SPECIALTY LENS FITTING
Advanced Concepts in Fitting Contact Lenses
Learn new approaches for providing optimal acuity and cosmesis to patients who require specialty lenses.
By Jeffrey Sonsino, OD, FAAO
When complicated contact lens patients find your practice, it's important to fit them efficiently, paying particular attention to vision and comfort. Nothing is more exciting to a patient who has persevered through a long course of therapeutic treatment, complex surgical procedures or vision impairment as when they can see well. As contact lens specialists, we're particularly poised to provide an almost immediate benefit to patients who have complicated ocular conditions. Post-penetrating keratoplasty patients have endured months of sub-optimal vision while their corneas heal. When they sit in your chair, you can provide an immediate reward for their months of hardship.
Conditions such as keratoconus, post-refractive surgery, post-penetrating keratoplasty, malignant myopia and aphakia are familiar, but all require different management. I'll discuss new approaches and ideas for achieving maximal benefits. In addition, I'll discuss conditions not usually associated with contact lens practice such as retinopathy of prematurity, congenital glaucoma, ocular albinism, aniridia, correctopia, retinitis pigmentosa and cone/rod dystrophy.
Figure 1. Corneal neovascularization due to an immobile GP lens in a keratoconus patient.
There are few conditions for which contact lens correction is the definitive treatment. Patients who are newly diagnosed with keratoconus and fit with GP lenses will typically have never seen better, while those who have been wearing contact lenses for years can be more challenging.
Fitting GP lenses for keratoconus is similar to fitting GP lenses in general how you arrive at the desired result is just a little more challenging. The lenses should provide acceptable vision, good comfort and a fit that will not produce mechanical abrasion of the epithelium. An alignment fit with a GP lens is optimal, but usually achievable only for very mild cases of keratoconus. From there, aim for light bearing on the apex of the keratoconic cone (the traditional three-point touch) or an apical clearance fit. Patients fit with excessive apical clearance will complain of a fog or haze that develops shortly after lens application.
Between 65 percent to 90 percent of keratoconus patients who wear contact lenses use GP lenses (Szczotka et al, 2001; Barr and Bennett, 2004). Lens designs have become very sophisticated as practitioners and contact lens laboratories have realized the importance of custom designs. Laboratories who are members of the Contact Lens Manufacturing Association (CLMA, www.clma.net, 800-344-9060) have particular interest in helping practitioners utilize custom manufactured lenses.
We use custom keratoconic designs to fit the majority of our keratoconus patients. Our first line for keratoconic lenses includes the AKS (Art Optical Contact Lens, Inc., www.ArtOptical.com, 800-253-9364), Dyna Z Cone (Lens Dynamics, Inc., www.LensDynamics.com, 800-228-2691) and Rose K (Blanchard Contact Lens, Inc., www.RoseKLens.com, 800-367-4009). A diagnostic lens fitting involves more chair time initially, but is the best way to save patient visits and frustration as the process continues.
Fitting piggyback systems is a significantly underutilized technique for keratoconus. A silicone hydrogel lens placed underneath a GP lens provides increased comfort and a barrier between the cornea and rigid contact lens. Better comfort is possible when the upper eyelid rides up the ramp created by the soft lens to glide easily over the GP lens edge. This system can be very powerful when fitting a younger, first-time keratoconus patient. I tell such patients and their parents that the piggyback system will serve as "training wheels" until sufficient comfort is achieved. However, many of my patients use the piggyback system long term.
Figure 1 shows a 47-year-old male keratoconus patient who had worn habitual lenses for three years without re-evaluation. This photograph was taken on his first visit. We diagnosed corneal neovascularization due to an immobile GP lens. We treated him with Pred Forte q.i.d. for two weeks. The vessel became a ghost vessel, but quickly filled again after we refit him with GP lenses. We sent him to a corneal surgeon for Argon laser cauterization of the base of the feeding vessel. Upon recovery, we will refit him in a piggyback lens system consisting of a hyper-Dk GP lens material and a silicone hydrogel to reduce mechanical abrasion.
Hybrid contact lenses are re-emerging as a successful option in fitting keratoconus. New higher-Dk lens materials have made hybrid lenses a safer alternative than in the past. SynergEyes, Inc. (www.Synergeyes.com, 877-733-2012) manufactures the SynergEyes KC lens, a hybrid lens with a Paragon HDS (Dk=100) core and a 27-percent non-ionic hydrogel skirt. Patients properly fit with this lens often boast superior vision, comfort and stability compared to other lenses.
