Optimizing Visual Results with the Crystalens

By Uday Devgan, MD, FACS, FRCS (Glasg)

Most of my cataract patients are young at heart, well-read, and interested in achieving sharp vision and spectacle freedom at a wide range of distances. With the latest-generation of presbyopia-correcting IOLs, we are able to provide a wide range of vision with an increased freedom from spectacles. I anticipate that in the future, lens technology will continue to improve with every generation of lens being better than its predecessors. The improvement from the original AT-45 to the current Crystalens AO and HD is substantial.

Currently, the Crystalens family of IOLs are the only FDA-approved accommodating, presbyopiacorrecting lens implants available. Using the Crystalens, I am able to meet or exceed my patients' expectations and give them a wide range of high-quality vision. My recipe for success with the Crystalens involves careful pre-operative evaluation, good intra-operative technique, and close post-operative follow-up.

Pre-Operative Evaluation
Biometry

At the pre-operative evaluation, care should be taken to achieve excellent biometry since that is the basis for our IOL calculations. With the advent of optical methods to measure the axial length, such as partial coherence interferometry, the percentage of patients achieving an accurate post-op refractive status (goal +/− 0.50D) has increased, but this is for the spherical equivalent only. In order to maximize the patient's visual results, we need to address the corneal astigmatism to ensure that it is approximately 0.50D or less for most cases.

IOL Calculations and Target Refractions

Patient happiness with the Crystalens is directly related to the post-op refraction — the closer to plano, the happier the patient. Because cataract surgery is a type of refractive surgery, it is critical for surgeons to hit the refractive targets. Thus, we must track our results and hone our lens calculations and A-constants. This can be done quite easily via the DataLink website (SurgiVision Consultants Inc.), which is a simplified and free way to track surgical data.

The suggested A-constants for the Crystalens HD (118.8) and the Crystalens AO (119.1) are good starting points. For the calculations, the SRK-T formula is recommended for axial lengths greater than 22.00 mm, with the multi-variable Holladay 2 formula used for smaller eyes, which have an axial length of less than 22.00 mm. In an analysis of my patients, I found that the typical accommodative amplitude with Crystalens implantation was about 1.50D to 1.75D. With this in mind, the dominant eye should be targeted as close to plano as possible and the non-dominant eye targeted for a slight amount of residual myopia, approximately -0.50D, in order to further enhance the near vision. This will give sharp distance vision, great intermediate vision, and good near vision, resulting in happy patients.

Astigmatism Planning

Reports from DataLink demonstrate that the Crystalens HD and AO Accommodating IOLs perform best with �0.50D or less of myopia or hyperopia and minimal cylinder. Figure 1 shows the induced blurriness a patient sees with just 1.00D of astigmatism (cylinder) versus plano with no cylinder at distance and near. Thus, �0.50D for both sphere and cylinder is the surgical goal. Evaluate the pre-operative corneal astigmatism using both keratometry as well as topography.

Figure 1. The effect of the temporal clear corneal phaco incision must be factored into the astigmatism correction. Before surgery this patient has 1.00D of with-the-rule (WTR) corneal astigmatism. The phaco incision will cause further flattening at the 180° meridian which will increase the astigmatism to 1.5D WTR, therefore LRIs need to be made in order to treat this new amount of 1.5D.

In the future, we may have toric accommodating IOL designs, but for now we need to directly address the corneal astigmatism by adjusting incisional methods. For small degrees of corneal astigmatism, 0.75D or less, we can modulate the astigmatism by varying the placement of our clear corneal phaco incision. Since most sub-3 mm, clear corneal phaco incisions cause a flattening of about 0.5D, we can place this incision on the steep axis of the cornea to address the astigmatism.

It is critical to know the effect of your incision — how much corneal astigmatism it induces. This can be calculated relatively simply using the data from your last 10 or 20 surgeries. Most clear corneal cataract incisions of approximately 2.8 mm width cause about 0.50D of corneal flattening at that meridian.

For more significant degrees of astigmatism (1.0D or more), the use of limbal relaxing incisions (LRIs) is recommended. A key consideration when making the LRI is additive effects of your clear corneal incision. The flattening effect of my phaco incision is also factored into the LRI nomogram. If a patient's preoperative refraction is 1.00D steep at 90°, making the phaco incision at 180° would further flatten the corneal curvature and actually increase the cylinder at 90°. Therefore, I would need to create LRIs for 1.50D at the 90° meridian.

Figure 2. An LRI is created at the 90-degree meridian by using a diamond blade. The fixation ring provides stability of the globe and is marked in clock hours (30 degree segments) to provide a guide for incision length. The steel footplate of the diamond blade glides along the fixation ring to produce smooth, accurate incisions.

