Article

THE CONTINUUM OF CARE FOR KERATOCONUS

From spectacles to contact lenses to surgery, what care is most beneficial at each stage of this progressive disease?

It wasn’t that long ago that the options for keratoconus management included only small-diameter rigid lenses and, in 10% to 22% percent of cases, a penetrating keratoplasty.1-8 Today, we have a broad and ever-increasing number of viable options including larger-diameter intralimbal corneal GPs, scleral lenses, hybrid lenses, and custom soft lenses.

In addition, keratoplasty procedures have improved, and the recent U.S. Food and Drug Administration (FDA) approval of corneal cross-linking (CXL) provides an option that may slow or halt progression of the disease. The benefits and increasing popularity of new and more comfortable contact lens designs, combined with CXL’s effect on progression, should continue to reduce the number of individuals needing some form of keratoplasty procedure.

This article will discuss the current management options for keratoconus and will present a continuum of care with recommended options for the many different types of patients who exhibit this corneal disease.

PREVALENCE

Traditionally, the prevalence of keratoconus was believed to be 1 in 2,000.4 However, this was based on a registration study conducted from 1935 to 1982, and the diagnosis was based upon detection of scissors reflex with retinoscopy and keratometry outcomes. Of course, the introduction, increasing popularity, and constantly improving sophistication of corneal topography and pachymetry instrumentation allows for more substantive diagnosis of keratoconus.9 Recently, a Netherlands-based study that evaluated the records of 4.4 million patients from a mandatory health insurance database concluded that the prevalence of keratoconus in the general population was 1 in 375, or more than five times greater than previously reported.10 With the higher number of keratoconus patients in our practices today, it is increasingly important to customize the specific management regimen to each individual patient’s stage of disease.

KERATOCONUS EVALUATION

Corneal topography evaluation has played an important role in diagnosing individuals who have keratoconus who may not have been diagnosed using only keratometry. According to the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) study topography assessment group, four types of “cones” have been identified with the following frequencies:11

  1. Central “nipple” cone (28.7%)
  2. Oval (intermediate size) cone (44.3%)
  3. Globoid (large-diameter) cone (6.7%)
  4. Marginal (inferiorly displaced) cone (5.6%)

There have been several classification schemes for describing the various stages of keratoconus.12-14 None of these classifications systems are complete in terms of modern-day diagnostic tools, so our nomogram on p. 28 presents a combination of the systems. This classification system will be used in this article as a foundation for selecting the appropriate management options for a specified severity level of the disease condition.

PARADIGM SHIFT: CORNEAL CROSS-LINKING

Early detection of keratoconus has become even more important with the recent FDA approval of CXL. CXL is a medical procedure that combines the use of ultraviolet (UV) light and riboflavin (vitamin B2) drops. The absorption of UV-A light by riboflavin and singlet oxygen15 creates new corneal collagen cross-links, which shortens and thickens the collage fibrils, leading to stiffening of the cornea.16 CXL has demonstrated an ability to strengthen the cornea and—to a variable extent—to resist the progression of this ectatic disease, stabilizing the cornea.17

CXL should be recommended to keratoconus patients who have either demonstrated definitive progression or who are at high risk for progression. New diagnostic technologies are allowing eyecare professionals to diagnose keratoconus earlier and to detect progression earlier in established cases. The challenge is to be able to make these technologies available and affordable to primary eyecare providers.

MANAGEMENT WITH SPECTACLES

Spectacle correction has very limited use in keratoconus due to the increasing corneal irregularity as the disease progresses. That said, spectacles can provide adequate vision in patients whose keratoconus is very mild and whose astigmatism is more regular. Spectacles are particularly beneficial for such patients when their keratoconus does not appear to be progressing and/or they are reluctant to move into contact lenses.

