How to Deal With Difficult Contact-Lens Fits
contact lens fittings
How to Deal With Difficult Contact-Lens Fits
Learn how to identify and address contact-lens fitting challenges.
BY DIANNE M. ANDERSON, O.D., F.A.A.O., Glen Ellyn, Ill.
Many factors contribute to the level of difficulty that a contact-lens (CL) fit may present. These factors are dependent on the patient's corneal and ocular conditions, prescription and demeanor. New contact-lens materials and designs may offer a new set of challenges and discoveries. And, performing corneal topography can inform us of corneal distortions and irregularities, such as astigmatism, that we must address. Once you know a challenge exists, you can approach the CL fitting using the guidance offered here.
Allergies, blepharitis, meibomianitis, persistent keratitis and dry-eye syndrome are very common occurrences in the average practice. These chronic conditions can cause complications with — or become exacerbated by — CL wear. Uncover these conditions during the pretest, so you may deliver proper treatment before or in conjunction with the CL fitting.
Figure 1: This patient displays superficial punctate keratitis (SPK). SPK often results from ocular surface or lid disease such as dry eye syndrome and blepharitis.
Embrace motivated new CL wearers with patience and enthusiasm. These patients will likely require more time for insertion and removal training than your long-time wearers.
Screen patients as they make appointments, so your practice can allot technician time for training. If a patient has an exceptionally difficult time with insertion and removal, reschedule him for another try within a few days.
Assign your most patient technician to children, as these young patients may need extra encouragement. Educate children on their responsibilities for healthy CL wear, such as the importance of following your prescribed cleaning regimen. Prior to the fitting process, have your young patient's parent(s) sign a consent form that reveals he or she not only approves, but will be involved in their child's CL regimen.
Start new CL wearers with a two-week or monthly replacement lens, so they practice CL handling, cleaning and disinfection each day.
If this regimen doesn't suit the patient, refit him with a daily disposable lens (prescription permitting) at a follow-up visit.
Not every patient responds well to silicone hydrogel CLs. Adverse reactions in patients with dry eyes or prevalent lid disease are blurred vision with persistent superficial punctate keratitis (SPK) (see figure 1). Friction from high-modulus silicone hydrogel CLs may cause increased lens awareness and giant papillary conjunctivitis (GPC) or superior epithelial arcuate lesions if the CL edge interferes with the superior limbus. If you discover an adverse condition that you attribute to the contact lens, initiate treatment and consider providing an alternative CL material.
High prescription options
High prescriptions frequently fall outside the parameters of most soft spherical and toric CL prescription ranges, forcing you to choose an alternative material (i.e., rigid gas permeable, hybrid) or replacement modality (quarterly, annual) that will best suit your patient.
To find out more information about high prescription CLs, check Tylers Quarterly Soft Contact Lens Parameter Guide, and talk to your CL sales representatives.
Soft toric challenges
Rotational stability is an issue with CLs on corneas with greater than 2.50D of corneal toricity. Contrary to popular belief, adjusting the base curve and lens diameter are the keys to reducing rotation. Thinking in terms of corneal sagittal height, evaluate the keratometry (K) readings and the horizontal visible iris diameter (HVID).
Given a fixed lens diameter, a cornea with an HVID of 12.5mm and a flat K of 42.00D is best fit with a steep soft toric lens than a cornea with an HVID of 11.5mm and a flat K of 42.00D. Also, a cornea with an HVID of 11.5mm and a flat K of 46.00D may be physiologically compromised by edge seal-off if you fit a large diameter, steep soft toric lens.
Figure 2: Topography map and simulated NaFl pattern of limbal to limbal WTR astigmatism. Toric peripheral curves will help reduce the GP bearing at 2 and 8 o'clock.
Fitting and modifying rigid gas permeable (GP) CLs is as much an art as it is a science. As a result, you must clearly understand lens dynamics and sodium fluorescein (NaFl) staining patterns. If upper lid tuck is excessive, steepen the base curve and/or decrease the lens diameter. If a lens exhibits excessive movement with each blink, increase the diameter, steepen the base curve and/or reduce the edge lift. With GP lenses that decenter laterally, an increased diameter lens may improve centration. In cases of significant limbal-to-limbal astigmatism, toric peripheral curves help reduce excessive edge lift and peripheral bearing. The NaFl pattern indicating this shows excessive pooling at 12 o'clock and 6 o'clock and bearing at 3 o'clock and 9 o'clock. In cases where the NaFl pattern of a spherical lens shows excessive bearing along the horizontal meridian in with-the-rule (WTR) astigmatism or along the vertical meridian in against-the-rule (ATR) astigmatism, a bitoric GP will provide a more stable fit. Topographers with CL designing programs have simulated NaFl patterns that can illustrate this concept (figure 2).
