Applications of CK and pearls for postoperative management

The Food and Drug Administration has approved conductive keratoplasty for treatment of both presbyopia and hyperopia. However, other potential off-label applications for CK exist. These off-label applications include enhancement of LASIK, PRK or pseudophakic outcomes, neutral pressure CK and the treatment of astigmatism or mild keratoconus.

CK for LASIK enhancement

It is imperative for ophthalmologists to be aware of patient criteria and contraindications before deciding to use CK for LASIK enhancements. Patients must be appropriately selected and must meet specific requirements. For example, patients’ pre-LASIK refractive error, their status as either hyperopic or myopic, as well as their peripheral corneal pachymetry, must be determined. A peripheral corneal pachymetry greater than 560 µm is required for CK and flap integrity must be closely investigated to ensure the patient has no history of diffuse lamellar keratitis.

If significant striae are present, spots that are placed during CK pull on the cornea and may worsen the condition. Additionally, it is not recommended to apply CK spots in an area of epithelial ingrowth. Also, ophthalmologists should be conservative with eyes that have already been treated with PRK or LASIK for myopia. The majority of patients whom I have treated with one ring at 7.5 mm or 8 mm have had good results. In a few cases, I have found that one ring of spots at 9 mm has been sufficient, but more research is needed to verify this nomogram.

Case studies

One particular patient on whom I performed LASIK 5 years ago had an original refraction of -9 D. For an unknown reason, she had induced against-the-rule cylinder of 3 D. I attempted limbal relaxing incisions and noticed approximately 0.5 D of effect. She had good visual acuity in the fellow eye but was somewhat unhappy. I did not want to relift her flap because I was unsure of the stromal bed thickness, which was not measured previously.

Instead, I administered two spots of CK at the 7.5-mm optical zone at the 6 o’clock and 12 o’clock positions initially and administered two more spots placed at the 6.5-mm optical zone later. Currently, her uncorrected visual acuity is 20/25. When informed that her vision would most likely regress as her eyes continue to age, she replied, “Fine. I would do it 100 times because this is the easiest thing I have ever done, and it is much easier than the LASIK.”

Ophthalmologists should be conservative with eyes that have already been treated with PRK or LASIK for myopia. The majority of patients whom I have treated with one ring at 7.5 mm or 8 mm have had good results. In a few cases, I have found that one ring of spots at 9 mm has been sufficient, but more research is needed to verify this nomogram. – Helen K. Wu, MD

A second, more typical CK patient who previously had PRK for 7 D of myopia, was originally overcorrected to 2.25 D and regressed to approximately 1.5 D. He eventually struggled to see 20/30 in that eye and desired better near vision. I administered eight spots at 8 mm to enhance his near vision and correct his overcorrection. He displayed 20/20 distance vision and 20/25 near vision in the corrected eye and was extremely content.

CK can also be used to enhance pseudophakic patients. I treated a patient who received an IOL in both eyes, had 20/20 to 20/25 uncorrected distance vision and was J16. She was dissatisfied because she could no longer read the newspaper without glasses. I placed eight CK spots at 7 mm in the treated eye, which resulted in the patient’s achieving J3 and -1.5 D in that eye, a result with which she was highly satisfied. The majority of surgeons will encounter this type of patient after cataract surgery.

An example of a patient who is a candidate for CK because of contraindications for other procedures is a 51-year-old woman whom I followed for more than 12 years. She suffered from benign lymphoid hyperplasia of the conjunctiva, had been treated with radiation 10 years previously and has been on chronic steroid use ever since. She developed cataracts and had an elevated IOP, for which she took timolol.

Additionally, she has experienced persistent punctate keratopathy, which only marginally improved after applying artificial tears and Restasis (cyclosporine ophthalmic emulsion, Allergan, Inc.). I performed cataract surgery and found that, postoperatively, she was reasonably content. However, she had a preexisting with-the-rule cylinder of 3 D. CK was chosen due to existing ocular surface disease and the possibility of steroid response after PRK. I was unwilling to perform AK because of her previous radiation keratopathy. LASIK was an obvious poor choice of treatment due to her keratopathy and dry eye.