Figure 2. I join the pediatric ophthalmologist in the EUA to perform automated keratometry, retinoscopy and a trial lens fitting with sodium fluorescein on young patients who have significant difficulty with the fitting process while awake.
Following refractive surgery, optical aberrations from the altered corneal shape result in reduced best-corrected visual acuity. Such patients often search for a correction that returns them to their pre-surgical best-corrected visual acuity, so expectations may be higher than in other patient populations.
We've had success using aspheric posterior-surface GP lenses for low corneal eccentricities and large-diameter lenses, such as the Dyna Z Intra-Limbal lens (Lens Dynamics), for flat corneas. The lenses do not need to fit centrally, but must provide pupil coverage and align with the cornea as closely as possible. In one case, a 58-year-old female presented with a decentered radial keratectomy result. She complained of fluctuating, blurry vision that had worsened since surgery. We fit her with a large-diameter GP lens that provided 20/20 stable vision.
Reverse geometry GP contact lenses are often successful following myopic corneal refractive surgery. Hydrogel contact lenses are not optimal for post-refractive surgery corneas because they can't mask corneal irregularities and they are associated with increased risk of corneal erosions (Martin and Rodriguez, 2005). Scleral lenses have also been used, but are not widely available. Martin and Rodriguez showed that after corneal refractive surgery, reverse geometry contact lenses improved visual acuity over spectacles by two lines in five of nine patients, by one line in two of nine patients and offered no improvement in two of nine patients. No demonstrated loss of visual acuity occurred with contact lenses. Patients tolerated the lenses for 10.44 ±0.88 hours each day.
Post-PK contact lens fitting is about as complicated as it gets. As with post-refractive surgery, the main problem is irregular astigmatism. Touzeau et al (2006) studied the changes in optical properties following removal of soon-after to years-after sutures in 64 post-PK patients. Following removal of years-after sutures (76.8 months ±25.2 months), spherical equivalent refraction was –3.30D ±2.98D, defocus was 4.31D ±2.15D, astigmatism was 4.46D ±1.99D and irregular astigmatism was 2.52D ±1.54D. No change occurred in these optical aberrations over time. Gruenauer-Kloevekorn et al (2005) showed that in 28 post-PK eyes, 57.2 percent had spherical power, 96.4 percent had regular astigmatism and all had irregular astigmatism outside of normal range.
Studies of spectacle best-corrected visual acuity fail to address the problem of adaptation to high-cylinder spectacle prescriptions. Javadi et al (2005) stated that a successful outcome for PK surgery includes a refractive error that spectacles can tolerably correct. Although not optimal, clinicians typically prescribe spectacles following surgery.
Five principal GP lens designs are available to fit irregular corneas after PK procedures: Tricurve, keratoconic, tetracurve reverse (geometry), oblong and bitoric (Gruenauer-Kloevekorn et al, 2005). Tricurve lenses have the simplest design and may provide the best opportunity for customizing individual parameters, especially peripheral curves. They are also the most time-intensive and potentially frustrating design. Keratoconic designs fit prolate grafts with high eccentricity and steep base curves. Tetracurve reverse geometry lenses fit oblate grafts with negative eccentricity and feature peripheral curves that you can adjust based on fit. In a case series of 11 patients who had flat corneal grafts, Lagnado et al (2004) found that all 11 patients required reverse geometry lenses for a satisfactory fit. As with tetracurve reverse geometry lenses, oblate lenses feature a reverse curve for oblate grafts, but they also have an aspheric periphery rather than tetracurve peripheral curves. Bitoric designs are indicated for high corneal toricity in the donor tissue.
Pediatric Contact Lenses
Should a child with low vision arrive in your chair, realize that you are the expert whom the child and parents have been seeking. They've most likely heard from other doctors the famous line encountered in low vision: "Nothing more can be done." In most cases, this is simply not true. Even if yours is not a center for visual rehabilitation, your job is to maximize the child's vision potential so that you can make proper referral to such a center. You can frequently accomplish this using contact lenses.
