TECHNIQUE

Simple technique to measure toric intraocular lens alignment and stability using a smartphone Joshua C. Teichman, MD, MPH, FRCSC, Kashif Baig, MD, MBA, FRCSC, Iqbal Ike K. Ahmed, MD, FRCSC

Toric intraocular lenses (IOLs) are commonly implanted to correct corneal astigmatism at the time of cataract surgery. Their use requires preoperative calculation of the axis of implantation and postoperative measurement to determine whether the IOL has been implanted with the proper orientation. Moreover, toric IOL alignment stability over time is important for the patient and for the longitudinal evaluation of toric IOLs. We present a simple, inexpensive, and precise method to measure the toric IOL axis using a camera-enabled cellular phone (iPhone 5S) and computer software (ImageJ). Financial Disclosure: Dr. Ahmed is a consultant to Alcon Laboratories, Inc., and Abbott Medical Optics, Inc. No other author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2014; -:-–- Q 2014 ASCRS and ESCRS

As technology advances, the expected outcomes of cataract surgery patients continue to evolve. Most patients now expect spectacle independence after cataract surgery. Approximately 20% to 30% of patients have corneal astigmatism of 1.25 diopters (D) or higher prior to cataract surgery and correcting only the spherical component of the refractive error is becoming a thing of the past.1 One of the most frequent methods of correcting corneal astigmatism perioperatively is by implanting a toric intraocular lens (IOL). With the advent of toric multifocal IOLs, toric IOLs are being implanted with increasing frequency. A great deal of attention

Submitted: February 14, 2014. Final revision submitted: April 9, 2014. Accepted: April 13, 2014. From the Department of Ophthalmology (Teichman, Baig), University of Ottawa, Ottawa, Ontario, the Department of Ophthalmology and Vision Sciences (Ahmed), University of Toronto, Toronto, Trillium Health Partners (Ahmed), and Credit Valley EyeCare (Ahmed), Mississauga, Ontario, Canada. Corresponding author: Iqbal Ike K. Ahmed, MD, FRCSC, Credit Valley EyeCare, 3200 Erin Mills Parkway, Unit 1, Mississauga, Ontario L5L 1W8, Canada. E-mail: [email protected]. Q 2014 ASCRS and ESCRS Published by Elsevier Inc.

has been paid to preoperative and perioperative marking for toric IOL implantation, as well as to the postoperative measurement of IOL alignment and alignment stability over time. The postoperative alignment measurement is critical to determine whether the IOL has been placed in the proper position, whether any change in vision is attributable to IOL positioning, and whether rotational stability is achieved. This evaluation is important for the patient and for assessing future generations of toric IOLs. With newer toric IOLs that correct high degrees of astigmatism, proper alignment is increasingly important. Various techniques have been described to measure postoperative IOL alignment, including postoperative slitlamp examination using the rotating slit, various methods of digital overlay, vector analysis using the residual refraction and keratometry values, anterior segment optical coherence tomography, and wavefront aberrometry.1–5 The classic technique for measuring the IOL axis using the slitlamp is to dilate the pupil and rotate the slit beam until it coincides with the IOL markings. This technique may be complicated by not being able to properly align the beam with both sets of markings, causing an inaccurate reading. Moreover, in masked studies, this technique may be difficult to http://dx.doi.org/10.1016/j.jcrs.2014.09.029 0886-3350

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TECHNIQUE: MEASURING TORIC IOL ALIGNMENT USING A SMARTPHONE

Figure 1. Toric IOL in retroillumination, photographed using an iPhone.

use. As such, anterior segment photography may play an important role in identifying the IOL axis in an objective and masked fashion. This will become more important as new IOLs are designed and require evaluation. Slitlamp photography can be difficult to obtain, is expensive, is not automatically leveled, and may not be feasible for many community ophthalmologists. Methods to use a camera phone for slitlamp photography have been described.6,7 Numerous adapters for affixing a camera-enabled cell phone to a slitlamp exist and are of varying quality and price. Our technique is optimized with the use of a slitlamp adapter. We present a technique for measuring postoperative toric IOL axis using a camera-enabled cellular phone and show how this may be aided by applications for both the phone and one’s computer. TECHNIQUE For the postoperative evaluation, the patient is given mydriatic drops to achieve good pupil dilation. The patient is placed at the slitlamp biomicroscope, and proper head positioning including lack of head tilt is emphasized. The IOL is examined using retroillumination (Figure 1). An adapter is used to mount the camera–phone onto the slitlamp. A camera-enabled cellular phone (iPhone 5S, Apple, Inc.) is used to capture the photograph.

