmatic intra-ocular lenses on the residual refraction after cataract surgery*

PURPOSE

The purpose of this study is to assess the impact of decentration of astigmatic intra-ocular lenses on the residual refraction after cataract surgery, using a computing scheme with 5 x 5 system matrices.

METHODS

Based on the definition of an optical system in the paraxial Gaussian space containing astigmatic surfaces without restrictions to coaxiality, we derived a method (using 5 x 5 refraction and translation matrices) for calculating the residual refraction and the compensating prism in the spectacle plane after decentred implantation of thin and thick astigmatic intra-ocular lenses. The 'optical system eye' may contain astigmatic refractive surfaces with their axes at random.

RESULTS

The capabilities of this computing scheme are demonstrated with two examples. In example 1 we calculate the residual refraction of a decentred 'thin astigmatic lens' for compensation of corneal astigmatism to achieve a spherical target refraction. In example 2 we compute the residual refraction after implantation of a 'thick astigmatic lens', where the spherical and cylindrical power as well as the implantation axis of the lens do not fully match the pre-operative recommendations and the lens is decentred relative to the optical axis. For both examples, we derive the residual prismatic effect in the spectacle plane and the lateral displacement of a ray exiting the spectacle correction when starting coaxially at the retina.

CONCLUSIONS

We have presented an en bloc matrix-based strategy for the calculation of the residual spherocylindrical refraction at the spectacle plane after implantation of a decentred thin or thick astigmatic intra-ocular lens without restrictions to coaxiality. The resulting system matrix is written as a product of 5 x 5 refraction and translation matrices.

Evaluating the eye's rotational stability during standard photography

PURPOSE

To evaluate the rotational stability of the eye during standard photography and determine its effect on the measurement of toric intraocular lens (IOL) orientation.

SETTING

Department of Ophthalmology, University Erlangen-Nuremberg, Erlangen, Germany.

METHODS

The rotational stability of the eye was evaluated using standard photographs taken with a telecentric fundus camera (Zeiss). Two sets of fundus images were taken at least 6 months apart in 400 eyes of 200 patients. The axial position of the eye was determined using 2 characteristic markers of the fundus. The angle between the 2 images (autorotation angle) was measured in each eye.

RESULTS

The mean absolute autorotation was 2.3 degrees +/- 1.7 (SD) (range 0 to 11.5 degrees). Nine percent of eyes did not rotate. The rotation was less than 3 degrees in 55% of eyes and was 3 degrees or greater in 36% of eyes. Eyes of patients younger than 50 years rotated less than eyes in older patients (mean 2.2 +/- 1.5 degrees and 2.5 +/- 1.8 degrees, respectively) (P=.04). A visual acuity of 20/20 or better (P=.02) and a refractive cylinder of less than 1.75 diopters (P=.01) were correlated with smaller amounts of autorotation. Potential causes of artificial eye rotation induced by the photographic technique included camera adaptation (3-degree intrinsic error), slide mounting (<1 degree), slide projection (<0.5 degree), marking of characteristic fundus details (<1 degree), and head inclination.

CONCLUSIONS

Cyclorotation of the eye during standard photography may lead to overestimation or underestimation of the presumed spontaneous rotation of an implanted toric IOL. Results show that 11.5 degrees of toric IOL rotation would lead to residual astigmatism that is 40% of the initial astigmatic power and 3 degrees, 10% of the initial power. Digital imaging may reduce the intrinsic errors of standard photography.

Matrix-based calculation scheme for toric intraocular lenses

BACKGROUND AND PURPOSE

While a number of intraocular lens power prediction formulas are well established for determination of spherical lenses, no common strategy is published for the computation of toric intraocular lenses. The purpose of this study is to describe a paraxial computing scheme using 4 x 4 system matrices to describe the 'optical system eye' containing astigmatic refractive surfaces with their axes at random.

METHODS

Based on the definition of a centred optical system in the paraxial Gaussian space containing astigmatic surfaces using 4 x 4 refraction and translation matrices, we derived a methodology for calculating the refractive power of thin and thick toric intraocular lenses by solving a linear equation system. In a second step, we derived a methodology for prediction of the residual spectacle refraction after implantation of any toric lens implant with any orientation.

RESULTS

The capabilities of this computing scheme are demonstrated with three examples. In example 1 we calculate a 'thin toric lens' for compensation of a corneal astigmatism to achieve a spherical target refraction. In example 2 we compute a 'thick toric lens', which has to compensate for an oblique corneal astigmatism and rotate the spectacle cylinder to the 'against the rule' position to enhance near vision. In example 3 we predict the residual refraction at the corneal plane after implantation of a thick toric lens, when the cylinder of the lens implant is compensating the corneal cylinder in part and the axis of implantation is not fully aligned with the axis of the corneal astigmatism.