For this patient, I selected CK and placed two spots at the 7-mm optical zone at the 3 o’clock and 9 o’clock positions. Initially, her uncorrected visual acuity (UCVA) improved to 20/40, her cylinder improved 0.5 D and she experienced mild irregular astigmatism, which subsequently resolved. She currently enjoys 20/25 vision and reports being highly satisfied with her results.

NearVision CK with LightTouch

When I first began performing CK, I experienced variable success. Some of my patients were content but, other patients, particularly those with thicker corneas, had undercorrection or no correction at all, even with 24 spots. Initially, I found that I was pushing hard on the cornea when performing CK and, when nothing was accomplished, I mistakenly thought I was not pushing hard enough. In fact, the exact opposite was true. NearVision CK with LightTouch is a corneal compression technique in which surgeons should apply minimal pressure to the cornea. The application of light pressure allows the cornea to be in closer apposition to the probe and allows for a larger leukoma and a greater effect. Typically, 80% of patients require only eight spots, compared to 24 spots with traditional CK, at either the 7-mm or 8-mm optical zone.

While the stability of NearVison CK with LightTouch has not been established, my results over the past 6 months show that this technique has better results than laser thermal keratoplasty (LTK) and the conventional CK technique. With LTK, there is a large myopic overcorrection initially and significant regression after 6 months. – Helen K. Wu, MD

The initial effect of NearVison CK with LightTouch is robust and the potential for greater compromise of UCVA at distance exists. Initially, there is a significant myopic shift if no adjustment to the conventional CK nomogram is made. Currently, there is no proven nomogram for CK with LightTouch, but physicians should develop their own personal nomograms.

The major advantages of NearVision CK with LightTouch include treatment applied at a larger optical zone, therefore producing much less induced astigmatism and making results more consistent. Patients may experience less nighttime glare, and more opportunities for additional enhancements exist.

While the stability of NearVison CK with LightTouch has not been established, my results over the past 6 months show that this technique has better results than laser thermal keratoplasty (LTK) and the conventional CK technique. With LTK, there is a large myopic overcorrection initially and significant regression after 6 months.

Table 1 compares the differences in the nomograms of conventional CK and NearVison CK with LightTouch. The main difference is that in conventional CK, 24 spots are typically used for an effect of 1.75 D. With CK with LightTouch, eight spots at 7 mm are used for an effect of 1.75 D. The nomogram that represents CK with LightTouch in Table 1 is similar to the one that I use when performing CK with LightTouch.

	Table 1: Comparison of conventional CK and Milne nomograms (NearVision CK with LightTouch technique). Courtesy of H.L. Rick Milne, MD

Surgical technique

Some similarities between NearVison CK with LightTouch and conventional surgical techniques exist. For example, when performing LightTouch, ophthalmologists should first mark the cornea and fully seat the probe in the cornea. As shown in Figure 1, consistency is imperative. With LightTouch, the cornea should be allowed to relax into its neutral position before the pedal is depressed. Since the cornea will actually shrink away from the probe, it is important that the probe remain seated deep in the stroma as the energy is applied. In my experience with CK with LightTouch, I have not had to place a bonus spot on most cases. This is in marked contrast to my experience with conventional CK, where I placed bonus spots at least 20% of the time. NearVison CK with LightTouch has made a significant difference in how I view CK and I have found a much higher rate of patient satisfaction.

	Figure 1: Eyes should be marked in the exact center to maintain consistency. Courtesy of Daniel S. Durrie, MD

Postoperative management

Patients who have had a recent neutral-pressure CK procedure generally do not experience discomfort. However, patients may experience a mild foreign body or pressure sensation, but often do not require pain relievers. In more severe cases, I recommend that a 0.05% tetracaine solution be used aggressively. Cold compresses are also helpful and chilled artificial tears may be used as needed. Patients should wear sunglasses because of the possibility of postoperative iritis, which can lead to discomfort. Also, an ophthalmologist may decide to prescribe narcotics if a patient requires a significant amount of attention. However, the majority of patients who are prescribed narcotics do not put them to use.

