7 strategies for fitting keratoconus patients

I view treating keratoconic patients as “extreme optometry” because it challenges our ability to correct refractive error unlike any other eye condition. At its core, the treatment is quite simple-get a smooth, rigid surface on the eye to focus light-and indeed, gas permeable (GP) contact lenses have long been the mainstay for improving vision in these patients.

However, discomfort, handling concerns, and even our own clinical misconceptions can be barriers to successful treatment. In addition, the corneal distortion is often so pronounced that it can be difficult even to get a corneal GP lens to stay on the eye, and patient psychology and practice management issues only add to the challenge.

Related: Collagen corneal cross-linking for keratoconus

In my years of specialty practice with keratoconus patients, I have refined the following techniques, and I’d like to share that knowledge.

Try these seven strategies to improve your keratoconus contact lens prescribing and offer better outcomes to your patients. 

1. Refract smarter, not more

You should spend, at most, five minutes refracting both eyes, reserving the majority of chair time for discussing of potential contact lens treatments.

Related: Keratoconus, crosslinking, and the changing treatment model

I use the following tips to guide my own “smart” refraction technique:

• Before using the phoropter, evaluate the patient’s corneal topography and use a slit lamp to assess the magnitude of corneal distortion. Advanced disease with corneal scarring and Munson’s sign lets you know not to refract with 0.25 D steps but rather to start with a large dial that measures in increments of +3.00 D (or +4.00 D). From that point, ratchet down to the +1.50 D retinoscopy lens, then +0.75 D, and so forth, until you arrive at the threshold of just-noticeable difference.

• The ideal method for cylinder and axis determination is often a handheld Jackson Cross Cylinder (JCC), because the JCC that is attached to the phoropter frequently won’t provide a perceptible change to many with keratoconus. A manual phoropter, rather than a digital one, may give you greater ease of using a hand-held JCC and presenting large dioptric steps.

• Have the patient look through the pinhole to indicate to both you and the patient the level of visual improvement possible with rigid contact lens optics.

Refraction in keratoconus is primarily used to demonstrate the necessity of contact lenses, showing to a third-party payer that glasses alone are unlikely to correct vision satisfactorily. This understanding requires a shift in our thinking because we typically refract to prescribe glasses. 

It’s important to remember that the keratoconic eye is characterized by elevated higher-order aberrations due to the cornea, with numerous unusual, asymmetrical distortions. Using the components of sphere and cylinder does not yield the best approximation to cancel out all the optical aberrations. It can result in a soft refraction endpoint because the keratoconic patient cannot distinguish the presented lower-order refractive steps. Higher-order aberrations such as coma, which is usually relatively high in keratoconus, have a directional component, similar to the lower-order aberration of astigmatism.

Related: When do you diagnose keratoconus?

If you are prescribing glasses, consider delaying refraction until after the contact lenses are finalized in order to minimize spectacle blur. Scleral lenses with adequate vault seem less prone to inducing spectacle blur.

It’s helpful to use a rotationally symmetric (or round) refraction target in both normal and keratoconic patients. If you use a digital Snellen chart, you can simply have the patient look at a letter “O.” By comparison, a rotationally asymmetric letter “H,” with the vertical legs, may bias undercorrection of with-the-rule astigmatism and vertical coma.

2. Separate the initial visit

Be sure to see a new keratoconus patient for an initial visit before any diagnostic fitting visit. The initial encounter confirms that the patient does indeed have keratoconus.

I’ve had patients referred with presumed keratoconus masquerading as Salzmann’s nodular degeneration, Terrien’s marginal degeneration, and epithelial basement membrane dystrophy.

Related: Early diagnosis is the first step in effective keratoconus treatment

Additionally, you’ll want to establish the severity of the condition because severity will dictate the type of treatment you recommend, whether it be simply glasses and soft lenses, thick soft lenses, corneal GP, hybrid, scleral, or another modality, which in turn dictates the patient’s out-of-pocket costs. You need the data collected at the initial visit to submit to the patient’s vision plan in order to allow for the coverage and lens allowance for the contact lens prescribing visit.