The children you may encounter who need contact lenses will vary in age. How do you determine whether they have the interest and responsibility required to wear contact lenses? For many, yours will be the first presentation of the option of contact lenses. For any child, this decision is multifactorial and depends mainly on the child's disposition. Some who've undergone multiple ocular surgeries are eager to escape their soda-bottle glasses, while others are weary of another doctor approaching their eyes. We've seen kids who were very eager to try contact lenses, but when the fitting process began they bolted out of the chair. Infants are typically easy to fit because they tend to not fight back, but 1- and 2-year-olds are notoriously reluctant to allow practitioners to approach their eyes. After the age of 3, the sky's the limit in terms of personalities you'll encounter.
Once you establish that a child is a candidate for contact lenses, you must determine the desired outcome. You can use contact lenses to correct cases of high astigmatism, myopia or hyperopia and for reducing glare, or you can use them in concert with low vision devices or for other desired results. Regardless of the desired outcome, you must clearly explain benefits and risks to the parents.
High Refractive Error, Microcornea, Malignant Myopia Diagnoses such as retinopathy of prematurity (ROP), aphakia, microcornea, persistent fetal vasculature and malignant myopia often produce high refractive errors in children. These patients will hopefully present to you with spectacles correcting these high prescriptions. If not, amblyopia might be well on its way. In addition to fitting contact lenses, always provide a spectacle prescription for times when these patients cannot wear their contact lenses.
Problems with high-powered spectacle lenses include aniseikonia with anisometropic prescriptions, reduced peripheral optics, chromatic aberrations and prismatic effects, as well as undesirable cosmesis (Borish, 1983). The sum of these optical effects makes contact lenses much more optically viable. Expect improvements in vision anywhere from subjective improvement to a line or two on the Snellen chart. These are significant improvements in this patient population. Kids remark that peripheral vision improves significantly, and parents notice that their kids can better negotiate environments without tripping, falling or bumping into objects.
Figure 3a (top). Retroillumination of ocular albinism. Figure 3b (bottom) shows the cosmetic lens we fit on this patient that is dyed with an opaque tint that blocks paraxial light.
When fitting patients who have high prescriptions, we typically fit GP lenses to allow for longer daily wear time. The difference in visual potential between spectacles and contact lenses is great, so you can bet that these patients will wear their lenses from morning to bedtime. Because Dk data is based on a –3.00D thickness lens, the Dk of a high-powered, thick lens is significantly less. We've had success with GP materials such as Boston EO (Bausch & Lomb) and Menicon Z.
We resort to soft lenses in rare circumstances, but hyper-Dk materials may change that. In the coming months, CIBA Vision will launch a customized silicone hydrogel lens available in parameters ranging from ±20.00D. This will be an exciting time and will likely change the way we fit advanced contact lenses.
Retinopathy of Prematurity With the development of modern neonatology, even the smallest and sickest premature babies are now surviving, but they are also developing ROP. With the incidence of ROP increasing (O'Connor, 2003) and practitioners seeing more of this condition, proper management is becoming more vital.
Epidemiologic studies have shown that 20 percent of very-low-birth-weight infants will develop myopia in the first two years of life. The incidence of myopia is directly related to the severity of ROP. Al-Ghamdi (2004) and Ricci (1999) have reported a high proportion of strabismus, amblyopia, astigmatism and anisometropia with ROP. In addition, retinal detachment in advanced stages with ensuing scleral buckle yields high myopia, sometimes as high as 30.00D. This often results in high anisometropia. Too often, such a patient will present to you in spectacles with one eye vastly undercorrected. When fit with GPs, this patient will notice not only improved peripheral vision, but also increased contrast sensitivity and potentially improved stereopsis.
If a very young child has ROP and anisometropic amblyopia is the concern, then your only option is contact lens correction used in conjunction with patching therapy.
You can also treat high refractive errors with GP lenses. In cases of high astigmatism, the cylinder may be internal. In addition, the dragged macula that often accompanies severe ROP may require off-axis retinoscopy and refractions. Toric hydrogel lenses are the best option for such cases.
Aphakia Anisometropic amblyopia is also the concern in unilateral and bilateral aphakes. Surgeons will often remove cateractous lenses and not replace them with an intraocular lens (IOL) in young children. IOL implantation in children is highly debated in the ophthalmic community. Dr. Franco Recchia, the pediatric retina specialist at Vanderbilt University, states, "In my pediatric retina practice, a common indication to consider secondary IOL placement is visual rehabilitation following surgical repair of retinal detachment related to retinopathy of prematurity, trauma or congenital diseases such as persistent fetal vasculature syndrome. Because of a lack of any capsular support (the capsule is meticulously removed to prevent future contraction or proliferation that may lead to ciliary body breaks or traction retinal detachment), my only option is typically a sutured IOL. In such cases, I prefer to delay surgery until at least school age, when most of the eye growth is complete and children are less likely to rub their eye and dislocate the IOL."
