Managing Irregular Cornea Patients
This type of specialty lens fitting can be a worthwhile addition to any contact lens practice.
Dr. DeNaeyer is the clinical director for Arena Eye Surgeons in Columbus, Ohio, and a consultant to Visionary Optics, B+L, and Aciont. You can contact him at email@example.com.
By Gregory W. DeNaeyer, OD, FAAO
Prescribing a contact lens that restores functional vision to a patient who has corneal irregularity is one of the most satisfying aspects of contact lens fitting. New materials and designs have led to unprecedented success, which has increased the popularity of irregular cornea management. This article will review basic philosophy and management strategies to help decrease the learning curve for practitioners interested in this contact lens subspecialty.
Corneal irregularity is usually secondary to a number of causes including trauma, dystrophy, or surgical complication. The irregularity creates higher-order aberrations that are not correctable by glasses or standard soft contact lenses. Patients who have an irregular cornea may have significantly reduced best-corrected vision with refraction and may complain of polyopia. Typically, corneal irregularity is easily diagnosed with topography and is often characterized by dioptric asymmetry and non-orthogonal astigmatism. The industry standard is to fit these patients with a GP lens to mask front-surface irregularity. However, the relatively thicker centers of some specialty soft lenses prevent them from conforming to an irregular shape, which enables them to mask mild amounts of irregularity. Unfortunately, back-surface corneal irregularity, found in keratoconus patients, can’t be masked by a lens sitting on the front surface, and this may limit a patient’s vision potential (Negishi et al, 2007; Nakagawa et al, 2009).
There is some evidence that irregularity not inherently masked by a contact lens could be corrected by contact lenses that have custom higher-order aberration correction; however, in vivo lens translation and rotation could limit their potential (Sabesan et al, 2007; Marsack et al, 2007; and others, full list available at www.clspectrum.com/references.asp). Additionally, neural adaptation to longstanding higher-order aberrations may limit initial subjective visual improvement (Sabesan et al, 2010; Sabesan et al, 2009; Artal et al, 2004).
The first step to successfully managing a patient’s irregular cornea with a contact lens is to educate him about specialty lenses. Explain in easily understandable terms how a specialty lens will benefit his vision. He will be more accepting of the nuances that come with a specialty lens if he understands why he needs one. Review other aspects of wearing a specialty lens such as vision potential, time commitment, cost, and potential complications. If the patient has unrealistic expectations, he will never be satisfied—even if the result is what you would perceive as successful.
Topography and Tools
A topographer is an important instrument for managing corneal irregularity. Topography lets you make or confirm a diagnosis, especially in the case of keratoconus. Secondly, corneal topography lets you gauge the severity of the irregularity, which helps when choosing a lens design. Lastly, topography lets you determine the overall shape of an irregular cornea, which helps in selecting lens design. For example, knowing that a cornea is severely oblate indicates considering a reverse geometry lens design.
One of the most important aspects of a successful fit is choosing the design that will maximize comfort and vision, won’t adversely affect the anterior surface, and that the patient can manage.
A key factor in choosing a lens modality is determining the severity of the patient’s corneal irregularity. Grading corneal irregularity can be difficult because variables contribute to severity, including steepness, asymmetry, and astigmatic orientation. Quantifying the irregularity is usually based on clinical experience. You can choose an initial lens design modality based on the relative amount of irregularity. Figure 1 shows a relative grading scale of corneal irregularity and modalities that will have the highest probability for success for each graded category. The scale is based on three premises. First, specialty soft lenses are somewhat limited to mild or moderate irregularity with regard to achieving acceptable visual acuity. Secondly, GPs become more forgiving with increasing diameter. Lastly, you should consider a design in the next category up if the initial lens needs excessive modifications for an acceptable fit.
|GRADE I - Least amount of corneal irregularity|
|■ Specialty soft lens design
■ Corneal GP or specialty corneal GP
|GRADE II||■ Specialty soft lens design fits with difficulty/vision compromise
■ Specialty corneal GP fits with difficulty
■ Corneal-scleral lens
■ Mini-scleral lens or hybrid lens
|■ Corneal-scleral lens fits with difficulty|
■ Mini-scleral or hybrid lens
■ Scleral lens
|GRADE IV - Greatest amount of corneal irregularity|
|■ Mini-scleral or hybrid lens fits with difficulty|
■ Scleral lens
Figure 1. Corneal Irregularity-Lens Modality scale.
Following the scale requires you to have several fitting sets to accommodate the spectrum of corneal irregularity. Because there is overlap in the scale, three different sets that span the scale should allow you to fit almost any cornea.
The grading scale is an initial guide. There are many other factors when choosing a particular design. For example, a patient who has moderate/severe keratoconus may prefer a specialty soft lens over a GP even though he may give up several lines of best corrected acuity as a consequence. Sorting out these variables in an efficient manner requires experience.
Ocular photography is an important tool for specialty lens fitting of irregular corneas. Photography is ideal for documenting diagnostic lens fits. Taking photographs of the anterior ocular surface before the lens fitting gives you a way to track any negative changes secondary to the lens system prescribed. Lastly, photographs of successful lens fits can be filed to document and track fitting changes.
Expensive stand-alone systems aren’t necessary, as standard digital cameras (Figure 2) used in conjunction with a slit lamp can provide outstanding results (see “Tips for Using a Digital Camera with a Slit Lamp” on page 34).
Figure 2. Position the camera at the slit lamp ocular.
Contact Lens Dispense
The dispensing visit for a specialty lens is a critical step for successfully managing an irregular cornea.