Cost often can be an issue, with a patient’s first question upon being referred to a specialist “How much will it cost?” The answer, of course, varies widely according to the patient’s required treatment and the third-party payer, if any.

Simply instructing your staff to defer this question and schedule the patient in for an initial encounter lowers this barrier to care and prevents the possibility of a patient foregoing treatment entirely due to her concerns about out-of-pocket costs.

Many patients have misconceptions about the type of contact lenses required to treat keratoconus. The initial visit allows you to educate these patients that they are receiving a custom-caliber lens which requires additional time and attention.

Related: Keratoconus: cracking the corneal code

Another reason to separate the initial visit from the diagnostic fitting is to allow for the formation of a rapport with the patient. This is critical for a desirable outcome and allows you to set the patient’s expectations while tailoring your treatment according to her unique situation.

3. Think hybrids and sclerals

Hybrid and scleral contact lenses are increasingly prescribed as a first-line treatment for keratoconus. Hybrid lenses try to combine the vision quality of rigid lenses with the comfort and stability of soft lenses, and they are a reasonable treatment for many keratoconic patients. Scleral lenses vault the entire cornea, resting on the conjunctiva overlying the sclera, often providing exceptional comfort and vision.

In patients with pronounced corneal depth-the larger-diameter scleral lenses may be more appropriate that hybrid lenses. In fact, scleral lenses make up the fastest-growing part of my own irregular cornea practice.

Related: When do you diagnose keratoconus?

Thick soft contact lens designs and piggyback designs are typically last resorts for the treatment of keratoconus in my practice. The go-to contact lens design for keratoconus used to be corneal GP contact lenses. These lenses are still good options for keratoconic patients in whom maximal tear exchange is vital, such as patients with a history of contact lens acute red eye (CLARE) or marginal keratitis, or those with blepharospasm preventing application of larger diameter lenses.

No single lens design will work for every patient with keratoconus, however, because every case is so different-each keratoconic eye is different with respect to the magnitude and pattern of distortion, and the patient-specific factors of expectations and tolerability are unique as well.

 The latest hybrid contact lens for keratoconus, SynergEyes UltraHealth, combines a 130 Dk rigid center with an  84 Dk silicone hydrogel skirt.

Patients who may benefit from UltraHealth and scleral lenses include:

• Those with the irregular astigmatism, including keratoconus and post-LASIK ectasia

• Patients who are wearing corneal GP lenses but are having problems with working in dusty environments, lens ejection, and 3 and 9 o’clock corneal staining

• Some patients who use piggyback systems

Related: How corneal biomechanics affects keratoconus and ectasia

A defining factor with UltraHealth, as with scleral lenses, is vault, or the amount of lift from where the lens sits away from the corneal surface. With UltraHealth, lenses are available in vaults ranging from 50 μm to 550 μm.  Scleral lenses can accommodate an even greater magnitude of sagittal protrusion.

For an irregular cornea in which the corneal apex is off center and protruding, placing the UltraHealth lens or scleral lens on top creates a fluid reservoir that clears the irregular cornea even though the interior reservoir is not as large. Ideally, a final UltraHealth lens should provide at least 100 to 150 μm of clearance over the corneal apex. SynergEyes UltraHealth lenses have about a 200 μm thickness, which is useful as a benchmark for assessing the thickness of the post-lens tear film.  Scleral lenses also maintain a significant fluid reservoir, with many scleral lens prescribers targeting 250 to 350 μm central vault.

4. Use topical anesthetic

Using a topical anesthetic at diagnostic lens fitting is beneficial on many levels. It eliminates blepharospasm and enhances your ability to evaluate the fluorescein pattern without excessive tears confounding your observation. Topical anesthetic also improves the patient’s comfort and confidence, encouraging him or her to ascribe additional value to the contact lens and related services.