In my practice, we fit babies and young children in GP lenses when Silsoft lenses (Bausch & Lomb, www.bausch.com, 585-338-6000) fail. If necessary, I join the pediatric ophthalmologist in the exam under anesthesia (EUA, Figure 2) to perform automated keratometry, retinoscopy and a trial lens fitting with sodium fluorescein. An EUA provides an opportunity to perform testing on a child who would otherwise resist. In my operating room kit, I include a retinoscope, retinoscopy lens bars, hand-held auto keratometer, GP diagnostic lens set (10 lenses), diagnostic set of Silsoft (5 lenses), lens solutions, sodium fluorescein and exam form. The operating room will be set up with Weckcells and gauze that you can use to manipulate the lenses and tears. Patients are anesthetized by the time I see them. The table is lowered to the floor so I can examine the patient from above. I use a lid speculum to take keratometry readings, then I perform retinoscopy and evaluate both GP and Silsoft contact lenses. I usually have only one opportunity to determine a proper fit. Back in the examination room, children typically allow only minimal inspection.
Congenital Glaucoma Contact lens fitting in children who have glaucoma is controversial. There is very little in the literature on this topic. I've had many discussions with pediatric glaucoma specialists about therapeutic contact lens correction for children who have glaucoma. We do not fit kids who've had a filtering bleb or a secondary glaucoma involving the cornea. We also do not prescribe hydrogel contact lenses in a patient on maximal medical therapy because of a potentially unpredictable drug depot or release effect. That said, we do fit patients who have high refractive errors and those who have undergone tube shunt procedures. We fit GP lenses and monitor these patients closely.
Ocular Albinism, Aniridia, Correctopia, Retinitis Pigmentosa and Cone/Rod Dystrophy In conditions such as ocular albinism, aniridia, correctopia, retinitis pigmentosa and cone/rod dystrophy, glare disability is a major component of visual impairment. Glare is a physical property of a light source. Glare disability is the reduction in visual function from a glare source. The mechanism of glare disability is likely related to decreased contrast sensitivity, image degradation or light scatter within the ocular media (Vos, 2003). Often, kids who have these diagnoses do not have any sun/glare protection. The resultant reflex is squinting, which yields obvious benefits. A pupil-control contact lens accomplishes the benefits of squinting and provides attenuation of glare by blocking paraxial light from entering the eye. Figure 3a shows retroillumination of ocular albinism. We fit this child with a 3mm-pupil cosmetic contact lens (Figure 3b). The posterior surface of the lens is dyed with an opaque tint that blocks paraxial light.
Sources of pupil-control contact lenses include Adventures in Color Technology, Ltd. (www.techcolors.com, 800-537-2845), CIBA Vision's Special Eyes Program (800-488-6859) or, if your demand justifies in-office production, you can obtain the tinting equipment from Softchrome, Inc. (www.softchrometinting.com, 925-743-1285). With children, a mandatory consideration is cost. Assuming that they will lose three lenses per year, replacement costs can add up. Tinting the lenses in-office is the cheapest method. We use opaque Durasoft 3 colored lenses (CIBA) as a base to which we add a black underprint. The cosmesis is fantastic in bilateral cases. In unilateral cases, asymmetry often occurs between the two eyes. In these cases, we switch to a custom-painted lens when the child reaches adolescence and the pressures for cosmesis intensify.
As practitioners, we have a great responsibility to provide our patients with optimal vision. Whether for a simple myope or a post-PK patient, contact lenses can often provide these results. By tailoring each contact lens fit to each patient's specific needs, we can increase both their visual acuity and their confidence. In the past decade alone, manufacturers have made great strides in developing contact lenses that can enhance each person's lifestyle while providing maximum ocular health benefits. It's often the patients who have the most complicated fits that will prove to be your most challenging, as well as your most grateful.
For references, please visit www.clspectrum.com/references.asp and click on document #133.
Dr. Sonsino practices at Vanderbilt Eye Institute where his clinical responsibilities include advanced contact lens practice, adult low vision center and a specialty pediatric low vision clinic as well as primary eye care at the Department of Veterans Affairs.