CONTACT LENS MANAGEMENT

Contact lenses are still the primary vision correction modality in the management of keratoconus. The three keys to contact lens success are vision, comfort, and physiological response. The general principles in keratoconus contact lens fitting include:

  1. Avoid mechanical pressure on the corneal apex.
  2. Avoid hypoxic corneal stress.
  3. Maximize comfort through design.
  4. Optimize vision through design.

A number of contact lens management options are available today. These include standard soft lenses, custom keratoconus soft lenses, small-diameter and intralimbal corneal GP lenses, piggyback and recess systems, hybrid lenses, scleral GP lenses, and impression-based scleral lenses. The next several sections will discuss each of these options individually, including an overview, when to choose each lens type, pros and cons, and which patients are the best candidates for each option.

STANDARD SOFT LENSES

Similar to spectacles, standard soft lenses, typically soft torics, have very limited application in keratoconus. Their best application is in very mild cases due to their inability to create a tear lens to correct astigmatism and in their limited parameters for patients who become increasingly astigmatic, often with an oblique axis. Therefore, in cases in which there is minimal optical distortion and in which adequate vision is achieved with glasses, this is a viable option.

The benefits of standard soft lenses, when applicable, include comfort, centration, and corneal protection. The limitations include vision (as indicated above), dehydration, the potential for microbial contamination, and increased affinity for protein and lipid deposits that can result in giant papillary conjunctivitis in patients who already have allergy-prone eyes.

Other highlights include:

  • Spin-cast (mass-produced) soft toric lenses are readily available and marketed by the four major U.S. contact lens manufacturers as well as by smaller companies.
  • Trial lenses are available in almost all eyecare practices that prescribe contact lenses.
  • Most practitioners have expertise in fitting soft toric contact lenses.

When to Choose This Lens Standard soft torics are a good option for patients who do not have critical vision needs and who do not desire to wear glasses.

Pros:

  • Easy to fit.
  • Trial lenses readily available.
  • Relatively inexpensive.
  • Daily, monthly, or two-week replacement.

Cons:

  • Does not correct irregular astigmatism.
  • Rotational instability when the cornea is irregular.
  • Keratoconus patients are prone to contact lens papillary conjunctivitis due to ocular allergies and eye rubbing. Monthly and two-week replacement soft torics tend to attract deposits.

Ideal Patient Types and Patient Parameters:

  • Patients who have very mild keratoconus and regular astigmatism.

CUSTOM SOFT LENSES

An increasing number of lathe-cut custom soft lenses have indications for keratoconus correction. Some of these designs are available in a silicone hydrogel lens material, and there are companies that also lathe custom hydrogel lenses. Custom soft lenses offer the benefits of initial comfort and centration, and they can be manufactured in virtually any parameter, including steep base curve radii and almost any conceivable sphere power, cylinder power, and axis.

For oblate corneal topographies, there are reverse geometry custom soft lenses as well. These designs have a relatively flatter base curve radius compared to the secondary curve. This allows the lens to align with the central section of an oblate cornea, which is more common in post-refractive surgery and post-keratoplasty patients than in keratoconus.

Other highlights include:

  • Custom soft lenses are made-to-order and are designed empirically using Ks and refraction.
  • Most practitioners have some expertise with custom soft torics, but they may have less familiarity, as these lenses are less commonly fit.

When to Choose This Lens This option is best for the mild cases in which the amount of toricity is not extremely high or oblique, notably in patients who exhibit comfort and/or centration-related issues with corneal GP lenses, patients who are not interested in GP lens wear, or in patients who are GP intolerant.

Pros:

  • Ultimate customizability in material, base curve, diameter, power, cylinder, and axis correction.
  • Good comfort compared to corneal GPs.
  • Good centration.

Cons:

  • With ultimate customizability, there may be too many parameters to change, which could result in many visits with variable results.
  • Less frequent replacement.
  • Comfort can be reduced with lathe-cut lenses.

Ideal Patient Types and Patient Parameters:

  • Early keratoconus.
  • Mild irregular astigmatism.