Figure 2. Screenshot of iPhone running Camera Awesome application with the level displayed on screen. Inset: Higher magnification view of level showing a nonlevel phone position. This box is not displayed on the phone’s screen.

If one were to use the factory-installed camera application on the iPhone, a high-quality picture could be captured. However, there is no way to determine whether the phone was level when the photograph was taken and any subsequent measurements would be inaccurate. With this in mind, a photography application that concurrently uses the iPhone’s internal accelerometer and displays a level is used (Camera Awesome, Smugmug, Inc.). In Figure 2, which is a screenshot of the application in use, the iPhone was not level; this is highlighted in the inset, which is not part of the original screenshot. When a photograph is captured, the level is not displayed on the recorded image. Therefore, care is taken to capture the image only while the camera– phone is level. Computer software (ImageJA) is then used to analyze the image. With this software, the photograph of interest is imported. A line is drawn between the IOL markings on opposite sides of the optic. If the phone is level when

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TECHNIQUE: MEASURING TORIC IOL ALIGNMENT USING A SMARTPHONE

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Figure 4. Screenshot of iPhone running Goniotrans with digital overlay of axes after importing a photograph of a toric IOL seen in retroillumination.

Figure 3. Screenshot of computer display running ImageJ with a level image of a toric IOL in retroillumination. An axis line is drawn, and the axis is read from the display above (blue oval).

image was captured, the IOL axis can be read directly from the screen without further processing (Figure 3). RESULTS The technique of measuring the postoperative IOL axis has been used for more than 1 year. The results have been reproducible, and the image-capture technique is simple, fast, and cost effective. The use of a slitlamp adapter increases the ease of the technique and is highly recommended. However, to demonstrate the simplicity even without additional hardware, the photographs shown were taken without the aid of an adapter. DISCUSSION As cataract surgery evolves, so do the expectations of our patients. Spectacle independence is becoming the new benchmark for successful cataract surgery, and for the 20% to 30% of the population with corneal cylinder of 1.25 D or more, astigmatism correction is required. Toric IOLs have gained popularity and are considered by

many to be one of the simplest forms of advanced technology IOLs. After implantation of a toric IOL, measurement of the axis is imperative to explain unforeseen patient outcomes and to continue to monitor our surgical techniques, as a pattern might emerge. Moreover, both short-term and long-term rotational stability will determine which toric IOLs are best for our patients and will also be one of the outcome measures in studies of the next generation of toric IOLs. Measurement of IOL alignment can be performed in a variety of manners; however, the simplest, cheapest, quickest, and most accurate will no doubt be the most frequently used method. We have described our preferred technique for postoperative IOL alignment measurement. We think it is also prudent to mention various methods that we have tried so the reader will be aware of some of the issues we found when not using this technique. With any technique (but not using a slitlamp adapter), we suggest not placing the camera directly up to the ocular but keeping a small distance between the phone and the ocular, as picture quality is improved with this configuration. Moreover, since the phone is now freely mobile, as it is not resting against the ocular, we recommend using both hands to steady the phone and often use an outstretched finger to rest on one of the oculars to aid in this. We found that the easiest method to accomplish this is to rest the phone’s camera close to the center of the ocular, which will produce only a small image on the screen and then move slowly backward away from the ocular keeping the expanding image central on the phone’s screen. The camera of the phone should be directed properly, which means aligned horizontally, vertically, and rotationally, as well as without tilt in the horizontal and vertical axes.