I favor LRIs to correct up to 1.50D of astigmatism and laser vision correction to treat 2.00D or more. Analyzing the effect of the LRI topography can be done before and after undergoing astigmatic correction and compared. Remember that although LRIs can be effective with a relatively simple nomogram, older and younger eyes react differently to these incisions.

To help me align my LRIs, I designed a fixation ring with Bausch + Lomb Storz that is marked with clock hours. I simply trace the metal foot plate of the blade along the fixation ring to achieve perfectly smooth and arced LRIs every time. Finally, remember that LRIs are not made at the limbus; rather they are made in the peripheral clear cornea, about 1 mm central from the limbal vessels.

With the post-op goal of plano achieved, with minimal corneal astigmatism, the patient will recover sharp distance vision. The near vision, however, is often a function of the anatomic positioning of the IOL in the eye.

Intra-Operative Technique
Anatomic Considerations

The accommodating IOLs are designed to move, flex, arch, and/or change curvature in response to the accommodative effort of the ciliary muscles. This requires the lens to be securely positioned but not restricted by the capsular bag. Because of fibrosis, the capsular bag tends to contract and shrink-wrap the IOL that may decrease the level of near vision that patients recover.

In a single-focus IOL, we want the anterior capsular rim to cover the edge of the optic in order to securely hold it within the capsular bag. For the currently available Crystalens IOLs, I prefer to have a capsulorhexis that is slightly larger than the IOL optic so that the maximum range of accommodation can be achieved. I prefer a 6.0 mm capsulorhexis in order to allow freedom of the 5.0 mm optic. This slightly larger capsulorhexis, which allows the IOL hinges more mobility, may prove to be of benefit.

Make sure the IOL is fully positioned within the capsular bag, including all four footplates. The best way to ensure that the lens is in the capsular bag is to spin it — it should rotate completely. If the pupil is small, lift up the iris and directly visualize the four footplates to ensure that they are all fully within the capsular bag.

Intra-operatively, the IOL should be placed so that it is vaulted posterior in order to have accurate IOL calculations since the effective lens position largely determines this. In addition, it is thought that the best visual results and accommodative amplitude are achieved with this lens positioning. Note that if the anterior chamber deflates at the end of the case, simply re-inflating it with balanced salt solution is not enough — you must re-position the IOL so that you are sure that the haptic footplates are at the capsular bag equator and the optic is vaulted posterior. To keep the IOL in this position, it's imperative that your incisions are completely water-tight at the end of the surgery.

Test your incisions to make sure they are sealed completely since any tiny leakage could result in a deflated anterior chamber with subsequent anterior displacement of the Crystalens. The best way to fix a leaky incision is not with more hydration, but simply with a suture.

Figure 3. At the end of the case, the capsulorhexis (red outline), which is about 6 mm in diameter, does not overlap the edge of the optic. The main temporal corneal incision and paracentesis incisions (blue outline) have been sealed and deemed water-tight. And the LRIs (green lines), are seen in the peripheral clear cornea at the 90° meridian.

Decrease Complications

Take any measures necessary to minimize complications, either intra-operatively or peri-operatively. To decrease the risk of capsular rupture, make sure that the fluidic settings on your machine are optimized to minimize surge. This means keeping the inflow of fluid significantly higher than the outflow of fluid throughout the entire case. A soft, silicone-coated I/A tip is useful and helps to avoid metal instruments from contacting the delicate posterior capsule.

To keep the macula pristine and to help control post-op inflammation, I like to use NSAIDs for every patient. I use them preoperatively for 3 days and then post-operatively for 6 weeks after surgery to control post-op inflammation, increase patient comfort, and decrease the risk of cystoid macular edema.

Lens Implant Position

Since effective lens position determines the refractive outcome of the surgery, the posterior vault needs to be achieved in order to improve accuracy. You should be able to see the gap between the lens and the iris intraoperatively. Post-op, the slit lamp light reflex should show a space between the iris and the anterior surface of the Crystalens optic. Failure to achieve the correct effective lens position will cause the patient to miss the refractive target and anterior displacement of the Crystalens will induce a myopic shift.

Post-Operative Follow-Up
Residual Refractive Error due to the Cornea

Approximately 10% to 15% of premium IOL patients need a post-operative enhancement to optimize their refractive target. I explain this rate to my patients by telling them that I can place the IOL in a perfect position within their eye, but I cannot predict how their eye will heal. I also tell them that if they do require a post-op touch-up, I will happily do what it takes to help them achieve their goal of sharp vision.

If the patient's vision still is not sufficiently sharp after the LRI procedure, LASIK can fine-tune it, but may also cause dry eye. Even with a well-formed phaco incision, a beautiful femtosecond flap, and a plano result, corneal dryness can compromise the visual acuity, so make sure to prepare the cornea appropriately with tears and perhaps oral omega-3 fatty acids before proceeding with this option.