KERATOCONUS-DESIGN THICK SOFT LENSES

More recently, some companies have developed very thick soft lenses to mimic the properties of GP lenses for keratoconic eyes (Figure 1). The thickness of these lenses allows them to mask a small amount of corneal irregularity, and they provide comfort that is similar to soft lenses. They are often quarterly replacement lenses with relatively low oxygen transmission.18 However, with the greater thickness centrally—and if a hydrogel material is used—hypoxia-related complications are possible. Likewise, inflammation and infection concerns are possible as well.

Figure 1. A keratoconus-design custom soft lens. The central portion is steep and also represents the thickest area of the lens, whereas the outer section is much flatter in curvature.

When to Choose This Lens This is an option for early keratoconus patients, especially those who do not wish to wear GP lenses. They should be monitored for tight lens syndrome and corneal hypoxia.

Pros:

  • Good comfort.
  • Fitting familiarity/ease of soft lenses.

Cons:

  • Vision not as good as with GP lenses.
  • Low oxygen transmission.
  • Higher cost compared to some other options.
  • Tight lens syndrome can result.

Ideal Patient Types and Patient Parameters:

  • Patients who have mild keratoconus.
  • Patients intolerant to corneal GP lenses.

CORNEAL GP LENSES

Corneal GP lenses were the mainstay for keratoconus management for decades. Recent developments with scleral and hybrid lens designs resulting in better initial comfort and stability have relegated corneal designs to a secondary status. That said, respondents of a recent survey indicated that 35.4% fit corneal (including intralimbal) GP lenses to greater than 50% of their keratoconus patients, which was second only to scleral lenses at 50.8%.19

When fitting corneal GP designs that are less than 11mm in diameter—often 8.5mm to 9.5mm—it is important to avoid apical bearing. At the conclusion of the eight-year CLEK study, 31% of patients who wore flat-fitting lenses that exhibited apical touch developed corneal scarring, whereas only 9% of the patients who were fit steep and exhibited apical clearance developed scarring.20 Along with lens discomfort, flatter fits were associated with an increased likelihood of penetrating keratoplasty.21 Therefore, it is important to vault the apex of the cone as well as to match the periphery of the cornea. Because of this, small-diameter lenses are typically best suited for relatively well-centered, “nipple” cone patients.22 Every laboratory has one (or more) small-diameter lens design for keratoconus.

Larger and/or decentered cones require medium-diameter corneal designs (i.e., overall diameter > 9.2mm and < 11mm) or larger-diameter lenses. Intralimbal GP lenses are larger corneal designs with overall diameters ranging from 11.0mm to 12.2mm (the most common diameter is 11.2mm). These are indicated for oval cones and are an option to initially consider in decentered cones and pellucid marginal degeneration. The fitting principles are similar to small-diameter designs in terms of the lens-to-cornea fitting relationship and good peripheral clearance. The first diagnostic lens is often recommended to be equal to the average K reading + 2mm (close to the steep K reading) or to the corneal topography value approximately 4mm temporal to center. As with smaller lenses, the dual goal is either mild apical clearance or very mild apical touch (i.e., “three-point touch”) and definite peripheral clearance. With both smaller-diameter and intralimbal designs, there is often the option of tucking the lower lens edge in toward the cornea when it is lifting off excessively.

Corneal GP lens design fitting can be easier and more successful via corneal topography fitting software. Corneal topographers that have GP lens design software use the topography information to develop the “best fit design,” while also allowing practitioners to manipulate the design parameters and see changes to the predicted fitting relationship if desired. A simulated fluorescein pattern and a full corneal analysis of the predicted lens-to-cornea fitting relationship is produced, and the vault in microns at any point behind the lens can be determined (Figure 2). Oftentimes, this information can be e-linked to the fabricating laboratory.

Figure 2. Simulated fluorescein pattern of a corneal GP lens via empirical design topography-based software.

