SOFT LENSES FOR IRREGULAR CORNEAS
Managing Irregular Corneas with Soft Contact Lenses
Several categories of soft contact lenses can provide both vision and comfort for irregular cornea patients.
By Mary Jo Stiegemeier, OD, FAAO (Dipl.)
I have been treating keratoconus and irregular corneas for 31 years. For almost all of those 31 years, I have viewed the treatment plan of irregular corneas with contact lenses as a continuum; it begins with the initial diagnosis that is correctable with spectacles and soft contact lenses, including disposable soft toric lenses, but then it progresses to standard rigid lenses, specialty rigid lenses, hybrid lenses, piggyback lenses, mini-scleral lenses, and scleral lenses. As the ectasias or irregularities progress, the fitting process becomes more difficult, more time consuming, and more expensive.
The Modern Role of Soft Lenses for Irregular Cornea Patients
But today, there are a number of ways to utilize soft lenses in the care of irregular cornea patients. In the past, we’ve used higher-modulus soft lenses to mask irregular astigmatism in the early stages of keratoconus, and we have used soft lenses as a base lens in piggyback lens systems, which still continues to work very well for managing keratoconus.
However, these options may not be enough as a patient progresses in the disease process. In recent years, new soft lens designs have become available that can help extend patients’ wear time, improve comfort and physiology, and change that contact lens continuum. Today, advances in both specialty soft contact lenses and in our knowledge of the corneal, limbal, and scleral contour make this possible, as specialty lens laboratories can customize soft lens powers, thickness, peripheral systems, diameter, and toricities to help improve patients’ vision, comfort, and wearability.
I will present three case examples to demonstrate how I used either specialty soft lenses (customized) or frequent replacement lenses to solve fitting problems that patients had with comfort, vision, or their ability to wear contact lenses.
Case 1: Specialty Soft Lenses
A 57-year-old patient had been diagnosed with keratoconus in his mid-20s. The topography map of his right eye showed a very steep forme fruste keratoconus, but the left eye demonstrated a more pronounced penetration of the disease to a global cone condition (Figure 1). His manifest refraction was OD –4.75 20/20, +1.50 J1 and OS –4.25 –6.00 x 131 20/30-3, +1.50 J2-. This patient had been a long-time successful GP lens wearer. However, as the left corneal ectasia and steepening progressed, the left lens was refit multiple times to accommodate for these changes. Over time, this patient suffered from reduced wear of his left lens as a result of discomfort during lens wear; he lapsed into periods of interrupted left lens wear and has had to bear the associated expense from loss of work. In addition, he was dissatisfied that he could not count on being able to wear his lenses.
Figure 1. Topography maps of the patient in Case #1.
For patients such as this, a soft lens option is an exciting prospect because it can offer improvements in comfort, vision, and quality of life. I proceeded to fit this patient in NovaKone (Alden Optical) lenses.
The approach to fitting this lens design is straightforward. First, determine the base curve (using the average central keratometry reading). Then, determine the IT factor: the lens thickness, which effectively manages corneal irregularity. Next, determine the lens power. This lens has front-surface aspheric optics to correct spherical aberration, and residual cylinder can be corrected with the toric design, which uses dual elliptical stabilization to help ensure orientation and rotational stability. Finally, determine the fitting curve: a paracentral curve that helps ensure good lens movement and fit.
I fit the right eye with a spherical NovaKone lens in the following parameters: 8.6mm base curve radius (BCR), 15.0mm diameter, 0 IT, –4.00D power, and 8.6mm fitting curve. The patient easily achieved 20/20 acuity with this lens.
On the left eye, I placed a NovaKone lens with parameters of 8.6mm BCR, 15.0mm diameter, 0 IT, and 8.6mm fitting curve. This lens centered well and moved approximately 1.0mm in central gaze, but the vision was unstable, and topography over the lens still showed irregular mires. I therefore increased the IT factor to a 1. With an over-refraction, this lens yielded 20/30+ acuity.
I then dispensed a lens with parameters of 8.6mm BCR, 15.0mm diameter, 1 IT, –1.75 –5.00 x 140 power, and 8.6mm fitting curve. Two weeks later, the patient was extremely comfortable but needed a modification to the left lens power to accommodate a slight nasal rotation.
The final left lens had parameters of 8.6mm BCR, 15.0mm diameter, 1 IT, –2.00 –5.50 x 144 power, and 8.6mm fitting curve. Visual acuity was 20/20, with a progressive reading Rx of OD plano +1.75 J1, OS plano +1.75 J1.
This patient was thrilled with his vision, he was comfortable, he could wear his contact lenses for 14 to 16 hours consistently without removal, and his eyes remained white until the late hours of the day. Moreover, he could wear his lenses the next day, not needing to take an occasional break from lens wear due to discomfort or fatigue.
Case 2: Piggyback Lens System
This case is an example of a patient who is simply GP lens intolerant. Like the patient in Case 1, this patient suffered from reduced wear of his contact lenses, interrupted wear, loss of work, and inability to depend upon contact lens wear for his correction. His topography map also showed forme fruste keratoconus, with a progressively steepening right topography over time (Figure 2). This patient’s previous glasses had a prescription of OD +0.75 –4.00 x 055, 20/400 and OS +0.50 –1.00 x 100, 20/20.
Figure 2. Topography maps of the patient in Case #2.
A further complication for this patient, as is the case for many patients who have keratoconus, was a large degree of anisometropia. This patient’s habitual correction was a GP lens in the right eye. He was uncorrected in the left eye.
The patient’s habitual right contact lens was manufactured in Boston ES (Bausch + Lomb) and had parameters of 7.40mm BCR, 9.0mm diameter, 7.8mm optical zone diameter, –1.00D power, 8.4mm/0.4mm width secondary curve, and 0.21mm center thickness. His corrected vision in this eye was 20/25.