For residual spherical error, if the patient's refraction is close to plano (20/20 to 20/30) and the patient is happy, do not enhance him. If he has 20/40 myopic or hyperopic vision, determine whether he prefers stronger vision at distance or near, and then enhance him appropriately. Be sure to lock the IOL into position by performing a Nd:YAG laser capsulotomy prior to doing a corneal refractive procedure such as LASIK or PRK. If the excimer enhancement is done first, then months later the patient develops a posterior capsule opacification, the refraction can change once the YAG capsulotomy is performed. For significant post-operative hyperopia, a piggyback lens or IOL exchange may be the best option.

Capsular Contraction Causing Refractive Error

Another common source of residual astigmatism is capsular bag opacification and contraction which can cause the IOL to shift. Lenses that are accommodating in nature, such as the Crystalens, are more flexible and may shift or tilt within the capsular bag, inducing a change in the refractive state of the eye. Modulating the lens position and refraction using the Nd:YAG laser is an important part of achieving good results with the Crystalens.

Figure 4. The small capsulorhexis in this patient has led to capsular phimosis, which has pushed and tilted the Crystalens optic posterior, inducing a hyperopic shift and refractive astigmatism. Using a YAG laser to release the tension on the anterior capsular rim by making relaxing incisions at the cardinal meridians can help to reposition the lens and improve vision.

Figure 5. Fibrotic bands along the posterior capsule have shifted the lens optic anterior and induced optic tilt, resulting in induced myopia and astigmatism. Using the YAG laser to open the posterior capsule and release the tension along the fibrotic bands will help to flatten the lens, return it to a more appropriate position in the eye and improve vision.

A tilt of the lens optic can induce refractive astigmatism. This can be measured be comparing the cylinder of the refraction to the corneal astigmatism. Significant refractive astigmatism in the absence of cornea astigmatism can indicate a tilt of the optic. Capsular phimosis, or contraction of the anterior capsular rim, can cause the lens to be shifted posterior in the capsular bag, which induces a hyperopic shift to the refraction. Using the Nd:YAG laser to perform relaxing incisions of the anterior capsular rim can release the tension of the phimosis and allow the optic to return to its appropriate position, bringing the refraction closer to plano.

Fibrosis of the posterior capsule can cause the lens optic to be pushed anteriorly, resulting in a myopic shift to the refraction. In this case, releasing the tension of these fibrotic bands via a posterior capsulotomy can aid in returning the optic to a more appropriate position away from the iris, again bringing the refraction closer to plano. Initial energy levels should be low, starting at about 1 mJ and titrating upwards as needed. Judicious use of the Nd:YAG laser should be employed since it is relatively easy to bring the patient back for further treatment, but once laser shots are placed into ocular tissue they cannot be undone.

By carefully applying the Nd:YAG laser, we can improve the vision of our cataract surgery patients by clearing the visual axis as well as modulating the position of the lens within the capsular bag.

If you would like to read more about YAG techniques, Bausch + Lomb has a booklet by Harvey Carter, MD, which explains the YAG techniques in detail.

Tune Up the Ocular Surface

A healthy ocular surface is paramount to good outcomes with presbyopia-correcting lenses. Examine eyes pre-operatively for any signs of blepharitis, epithelial membrane dystrophy, or other surface issues. When planning for post-op enhancements, keep in mind that LASIK performed after Crystalens implantation can cause significant dry eye (and most presbyopic patients have dry eyes to begin with). Make sure to explain this risk to the patient, or he will think that your surgery caused his ocular dryness.

Remarkable Results

With careful pre-operative assessment, meticulous intra-operative technique, and close post-operative follow-up, the visual results with the Crystalens can be remarkable, giving a wide range of high quality vision and increased independence from spectacles. We need to leave every eye in focus by achieving a near plano result with minimal astigmatism and we need to minimize any complications that could adversely affect the vision. But most importantly, we need to educate our patients so that they know what to expect after surgery.

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Dr. Devgan is in private practice at Devgan Eye Surgery in Los Angeles, Beverly Hills and Newport Beach, Calif. Dr. Devgan is also Chief of Ophthalmology at Olive View UCLA Medical Center and an associate clinical professor at the Jules Stein Eye Institute at the UCLA School of Medicine. He is a consultant to Abbott Medical Optics, Bausch + Lomb, Hoya Surgical Optics and Ista Pharmaceuticals; a speaker for Accutome, Allergan, Alcon Laboratories, Haag-Streit and Zeiss; and a stockholder in Alcon Laboratories, Ista Pharmaceuticals, Renaissance Surgical and Specialty Surgical. Dr. Devgan can be reached at devgan@gmail.com.