When to Choose This Lens Many patients who have keratoconus are habituated to using GP lenses for vision correction. For those who are, many are happy with this strategy. Consistent monitoring is the key to ensuring proper corneal health in the short and long term.

Pros:

  • A high degree of precision can be built into the fit and the optics.
  • When fit well, corneal GPs are very safe and are effective at providing excellent vision, above what glasses or soft contact lenses can provide.
  • Relatively inexpensive.
  • A long-time, well-established, successful option.

Cons:

  • Corneal GPs require expertise to fit.
  • Comfort is always a challenge, as it is difficult for a spherical corneal lens to align with an irregular cornea that often has great asymmetry from quadrant to quadrant, so the lid-to-lens edge sensation can be a challenge. Likewise, any debris under the lens can cause momentary discomfort.
  • Inferior decentration is more likely, especially if the corneal apex is decentered.
  • Corneal GP lenses rest on the cornea and have the potential to touch the apex of the cone; central touch is associated with increased risk of corneal scarring.23

Ideal Patient Types and Patient Parameters:

  • Patients who have mild keratoconus.
  • Habitual GP wearers.
  • Patients who have scleral elevations, such as pingueculae or glaucoma filtering blebs.

PIGGYBACK LENS SYSTEMS

Sometimes a soft lens or a corneal GP lens alone will not provide adequate vision or comfort. In such cases, combining the two modalities through the use of either piggyback lens systems or hybrid lenses can achieve success.

Today’s piggyback lens systems typically consist of hyper-Dk frequent replacement soft lenses in combination with a hyper-Dk GP lens. This is important to meet the recommended tear oxygen tension to minimize or preferably eliminate corneal hypoxia.24 Often, a very low-powered (i.e., –0.25D to –0.50D) hyper-Dk silicone hydrogel lens is placed under the GP lens in an effort to solve the problem. A low-powered lens is used because the effective power of a soft lens placed in between the tear film and a GP lens is equal to, on average, 20% to 25% of the labeled power of the lens.25 However, a moderate plus-powered (i.e., approximately +6.00D) soft lens with a thicker center can be beneficial in patients who have an inferior apex, for which a GP lens will tend to decenter inferiorly.27

There are also recessed lens combinations in which a soft lens has a recessed or cutout region centrally such that a GP can fit into this space (Figure 3). As with a conventional piggyback system, recessed lens combinations have the benefits of comfort and centration; however, the latter is especially optimized as the GP lens sits within the anterior surface recessed area.

Figure 3. A recessed piggyback design.

When to Choose This Lens These systems are most often used today when a GP lens alone either does not center well on the cornea or the patient experiences some lens awareness.

Pros:

  • Relatively simple to fit, as the GP lens typically does not need to be changed when placed over a soft lens.
  • Improved comfort and centration over GPs alone.

Cons:

  • Added expense of extra lenses and their care when a frequent replacement lens is used.
  • More time needed for application, removal, and lens care.
  • Lower oxygen transmission.
  • When wearing a dual-lens system, it is important to apply the GP lens with a solution that is compatible with soft lenses.

Ideal Patient Types and Patient Parameters:

  • Patients who have decentered cones.
  • Patients intolerant to corneal GP lenses.

HYBRID LENSES

Hybrid contact lenses have a GP center bonded to a soft skirt. They are now available in higher oxygen permeabilities and with multiple skirt curves to help vault the ectatic cornea. Of the most recent generation of hybrid lenses, two are designed specifically for vaulting the apex of the cone in keratoconus. The lens vault benefits vision correction because the irregularity of the corneal shape is neutralized by the tear fluid.

Apical clearance is important with hybrid lenses; a 100-micron clearance at dispensing (Figures 4 and 5) is recommended, as the lens may settle 30 to 60 microns. Lenses that become tight and uncomfortable after two to three hours have too much vault.