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TECHNIQUE: MEASURING TORIC IOL ALIGNMENT USING A SMARTPHONE

Because this can be difficult, we recommend using a slitlamp adapter. Image analysis can be performed using a variety of methods. One free method that we have used is the iPhone application Goniotrans (Eventos Medicos y Sociales, S.L.), which overlays marked axes over any picture (Figure 4). A version of this application is also available for Windows computers. Examining Figure 4, it is evident that the axis markings fall between 80 degrees and 90 degrees, approximately at 81 to 82 degrees. The Goniotrans technique requires careful centration of the overlay or erroneous results may occur. Thus, although this method can be used, it may be inaccurate as there remains subjectivity. A similar iPhone application, iMeasure Pro (iCoder), allows a protractor to be displayed on the iPhone screen while photographs are captured and are retained on the images. We found that the 360-degree protractor was the most accurate technique when we used this application; however, the alignment was not completely accurate and required subjective analysis. Another iPhone application, Angle Meter,B approaches the problem differently. Using this application, the iPhone is physically rotated to align with the axis markings and the angle is read from the iPhone screen. Without a slitlamp adapter, this method can be very difficult; even with an adapter, as the slitlamp ocular and the IOL may not fall in the same plane in 3-dimensional space, an inaccurate measurement may be obtained. For these reasons, we recommend using ImageJA for image analysis. The technique of simply drawing a line adjoining the IOL markings on a level photograph using ImageJ is accomplished in seconds and results in accurate measurement of an IOL axis. It is our preferred technique because of the ease of use and time efficiency. Postoperative vector analysis is a method to determine the IOL axis based on mathematical principles. It may be quite accurate, although for some it may be daunting or time consuming. Wavefront aberrometry is an objective method to measure the IOL axis; however, additional expensive equipment is required and may not be available to many ophthalmologists outside the refractive surgery arena. The technique we have described is a simple, inexpensive, and precise method to obtain level slitlamp photographs, which may be masked, for use in calculating toric IOL position. This method has been very helpful in the clinical setting and may be useful to those implanting toric IOLs in the community and the academic setting.

WHAT WAS KNOWN  Postoperative measurement of the toric IOL axis is crucial to assess patient and surgeon outcomes, as well as to monitor IOL rotational stability over time.  Numerous methods exist to measure toric IOL alignment, each with specific advantages and disadvantages. WHAT THIS PAPER ADDS  The current paper presents a simple, inexpensive, rapid, and precise method for measuring toric IOL axis that can be performed in a masked fashion using equipment readily available to the ophthalmologist. REFERENCES 1. Visser N, Bauer NJ, Nuijts RM. Toric intraocular lenses: historical overview, patient selection, IOL calculation, surgical techniques, clinical outcomes, and complications. J Cataract Refract Surg 2013; 39:624–637 2. Alpins NA, Goggin M. Practical astigmatism analysis for refractive outcomes in cataract and refractive surgery. Surv Ophthalmol 2004; 49:109–122 3. Watanabe K, Negishi K, Torii H, Saiki M, Dogru M, Tsubota K. 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 4. Nguyen TM, Miller KM. Digital overlay technique for documenting toric intraocular lens axis orientation. J Cataract Refract Surg 2000; 26:1496–1504 5. Shah GD, Praveen MR, Vasavada AR, Rampal NV, Vasavada VA, Asnani PK, Pandita D. Software-based assessment of postoperative rotation of toric intraocular lens. J Cataract Refract Surg 2009; 35:413–418 6. Barsam A, Bhogal M, Morris S, Little B. Anterior segment slitlamp photography using the iPhone. J Cataract Refract Surg 2010; 36:1240–1241 7. Teichman JC, Sher JH, Ahmed II. From iPhone to eyePhone: a technique for photo documentation [letter]. Can J Ophthalmol 2011; 46:284–286

OTHER CITED MATERIAL A. Rasband W. ImageJ; Image Processing and Analysis in Java. Research Services Branch, National Institute of Mental Health, Bethesda, Maryland, USA. Available at: http://rsb.info.nih.gov/ij/ . Accessed July 3, 2014 B. Jeon J. Angle Meter (Free). Available at: https://itunes.apple. com/us/app/angle-meter-free/id436775826?mtZ8. Accessed July 3, 2014

J CATARACT REFRACT SURG - VOL -, - 2014

First author: Joshua C. Teichman, MD, MPH, FRCSC Department of Ophthalmology, University of Ottawa, Ottawa, Ontario, Canada

Simple technique to measure toric intraocular lens alignment and stability using a smartphone.

Toric intraocular lenses (IOLs) are commonly implanted to correct corneal astigmatism at the time of cataract surgery. Their use requires preoperative...
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