You should always apply and remove lenses personally to enhance speed and hygiene and minimize the possibility of error (such as bubbles or inadequate fluorescein).  The patient can learn how to apply and remove the lenses at the dispensing visit.

The diagnostic fitting is also an ideal time to remind the patient that the comfort and vision of the diagnostic lens are generally irrelevant-they simply provide measurements for the custom order. It should also be reinforced that contact lens prescribing is typically a process that spans several visits. Each diagnostic lens evaluated on the eye potentially saves the patient an additional visit, and communicating this to the patient can build value.  The end result of the prescribing process is that the patient will have the best-possible contact lenses.

Related: Ensuring patient success with contact lenses

5. Evaluate vault

With scleral lens prescribing, there has been much discussion among practitioners about using anterior segment optical coherence tomography (OCT) to determine vault. Although helpful, time constraints may limit the efficacy of this method.

I recommend using an optic section during biomicroscopy to compare the center thickness of the contact lens to quickly assess the depth of the post-lens tear film. The rule of thumb is to target for about half the thickness of the UltraHealth center for the post-lens tear film, and with scleral lenses, to target approximately the same thickness for the post-lens tear film.  The same technique of using an optic section is useful for assessing the peripheral vault.

If the lenses have excessive vault, especially scleral contact lenses, a common problem is accumulation in the tear interface of metabolic debris. After 30 minutes to several hours, patients may complain of milky or foggy vision. 

6. Try SCOR

If spherical over-refraction (SOR) is not improving vision to 20/20, perform a spherocylindrical over-refraction (SCOR) to look for residual astigmatism.

The residual astigmatism is generally due to lens flexure or the posterior toricity of the cornea, not the crystalline lens. Demonstrate the correction of residual astigmatism to patients with a handheld lens. Rotating the handheld lens over the contact lens can demonstrate to the patient why correcting this requires rotational stability and is often trickier to address. 

I have found that front surface toric corneal GP lenses often don’t work well due to rotational instability and greater lens awareness from increased lens mass. Front surface toric hybrid contact lenses are not currently available. With spherical corneal GP and hybrid contact lenses, you can to prescribe glasses for use on top of the patient’s contact lenses to address any significant residual astigmatism. Alternatively, I’m impressed by how well front surface toric optics work for scleral lenses.

Related: Using tinted contact lenses in practice

7. Go piggyback

There are instances with corneal GP and hybrid contact lenses in which there is still some mechanical interaction over the epithelium, which leads to patient discomfort and light sensitivity. The ultimate solution for many of these patients is to move them into scleral contact lenses, but often, a simpler solution and intermediate step is to prescribe a disposable soft contact lens underneath in order to protect the epithelium from the mechanical interaction.

I recommend a silicone hydrogel daily disposable contact lens. Regarding the correct power to use, a low minus power is preferable.¹ The lenses are applied separately, but removal, especially with a hybrid lens, is often combined.

However, if you wish to reduce the patient’s awareness of the GP lens edge, a soft disposable piggyback lens does not help. 

The one piggyback lens that does help reduce GP edge awareness is Flexlens Piggyback lens, a soft carrier lens with an anterior cutout which countersinks the GP lens underneath the surface.

That will reduce edge awareness, but I rarely use this lens design today with the availability of hybrid and scleral contact lenses.

Improve outcomes

By trying these strategies, you can expect more positive outcomes with your keratoconic patients.

Finally, in order to enhance your role as a true partner in your patients’ care, suggest they visit the website of the National Keratoconus Foundation. It offers keratoconus patients information, support, and advocacy and may improve their overall experience with this challenging and complex condition.

Read more in our Contact Lenses and Lens Care Resource Center

References:

1. Romero-Jiménez M, Santodomingo-Rubido J, González-Meijóme JM, Flores-Rodriguez P, Villa-Collar C. Which soft lens power is better for piggyback in keratoconus? Part II. Cont Lens Anterior Eye. 2015 Feb;38(1):48-53.