Figure 4. Optimal 100-micron central clearance of a hybrid lens on a keratoconic eye. The sodium fluorescein pattern is even throughout the central portion of the lens, and there is feather touch inside the junction of GP and soft as the GP portion lands on the peripheral cornea. Also visible is edge lift of the GP portion and bearing of the soft skirt more peripherally.

Figure 5. Optimal 100-micron central clearance of a hybrid lens shown on anterior segment optical coherence tomography. A caliper bar indicates the vault above the corneal surface after 20 minutes of settling time.

Some patients will complain of fluctuating vision and/or comfort problems that do not sound like a vault problem, such as the lenses are comfortable on some days but uncomfortable on others. If a patient (or office staff) is applying the lenses too forcefully by pushing them onto the eye, excessive fluid will be forced from the bowl of the lens, and a vacuum will be created in the post-lens tear reservoir. This will, in turn, pull the lens too tightly onto the cornea and will force the inner landing zone to indent the cornea. You can remedy this problem by teaching patients to release their eyelids after lens approach to pull the lens onto the cornea during application. This “gentle” application technique prevents the vacuum of fluid, and the visual fluctuations and comfort problems should stop.

When to Choose This Lens Keratoconus patients experiencing either comfort or centration problems with corneal GP lenses, vision problems with soft contact lenses, a less-than-optimum experience with piggyback lenses, or complications with scleral lens wear are often good candidates for hybrid contact lenses. With experience, the ease of fit, comfort, and stable vision can make hybrids a viable first-line treatment for some keratoconus patients.

Pros:

  • When fit well, the soft skirt provides comfort that is more in line with soft lenses than with corneal GP lenses.
  • The soft skirt helps improve centration, allowing consistent optics.
  • The back surface of the GP portion of the lens has a reverse geometry design, so when fit well the lens does not contact the apex of the cornea. This would eliminate any risk of corneal staining or scarring associated with apical bearing.
  • Fewer visits typically required for an optimal fit compared with scleral lenses. Fitting hybrid lenses for keratoconus requires a diagnostic evaluation with trial lenses. In most cases, a hybrid lens can be fit properly within three to four visits. In some cases, patients may leave with the initial lens ordered. This primarily depends on the complexity of the corneal irregularity and the skill of the evaluating practitioner.

Cons:

  • Only certain lens parameters are available. If eyes fall outside of, or even within, two lens parameters, the lens may not work properly.
  • There is potential for a tight-fitting lens, potentially resulting in lens awareness and vascularization. With the current generation of lenses, tight lens syndrome has been reduced, except when practitioners fit lenses with excessive vault.
  • Fewer practitioners are familiar with the nuances of fitting, evaluating, and troubleshooting these more recent hybrid designs.
  • As with scleral and custom soft lenses, the expense of a hybrid lens specifically for keratoconus is much higher compared to other types of lenses.

Ideal Patient Types and Patient Parameters:

  • Patients who have mild-to-moderate keratoconus.
  • Those who have comfort complaints with corneal GP designs.
  • Those requesting better vision than what they can achieve with soft toric lenses.
  • Newly diagnosed keratocones.

SCLERAL LENSES

When keratoconus becomes moderate-to-severe in stage, our preference is a scleral lens. Scleral lenses are very large-diameter GP lenses that do not contact the cornea. Rather, their weight is distributed over a broad area on the relatively insensitive sclera. For this reason, they tend to be a very safe and effective means of vision correction for patients who have keratoconus, and they provide comfort that is often superior to other contact lens options.

The vaulting fit creates a tear reservoir behind the lens and in front of the cornea that acts as a fluid bath for the cornea. Patients often indicate that dryness symptoms are much better with scleral lenses, and sclerals can provide relief for patients who have extreme dry eye that is not mitigated with other management options.

Scleral lens fitters have control over every curvature value in the lens, allowing for greater precision compared with other designs. Nearly any parameter can be manufactured, including toric front surfaces to correct internal astigmatism, notching to avoid elevated areas on the eye, and even multifocal optics. The broad range of parameters allows even highly irregular eyes to be fitted successfully.