Patients do not typically experience discomfort 4 to 6 weeks postoperatively. Patients’ binocular near and distance UCVA should improve significantly, a ring of striae with no edema at the slitlamp should be visible and refraction may not correlate well with effect. – Helen K. Wu, MD

A 1-day postoperative office visit is recommended for patients, but a phone call is also acceptable, depending on insurance standards. It should also be emphasized that patients have minimal restrictions. Although it is not recommended for patients to swim on the first postoperative day, they are generally able to return to their normal lives in a short time.

Patients do not need to use their old high-power reading glasses, but they may need to use a pair of low-power glasses. This can help them to better understand how their vision improvement is progressing. In the first few postoperative weeks, it is important to reassure patients that their vision results will fluctuate. The majority of patients report high satisfaction with their results 1 month postoperatively. If patients are dissatisfied with their vision outcomes, physicians should inquire as to their functional complaints (location, time of day, lighting conditions and associated activities where problem occurs; examples of patient techniques to improve the problem and examples of specific vision improvements obtained) and identify simple solutions. If patient dissatisfaction is due to undercorrection, it is advisable to discuss further steps that may be taken for vision enhancement. If night driving becomes a problem, glasses may be necessary for driving.

Functional complaints depend on the time of day, the lighting conditions and the associated activities. It may also be necessary to remind patients that the goal is J3. For example, patients should realize that they should not expect to be able to read a map in low light conditions while in their car late at night.

Patients do not typically experience discomfort 4 to 6 weeks postoperatively (Figure 2). Patients’ binocular near and distance UCVA should improve significantly, a ring of striae with no edema at the slit lamp should be visible and refraction may not correlate well with effect. This may be due to a multifocal corneal effect seen after CK that produces better than expected near vision. Any induced astigmatism should be documented and treated within the first few months postoperatively, if necessary. However, it is imperative not to enhance too soon after a CK procedure, because the majority of induced astigmatism will dissipate.

	Figure 2: CK Decision Tree at 4 to 6 weeks postoperative Courtesy of Helen K. Wu, MD

Enhancement profile

Generally induced astigmatism and undercorrection are the primary causes for CK enhancement. I estimate that my rate of enhancement has dropped to less than 5% since I began using CK with LightTouch. It is normal that ophthalmologists will perform more enhancements in the beginning of their learning curve. Approximately 5% of patients will be undercorrected and it is critical to treat the patient’s symptoms and not the refractive outcomes because they do not tend to correlate. Undercorrection most likely occurs when patients are younger and require greater steepening of the cornea. Induced astigmatism can cause patient dissatisfaction, so ophthalmologists must address the issue earlier, rather than later.

If a patient’s UCVA at near is not J3 or better and the patient is dissatisfied, he or she is most likely undercorrected and typically will require additional rings of CK treatment or PRK. – Helen K. Wu, MD

If a patient is within 1 D of the refractive target, he or she will most likely need only eight more spots at either 7 mm or 8 mm with NearVison CK with LightTouch. If a patient has a refractive error greater than 1 D, ophthalmologists should consider performing PRK. I have had to perform PRK on a few occasions and have found it to work well over CK. I do not recommend LASIK over CK, since the creation of the flap involves cutting through the bands of collagen shrinkage. Nevertheless, LASIK has been performed successfully after CK by others.

With astigmatism, it is important to be cautious with the NearVision CK with LightTouch technique because surgeons can get much more of a refractive effect than expected based on their previous nomogram. If an ophthalmologist performs a conventional CK procedure and the patient develops induced astigmatism, it is usually better to enlarge the optical zone when applying neutral-pressure CK spots as an enhancement.

The majority of patients are satisfied if J3 or better functional vision exists after the initial CK procedure. If a patient’s UCVA at near is not J3 or better and the patient is dissatisfied, he or she is most likely undercorrected and typically will require additional rings of CK treatment or PRK. If induced cylinder is greater than 2 D, a bonus spot should be added with caution.

The keys to success in CK are to reinforce the functional goals over the refractive goals, to listen to the patient, measure patients less and to address the unmet clinical outcomes early and positively.