With new and improved multifocal lens designs available, CLs can be a great option for baby boomers. Set yourself up for success by educating these patients on the benefits and limitations of multifocal lenses. Careful evaluation of a patient's eye dominance and pupil size is important to multifocal success. Both you and the patient must be aware of factors that may cause adverse conditions, such as very small or very large pupils, residual astigmatism and difficulty with depth perception prior to fitting. Current GP wearers may transition well into multifocal GPs because they are already conditioned to GP wear. However, proceed with caution in patients who have tight upper lids, very small or large pupils and high add powers. These CLs must translate properly so the patient can experience both distance and near zones. No-line multifocal GPs have a highly aspheric back surface and as a result, may induce spectacle blur with high add powers. Many new lens designs incorporate additional add power onto the peripheral anterior lens surface rather than increasing the back surface asphericity. A hybrid multifocal, consisting of a spherical distance GP lens with a center front surface near addition, may exhibit minimal movement.
Figure 3: topography map of post-surgical oblate cornea.
If the patient has or you suspect keratoconus, pellucid marginal degeneration (PMD) or irregular astigmatism, perform topography to confirm the diagnosis prior to attempting a CL fitting. This allows you to explain the condition as well as describe preferred CL options to the patient at the initial visit. It's prudent to ensure that the patient is aware of his condition and willing to proceed with the necessary CLs. If he wants to proceed, schedule the specialty fit during an advantageous time in your schedule. Avoid peak times, such as evenings and weekends, as you won't have enough time to spend with these special patients. If you don't own a topographer, can't invest in multiple fitting sets and/or aren't comfortable fitting these cases, refer them to an O.D. who specializes in keratoconus and post-surgical fits. The National Keratoconus Foundation (phone  521-2524) maintains a referral list to help you direct your patients to the nearest specialty lens fitter.
Post-refractive surgical and post-penetrating keratoplasty (PKP) cases can be some of the most challenging CL fits. Many of these patients have had multiple surgeries and experience poor vision with spectacles. Topographies may reveal highly irregular astigmatism, ectasia or extremely oblate profiles. Traditional spherical soft or GP lenses rarely work due mainly to the aberrations induced from the surgical procedure. Rigid lens optics will allow you to overcome many of the aberrations by vaulting the central irregularity. However, you must match the peripheral fit as well. Reverse geometry CLs allow for a flat central base curve followed by a steep reverse curve. Most GP labs can design a reverse geometry lens for you based on the topography map. Check with your lab of choice for the recommended fitting method. Consider referring postsurgical patients to a specialty lens fitter if you're not set up for the challenge. (Figures 3, 4, 5.)
Figure 4: topography map of Post-LASIK ectasia.
Figure 5: topography map of post-PKP irregular astigmatism.
Figure 6: An acceptable scleral edge profile shows no conjunctival vessel blanching.
Beyond the cornea
Fitting hybrid and scleral lenses requires inherent knowledge of corneal sagittal height. And achieving the proper lens-to-cornea relationship in the periphery is an important factor in maintaining comfort and optimum corneal health with these special lens designs. Contributing factors are the apical radius of the cornea (Ro), HVID and the chord length of the lens you fit. If the peripheral fit isn't correct, the lens will be too uncomfortable to wear. A tight periphery will cause blanching of the scleral vessels with subsequent redness and irritation (See figure 6). Modifications to scleral lenses include increasing or decreasing the edge lift as well as incorporating toric peripheral curves. With hybrid lenses, you can order a flat skirt curve to loosen the edge of a tight lens or a steep skirt curve to tighten the edge of a loose lens.
By incorporating the aforementioned CL-fitting pearls into your practice, you may create a following of very satisfied, loyal patients. What could be better? OM
||Dr. Anderson practices in suburban Chicago, specializing in orthokeratology, keratoconus and post-surgical lens fits and anterior segment disease. E-mail her at dianne.ander firstname.lastname@example.org.|
Optometric Management, Issue: June 2008