I ruled out refitting him with another GP lens because the fit of this current lens was as near to an alignment fit as could be expected with the keratoglobus corneal contours, and there was no harsh bearing on the apex of the cone or evident edge impingement. I offered hybrid, piggyback, scleral, and specialty soft lens options. The patient and I selected piggyback fitting because he was already comfortable with applying and removing a rigid design.
To fit a piggyback lens system on a patient who has already worn a well-fitted rigid lens, apply your favorite single-use soft lens to the eye that you are fitting. Take topographical measurements both before and after applying the soft lens, and if possible, record the corneal thickness measurements at various areas around the cornea using topography or pachymetry.
When prescribing the base soft lens, I think about oxygen transmission, discard cycle, and handling challenges. I typically select a single-use, higher-Dk soft lens in the steepest of the base curves offered and in the power that is the sphero-cylindrical equivalent of the patient’s best manifest refraction. A Biotrue Oneday (B+L) lens with 8.6mm BCR, 14.2mm diameter, and –1.00D power worked well in this case. The power of this lens helps in a number of ways. A base lens in this power may allow patients better “walking around” visual acuity when they are not wearing their rigid lens, and it may improve the ability to see more clearly to apply, remove, and care for their lenses.
First, apply this base soft contact lens. If it centers and moves about 1.0mm to 1.5mm in upgaze and is comfortable for the patient, I move to the next step, which is application of the GP lens.
There are three methods that work very well to fit the rigid contact lens and significantly reduce chair time. For fitting purposes, think of the anterior surface of the soft contact lens as now equivalent to the anterior surface of the cornea.
Method 1: If a patient has been wearing a GP lens, simply apply this lens, after cleaning, over the soft lens, using a soft lens solution. This resulted in a successful fit for our patient.
Method 2: Use topography or keratometry values over the soft lens to fit a rigid lens, again assuming that the anterior surface of the soft contact lens is now equivalent to the anterior surface of the cornea. Begin with a base curve that is slightly steeper than the flat topographical reading.
Method 3: Simply start with a known base curve and diameter of average measurement—approximately 45.00D BCR and 9.0mm diameter—and evaluate that fit.
In all three cases, remember several GP caveats. GP lenses will move more and ride higher when they are too flat or too loose. Conversely, GP lenses will move less and ride lower when they are too steep or too tight. In keratoconus cases, the GP lens will typically center and move much better with the soft lens in place, but remember that the rigid lens will still migrate to the steepest area of the cornea. Also remember that a lower-specific-gravity rigid lens will center slightly higher, and a higher-Dk lens is preferred.
Figure 3. Topography maps of the patient in Case #3.
Think about hygiene and frequent replacement. The rigid contact lens should be replaced at least annually, but can be replaced every six months or quarterly; the soft lenses should be replaced daily. There is no need to use high-molecular-weight fluorescein to fit these lenses, although you can use it if you prefer. Record the vertical and lateral centration as well as the movement of both the rigid and the soft lens.
Once you are satisfied with the fit, over-refract this lens system. Remember that the anterior surface of the rigid contact lens is the limiting factor for the power of this lens system. The rigid lens will somewhat neutralize the power of the underlying soft lens—the powers are not additive. Therefore, over-refract by spheres only at first; if visual acuity is good, add your power to the rigid contact lens, with consideration of vertex distance. If visual acuity is not good, perform a sphero-cylindrical over-refraction and a topographical map over the piggyback lens combination. If the map and the sphero-cylindrical over-refraction are equivalent, the rigid lens is flexing on the eye. Increase the center thickness of the rigid contact lens by about 0.04mm to reduce the flexure; do not add the cylindrical component to the power.
Case 3: Custom Soft Lens
This case is an example of a keratoconus patient who was wearing soft toric lenses, but was undercorrected. This patient had severe keratoconus in the right eye and forme fruste keratoconus in the left eye. He was currently wearing a soft toric lens that was comfortable, but was under-correcting the cylinder and not correcting the irregular astigmatism. His contact lenses had a back-surface toric design with –3.25D cylinder correction and were manufactured in methafilcon A (55% water content) material.
The patient’s manifest refraction was OD +2.25 –4.25 x 068, 20/30+2 with ghosting and halos, OS 0.00 –1.00 x 072, 20/20.
This patient was comfortable with a soft toric lens and had very acceptable vision in the left eye. I decided to refit his left eye in a higher-Dk lens that offered more frequent replacement, with parameters that could be expanded as necessary if there was progression. I chose Air Optix Aqua for Astigmatism (Alcon), manufactured in lotrafilcon B (33% water) material, in parameters of 8.7mm BCR, 14.5mm diameter, –0.25 –0.75 x 080, 20/20.
I fit the right eye with a SpecialEyes Toric hioxifilcon A (59% water) lathe-cut toric lens in parameters of 8.2mm BCR, 14.4mm diameter, +2.50 –3.75 x 066, 20/25+2.This patient was extremely happy with the improvement in vision while maintaining comfort and physiology.
More Options = Better Fitting Success
In conclusion, I love the challenges that fitting irregular cornea patients presents, and I am happy that we have a broad array of options that I can offer my patients to improve their quality of life. CLS
Dr. Stiegemeier is the founding member of Western Reserve Vision Care, a private optometric practice in Beachwood and Hudson, Ohio, where she specializes in therapeutic contact lens fitting. She also is staff optometrist at the Cole Eye Institute, Cleveland Clinic Foundation, Specialty Contact Lens Clinic, Department of Ophthalmology. In addition, Dr. Stiegemeier is an adjunct assistant clinical professor at Pacific College of Optometry and an adjunct assistant professor at University of Missouri - St. Louis.