Toric lens calculator alcon

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One of the key considerations is hydrophilic versus hydrophobic designs. Hydrophilic lenses go through a much smaller incision than hydrophobic lenses 1. However, an incision this size requires more specialised equipment, and the hassle-to-benefit ratio favours it being a hassle, in my view.

I advise new surgeons to make their incision size as small as they comfortably can. There is no longer a reason to use a 2.

The sweet spot of incision sizes is 2. It provides for a multitude of choices, including hydrophobic lenses. Hydrophilic lenses have had bad press in the past few years because of fears of opacification, especially if they are exposed to gases inside the eye.

In my experience of reviewing these IOLs over many years, I have not seen a single opaque lens, but I accept it does occur on rare occasions. I think the risks of hydrophilic lens use have been overstated. I avoid them in patients who may undergo procedures with gas in the future, such as an endothelial transplant, but in a standard eye it would not sway my decision. Certain hydrophilic lenses also have an advantage in terms of ease of rotation.

This benefits those who are learning because there is no need to worry about the direction of rotation to the targeted axis.

The extra time involved should not be a concern, though. This is better than having to schedule a second surgery to rotate a misplaced toric IOL. Another consideration is the cylinder steps that each manufacturer produces. My colleagues and I recently completed a study evaluating whether the step magnitude made any difference in around 1, implanted eyes with two surgeons using 0. We audited our results and found no significant difference between the two in terms of residual refractive error unpublished data.

This might seem counterintuitive because you would think that smaller steps yield better results. The key is to keep in mind that regardless of whether you are using 0. In the end, IOL selection will likely come down to familiarity with the platform.

There are no features of the major toric IOLs that make me feel that any one is significantly superior to the others. Whether you are used to a plate haptic or a C-loop haptic, stick with that selection for your early cases and then feel free to experiment once you have some experience.

Eventually you will choose based on the predictability of refractive results but, until that time, I urge you to try all the options and see what suits you best. There are a lot of third-party and manufacturer toric IOL calculators online. With very basic maths, anyone can calculate what spherical power an eye needs by simply knowing the shape of the front and the length of the eye.

Calculating a toric lens means calculating two lenses — one for each axis. This is still rather simple but people have put a lot of time and effort into refining the process by taking into account the expected lens position, anticipated tilt, posterior corneal astigmatism, etc. Each of the main lens manufacturers has a calculator, and those such as the Barrett Toric Calculator are also available.

When people are implanting a spherical lens, they will usually look at multiple formulas and decide on which formula suits the eye. With a toric calculator, you do not have this option unless you want to look at multiple calculators. Historically, toric calculators would use the anterior keratometry values and tell you which toric lens would suit a particular eye to give the best refractive outcome.

However, we then rediscovered that posterior corneal astigmatism has an impact on the precision of that calculation. Therefore, different ideas arose for how to incorporate the posterior cornea into the toric IOL calculation. He reported that, depending on the orientation of the anterior corneal astigmatism, you can adjust the cylinder power for that eye up or down.

The other nomogram was from Dr Michael G. Goggin: he adjusted the input instead of the output. He adjusted the keratometry values themselves, and his nomogram is available online at goggintoric.

I use this calculator because it is the only toric calculator that has prospective published data proving that it is effective. If you used one of those calculators and also added the Baylor or the GNAK, in principle you would over-adjust for the posterior cornea because you would adjust for it twice.

Now, you can simply use one of those calculators mentioned. What you will find is, when an adjustment is made for the posterior cornea in the calculation of the toric IOL, there is an adjustment made to the power of the cylinder that you are putting in, and you will also notice an adjustment to the axis of implantation. This means that when you take the posterior cornea into consideration as well as the anterior cornea, you are playing with the total corneal power.

It is simple vector mathematics that makes sense. Notably, the steep axis of the total cornea may be quite different from what you have measured on the anterior surface.

This will have the biggest impact for a toric lens to treat low-powered oblique astigmatism. A recent study revealed that when you are dealing with an eye with oblique anterior corneal astigmatism, there is no need to adjust the axis of toric IOL implantation from the steep axis of the anterior cornea.

It can be quite disconcerting to go against the recommendation of online calculators, so I recommend starting with simple with-the-rule or against-the-rule eyes. Refractive surprise after toric intraocular lens implantation: graph analysis. J Cataract Refract Surg. Alpins NA. A new method of analyzing vectors for changes in astigmatism. Astigmatism analysis by the Alpins method. By Graham D. Our ability to provide excellent unaided acuity after cataract surgery improved dramatically with the introduction of toric IOLs.

Nevertheless, despite accurate keratometry, precise alignment, and complex calculations, the refractive outcome after toric IOL implantation is not always predictable.

Choosing the correct toric IOL for patients is more challenging than choosing a spherical IOL power, as we have to consider the magnitude and axis of the toric cylinder required. In order to avoid unexpected astigmatic outcomes, we must consider which devices should be used to measure the cornea, how to interpret the measurements, which methods to use to predict the required cylinder, and which technique will most acccurately align the toric IOL axis.

Methods to predict the required cylinder. This phenomenon is known as Javal's rule and is thought to be due to the posterior cornea contributing, on average, 0. There are several toric IOL calculators available. This can be adjusted for the posterior cornea's contribution using the Baylor nomogram. The Holladay calculator uses ELP to calculate the corneal vector of the toric IOL, and it can be adjusted based on the Baylor nomogram or direct measurement of the posterior cornea.