CONCLUSION

We present an en bloc matrix-based strategy for the calculation of thick or thin toric intraocular lenses, with the flexibility of crossing an unlimited number of cylinders with restrictions to paraxial optics. The resulting system matrix S is written as a product of 4 x 4 refraction and translation matrices. Residual refraction at the corneal (contact lens) or spectacle plane can be derived by inverting the order of matrices for calculation of the system matrix.

Compensation of aniseikonia with toric intraocular lenses and spherocylindrical spectacles

BACKGROUND AND PURPOSE

Magnification disparity between the two eyes (aniseikonia) is one of the major unresolved problems in modern cataract surgery, potentially degrading binocular visual function or causing diplopia. The purpose of this study is to describe a paraxial computing scheme using 4x4 system matrices to simulate a corrected pseudophakic 'optical system eye' with a meridional magnification that matches the magnification of a given contralateral eye.

METHODS

Based on the definition of a centred optical system in the paraxial Gaussian space containing astigmatic surfaces using 4x4 refraction and translation matrices, we derived a methodology for calculating the refractive power and axis of toric intraocular lenses and spherocylindrical spectacle corrections for (i) fully correcting the optical system eye and (ii) realizing an arbitrary meridional magnification by solving a linear equation system.

RESULTS

The capabilities of this computing scheme are demonstrated with two examples. In example 1 we calculate a toric lens and a spherocylindrical spectacle correction for compensation of a corneal astigmatism to realize a predefined iso-meridional magnification. In example 2 we first determine the meridional magnification of the contralateral eye, which has been treated with cataract surgery and toric lens implantation, and then we compute the appropriate combination of a fully correcting toric lens and spherocylindrical spectacle refraction, which exactly matches the meridional magnification of the contralateral eye.

CONCLUSION

We presented an en bloc matrix based strategy for the calculation of an optical system eye containing an astigmatic cornea, a toric lens implant and a spherocylindrical spectacle correction, where the toric lens and the spherocylindrical spectacle correction are determined to fully correct the system and to realize an arbitrary meridional magnification i.e. to eliminate aniseikonia.

Computerized calculation scheme for toric intraocular lenses

BACKGROUND AND PURPOSE

While a number of intraocular lens (IOL) power prediction formulae are well established for determination of spherical lenses, no common strategy has been published for the computation of toric IOLs. The purpose of this study is to describe a paraxial computing scheme for tracing an axial pencil of rays through the 'optical system eye' containing astigmatic refractive surfaces with their axes at random. The capabilities of this computing scheme are demonstrated with clinical examples.

METHODS

Based on a schematic model eye with spherocylindric surfaces, we use two alternative notations for description of vergences or prescriptions: (1) standard notation (refraction in both cardinal meridians and axis), and (2) component notation (spherical equivalent and cylindric component in 0 degrees and 45 degrees. Refractive surfaces are added to the vergence in component notation, whereas the transformation of the vergence through media is performed in the standard notation for both cardinal meridians. For calculation of the toric lens implant, a pencil of rays is traced through the spectacle and the cornea to the estimated lens position as well as backwards from the retina to the estimated lens position. For calculation of residual spectacle refraction, a pencil of rays is traced backwards from the retina through the toric lens implant and the cornea to the spectacle plane.

RESULTS

In example 1 we calculate a 'thin toric lens' for compensation of a corneal astigmatism to achieve a spherical target refraction. In example 2 we compute a 'thick toric lens', which has to compensate for an oblique corneal astigmatism and rotate the spectacle cylinder to the against the rule position to enhance near vision. In example 3 we estimate the residual refraction at the corneal plane after implantation of a thick toric lens, when the cylinder of the lens implant is compensating the corneal cylinder in part and the axis of implantation is not fully aligned with the axis of the corneal astigmatism.

CONCLUSION

This novel mathematical concept for computation of toric IOLs or prediction of the refractive outcome with a toric implant in place is a straightforward, computer-based approach, which may substitute for more or less empirical methods of determining toric IOL implants.

Correcting high astigmatism with piggyback toric intraocular lens implantation

An 86-year-old man presented for cataract surgery with corneal astigmatism of 5.12 diopters (D). After cataract extraction with small-incision techniques, 2 toric plate-haptic silicone intraocular lenses (IOLs) were implanted in the capsular bag, each with a 3.50 D cylinder add (2.30 D at the spectacle plane). Six weeks postoperatively, corneal astigmatism was 3.38 D at 70 degrees and refractive astigmatism was 1.00 D at 20 degrees. Uncorrected visual acuity was 20/40. No IOL rotation was observed. Implantation of piggybacked toric lenses may be a viable option for correcting moderate to high astigmatism.

Treating astigmatism at the time of cataract surgery

Correcting astigmatism at the time of cataract surgery can be accomplished either by incisional techniques, such as use of a cataract incision for flattening or astigmatic keratotomy, or by implanting a toric intraocular lens. Both methods can reduce mild to moderate astigmatism. For correcting larger amounts of astigmatism, a combination of techniques can produce greater correction. New methods of analyzing the change induced by surgery provide a more complete understanding of the astigmatic change.