Perhaps the most significant challenge to scleral lens success is practitioner experience; scleral lenses are perhaps the most complicated contact lenses to fit. As a result, very few practitioners have a true understanding of the technology. Unfortunately, there are no shortcuts to practitioner experience in troubleshooting. One study indicates that about three to eight visits are typically required for a proper result with scleral lenses,27 but individual results may vary widely.

As a result of the high degree of expertise required, the number of visits, and the cost of materials, scleral lenses are typically more expensive compared to other forms of vision correction. However, many vision plans and medical insurances can help defray the cost of visits and materials.

When to Choose This Lens Scleral lenses are beneficial to patients who have moderate-to-severe keratoconus or severe keratoectasia. They are a good second-line option when patients fail with any of the more primary lens options. Scleral lenses should be considered for patients who are experiencing problems with dry eye or with extreme vault settling onto the apex of the cone with hybrid lenses.

Pros:

  • Superior comfort, as they do not contact the cornea at all and rest on the insensitive sclera.
  • The power of the tear reservoir in providing relief from dryness symptoms.
  • A high degree of precision, with control over all curvatures of the lens design.
  • The ultimate in customization: the sky’s the limit with what parameters can be manufactured.

Cons:

  • Complicated to fit and requires a great deal of practitioner experience.
  • More visits required for a proper fit.
  • Greater expense.
  • The size of scleral lenses makes them difficult to apply and remove, and filling solution is required.

Ideal Patient Types and Patient Parameters:

  • Reserved for moderate-to-severe keratoconus; this is also mandated by Eyemed guidelines for medically necessary contact lenses.
  • Patients who exhibit very low hysteresis and have vault settling problems with corneal lenses or hybrid lenses.

IMPRESSION-BASED SCLERAL LENSES

The recent availability of impression-based scleral lenses allows practitioners to achieve an optimum fit on even the most irregular corneas and challenging cases. A customized scleral prosthetic is generated through the use of an impression taken of the front surface of the eye, similar to those taken for orthodontia. The impression is sent to a laboratory, where a scan of it is input into a computer-assisted design (CAD) program. A scleral prosthetic is built from the CAD file and manufactured.

This is the ultimate in scleral technology. For those who have failed with traditional sclerals or for whom traditional sclerals are not an option, this technology can be sight-saving. Impression-based scleral lenses are available only in limited locations, but they can be the final option before surgical management in many patients.

When to Choose This Lens As the last line of contact lens therapy.

Pros:

  • Because the impression-based scleral prosthetic contours the shape of the eye exactly, there is no contact lens available that is more comfortable. This holds true even for patients who have elevations on the sclera, such as pingueculae and pterygiae.
  • The impression-based scleral prosthetics fit lock and key with the ocular shape, so they are rotationally stable. This allows extremely precise optics to be built into the lenses without having to worry about lens rotation.
  • The impression and fitting process is painless and very quick, and there is no need for revisions to the fit. Custom impression-based scleral prosthetics can typically be completed in two to three visits depending on the complexity of the eye.

Cons:

  • Cost: the reason why we do not fit everyone with this device is that, as with any new technology, the cost is much greater. This is not a process that is billable to insurances. That said, the modality is less expensive compared to some scleral designs.

Ideal Patient Types and Patient Parameters:

  • Patients who have extremely thin corneas and very advanced keratoconus.
  • Patients who have severe keratoconus and scleral elevations, such as pingueculae and glaucoma filtering blebs.

SURGICAL OPTIONS

Surgical intervention for keratoconus should be considered when other forms of visual rehabilitation have failed or would benefit from supplemental approaches.