The Barrett Toric Calculator. The calculator derives the posterior corneal curvature based on a theoretical model proposed to explain the behavior of the posterior cornea. The toric IOL cylinder power required to correct the corneal astigmatism—including posterior corneal astigmatism—is calculated from the predicted ELP using vector calculations for each eye.

In a study conducted at Ein-Tal Eye Center and awaiting publication in the Journal of Cataract and Refractive Surgery , the most accurate prediction of residual astigmatism was achieved with the Barrett Toric IOL calculator in combination with the Lenstar.

In a subsequent study I performed with my fellow Adi Abulafia, MD, in Perth, Australia, we analyzed 54 eyes implanted with toric IOLs, comparing pre- and postoperative Ks, the intended versus actual axis of alignment, and different calculators to identify the relative contribution of each of these factors to errors in predicted residual astigmatism.

The results showed that errors in estimating surgically induced astigmatism SIA adversely affect the predictability of toric IOL outcomes and that utilizing the centroid value for SIA offers significant improvement. Similarly, eliminating errors in axis alignment offers further improvement, but the effect is less significant. The most important benefit, however, that can be obtained in improving toric IOL outcomes comes from use of an improved calculator.

This formula recommends the required IOL power for lens exchange, piggyback IOLs, or the rotation of an existing toric IOL to correct for an unexpected refractive outcome. Techniques to acccurately align the toric IOL axis.

Although, clinically, the impact of misalignment appears to be less than not taking into account factors such as posterior corneal astigmatism, there are several techniques that can be considered to improve alignment. Today, we have sophisticated systems to help minimize errors in alignment of a toric IOL on the required axis. These include intraoperative determination of the axis with wavefront devices or image-guided systems.

I then use the toriCAM app to align the red reference axis indicator with the limbal marks, press the camera button, and capture an image. The images are stored in the photo album of my iPhone, and toriCAM records the reference axis, patient name, and date and time of the image.

I then set the desired toric axis on my marker and offset the reference axis accordingly. A custom toric marker specifically for the toriCAM app is available, allowing the surgeon to set the reference axis as indicated by the app independently from the toric axis recommended by the toric calculator.

Applying the inked marker then provides accurate marks with which the toric IOL can be aligned after insertion. Understanding the source of potential errors during measurement, prediction, and alignment—with careful attention to each step in the process—can minimize the likelihood of an unexpected astigmatic result.

By Mark S. Hansen, MD; John P. Berdahl, MD; and David R. Hardten, MD Available at www. The Toric Results Analyzer calculator was developed by Drs. Berdahl and Hardten as a tool for dealing with residual astigmatism following toric IOL implantation.

Residual astigmatism often remains after surgery, and this is confirmed by the fact that surgeons have used the Toric Results Analyzer for more than 20, IOL calculations over the past 2 years. This easy-to-use calculator helps surgeons determine if residual astigmatism following toric IOL implantation can be corrected by simply rotating the lens.

It also provides information that can be used to determine the ideal rotation of the lens to correct residual astigmatism and can provide information for an IOL exchange if a higher or lower toric power is needed. In cases in which rotation or exchange would not be useful, most surgeons opt for laser vision correction. The information required to use the calculator includes the patient's current refraction in plus or minus sphere , the intended IOL axis, and the toric lens information spherical power and cylinder power at corneal plane , including the current axis Figure 6.

After this information is entered, the calculator indicates the axis the lens should be rotated to in order to decrease the amount of astigmatism to an acceptable level Figure 7. If the predicted refraction after rotation is acceptable as the intended target, then rotating the lens can be attempted. If the expected refraction after rotating the lens would not be acceptable, then a lens exchange or laser vision correction can be considered.

It is important to get the axis measurement accurate. This can best be achieved at the slit lamp when the patient is dilated.

Align a slit beam with the axis of the toric lens marks.

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Toric lens calculator alcon	Novis C. The sweet spot of incision sizes is 2. Sci Rep. A amerigroup health care careers in contrast sensitivity as compared to a monofocal IOL may be experienced by some patients and may be more prevalent calvulator low lighting conditions. A new method of analyzing vectors for changes in astigmatism. My colleagues and I recently completed a study evaluating whether the step magnitude made any difference in around 1, implanted eyes with two surgeons using 0.
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Toric lens calculator alcon	In Click the following article 2 of this three-part series, I will provide tips on calculating toric IOL sphere and cylinder power, which can be a great concern to surgeons who use these lenses. As soon as the magnitude and axis of the cataract incision have been entered, a black arcuate trapezoid is shown at the limbus on the drawing Figure 9. Acknowledgements D. Notes Competing Interests The authors declare no competing interests. This calculation displays a mean K of In such cases, it is important to know what type of tIOL calculator is used for lens selection.
Health plus with amerigroup	Some others use a variable ratio centered at 1. J Cataract Refract Surg. Corresponding author. He adjusted the keratometry values themselves, and his nomogram is available online at goggintoric. Figure 1. By Jack T. These values were input into the Abbott calculator, calcjlator zero surgical astigmatism, and three toric lenses were recommended.
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