The goals for a successful dispense include determining that the patient has a reasonably fitting lens(es), determining that the patient has reasonable vision, instructing the patient on techniques for application and removal, educating and prescribing cleaning and disinfecting solutions, and educating the patient on safety issues and risks of lens wear.
If a careful diagnostic lens fitting was performed, the initial lens that is dispensed should fit reasonably well and provide expected visual acuity. This is especially true if the lens was ordered with standard design parameters. At this stage the lens does not have to be perfect, and making detailed changes too soon is not recommended because the fit of the lens can change during the adaptive process. However, don’t let the patient wear the lens if it poses a possible ocular health risk or if his vision is unacceptable.
Instruct patients on proper techniques for application and removal. Don’t assume that a patient knows how to do this even though he is a previous lens wearer. For example, transitioning patients from soft to GPs or from corneal GPs to sclerals will require detailed instruction and practice. Another training session may be needed to troubleshoot errors after he has had some experience with the lens.
Patients who have disabilities may require extra training time. Make sure to account for that when scheduling the lens dispense. If the patient has a primary caregiver, involve him in the process because he may be the one applying and removing the lens.
Instruct patients in detail on how to care for their lenses using prescribed care solutions. Be sure to ask whether they have previously experienced any hypersensitivities or toxicities to ophthalmic solutions.
Finally, educate patients about lens safety and risks. Remember that these patients are at risk for adverse advents just like any other contact lens patient. Consider giving patients a prepackaged bag for their supplies and a folder that reviews lens information (Figure 3). Follow up with patients within two weeks for reassessment. The frequency of additional contact lens checks will depend on each patient’s situation. If a patient is doing poorly without improvement after some initial changes, then consider refitting him into an alternate design. Usually this means refitting him in the next level up on the grading scale. Irregular corneas can change over time, especially in cases of keratoconus or corneal transplant. Significant corneal changes may necessitate modifications of the original fit or change in lens modality.
Figure 3. Send patients home with a folder and kit at their lens dispense.
Case Example #1
A 71-year-old patient who had penetrating keratoplasty of her left eye reported for contact lens reevaluation. Her best-corrected spectacle vision with her left eye after her corneal transplant was 20/200. The patient’s topography showed moderate irregularity with against-the-rule astigmatism. She previously had worn a specialty lens in her left eye to improve her vision, but had ultimately failed in a few designs. In an attempt to make application easier, an 11.2mm diameter GP specialty design was diagnostically fit. See Figure 4 for the best fitting diagnostic lens. The lens intermittently displaced from center, as might be expected from the fluorescein pattern. This lens could be improved by adding back-surface toricity, but this wouldn’t necessarily ensure lens stability.
Figure 4. Large-diameter GP contact lens on a cornea with against-the-rule astigmatism.
She was refit into a mini-scleral GP design with a diameter of 15.8mm (MSD, Blanchard) (Figure 5). This lens provided her with 20/20 vision and comfortable wear all day. Although the large-diameter corneal lens could have been modified, it would have taken significant effort and time. In this case, moving up a level with lens modality resulted in a successful first lens without modification.
Figure 5. A successfully fitting mini-scleral lens design.
Case Example #2
A 55-year-old keratoglobus patient reported for lens consultation. His right eye had a corneal transplant with recurrent keratoglobus. He had been wearing a corneal GP that provided 20/30 vision for his right eye, but complained of monocular “double vision.” Slit lamp examination showed the lens to be significantly decentered. The topographer was unable to produce a map of his eye secondary to the severity of his irregularity.
|Tips for Using a Digital Camera With a Slit Lamp|
|1 Take a picture of the patient’s chart and other pertinent information regarding the photograph. This will make it easier to sort pictures out after they’re downloaded.|
2 Use a high megapixel camera to maximize picture resolution. This is especially important for images that will be cropped to highlight specific sections.
3 Use back lighting (behind the patient) while turning down all other lights to reduce corneal reflections.
4 For slit photos, have an assistant direct light from a transilluminator onto the eye to reduce glare from the slit beam.
5 Attach a diffuser to your slit lamp that can temporarily be put up over the slit beam to photograph the sclera or for fluorescein shots.
6 Use a Wratten filter and the diffuser for fluorescein photographs of GP lenses.
7 Auto focus works great when using white light, while manual focus is best for fluorescein shots using cobalt light with a Wratten filter.
8 Take high definition video and then pick out still images to save.
The patient was refit into a full scleral lens (Jupiter Scleral, Visionary Optics) with a diameter of 18.4mm and a sagittal depth of 7.16mm (Figure 6). He reported doing significantly better with the scleral lens with great vision and all day lens comfort. Keratoglobus is by definition grade IV severity.
Figure 6. A full scleral lens on an eye with keratoglobus.
Case Example #3
A 28-year-old keratoconus patient reported for reevaluation because he did not like the comfort of his right scleral lens, although it provided 20/20 vision. Updated topography showed moderate/severe oval keratoconus. He was refit into a soft keratoconus lens design (Kerasoft, Art Optical).
Although the patient’s best vision in the right eye decreased to 20/40, his lens tolerance was significantly improved. In this case the patient’s wearing experience improved by dropping back to a specialty soft lens at the cost of several lines of acuity.
Irregular corneal fitting is an important and underserved niche and can be a worthwhile addition to any contact lens practice, as it can increase satisfaction and revenue.
The learning curve for mastering these specialty contact lens designs can be lessened by attending workshops that are found at most major meetings or that are offered by individual contact lens manufacturers. CLS
For references, please visit www.clspectrum.com/references. asp and click on document #197.