Intrastromal Corneal Ring Segments Corneal ring segments have been used for keratoconus management since the early 2000s.28 The intended benefits of corneal ring segment implantation for keratoconus include creating a more prolate cornea, with the apex closer to the visual axis; flattening of the corneal apex; and a reduction of corneal irregularity. The functional outcomes desired include improved contact lens tolerance and possible use of less complex contact lens designs; some degree of improvement in the acceptance of spectacle correction by potential reduction of ametropia and anisometropia; and some degree of improvement in both uncorrected and best-spectacle-corrected visual acuities.

However, corneal ring segment implantation for keratoconus has had limited success and acceptance in the ophthalmic community. In some cases, eyes have become more challenging to fit with contact lenses following this surgery (especially when corneal GP lenses are used). Other complications that have been reported following corneal ring segment implantation are beyond the scope of this article.

Keratoplasty Corneal keratoplasty procedures are also an important option for the surgical management of keratoconus. Due to the morbidity issues associated with these procedures, they should be considered only when other options for vision improvement have been attempted and failed.

Procedures such as penetrating keratoplasty and deep anterior lamellar keratoplasty can be vision saving when applied in the appropriate cases. However, practitioners must help establish realistic expectations for their patients following these procedures. Specifically, they should be told that a significant percentage of patients will still require contact lenses following keratoplasty and that fitting lenses post-keratoplasty can be as challenging as fitting keratoconus. New technologies such as femtosecond-enabled keratoplasty have resulted in better and more predictable outcomes; however, serious postoperative risks still exist.

New Procedures Developing surgical technologies such as topography-guided laser corneal ablation are showing some degree of promise to sculpt the cornea in an effort to reduce the irregularity of the keratoconic corneal surface. Concerns still exist regarding the efficacy and predictability of these procedures, but we can expect improvements in outcomes as these technologies are further developed.

CONTINUUM OF CARE FOR KERATOCONUS NOMOGRAM*

Forme Fruste29 (Sub-clinical)

  • Topography shows eccentric steepening
  • Pachymetry is normal (500 microns or greater)
  • Myopia and astigmatism < 5.00D13
  • Mean central K < 48.00D
    Treatment Options:
    1. Spectacles
    2. Off-the-shelf or custom soft toric lenses
    3. Hybrid lenses

Mild

  • Topography shows inferior steepening
  • Pachymetry > two standard deviations from the normal 550 microns (< 500 microns)
  • Myopia and astigmatism 5.00D to 8.00D
  • Mean K ranges from 40.00D to 48.00D13
    Treatment Options:
    1. Keratoconus-design corneal GP lenses
    2. Hybrid lenses
    3. Keratoconus-design thick soft lenses

Moderate

  • Topography shows significant steepening
  • Mean K ranges from 48.00D to 52.00D13
  • Pachymetry 300 to 400 microns
    Treatment Options:
    1. Hybrid lenses
    2. Scleral lenses

Severe

  • Mean K > 52.00D30
  • Pachymetry 200 to 300 microns
    Treatment Options:
    1. Scleral lenses
    2. Impression-based scleral lenses

Surgical Keratoconus

  • CXL: pachymetry > 300 microns with evidence of progression
  • Intrastromal corneal ring segments: pachymetry > 250 microns in the corneal midperiphery
  • Keratoplasty: pachymetry < 200 microns, significant central scarring, refraction not measurable

* Adapted from Alió and Shabeyek13 and Amsler14

RESOURCES

There are many resources and organizations to assist in making your keratoconus patients succeed in whatever management option is selected for them:

  • The National Keratoconus Foundation (NKCF) (www.nkcf.org ) has a wealth of consumer resources, including videos, informational brochures, and Frequently Asked Questions (FAQs), as well as information for eyecare practitioners and a referral service.
  • The International Keratoconus Academy of Eye Care Professionals (IKA) (www.keratoconusacademy.com ) was recently established by prominent optometrists and ophthalmologists to promote ongoing professional education. The IKA has a number of resources including a blog for practitioners to gain experience in challenging cases from experts in the field.
  • The Gas Permeable Lens Institute (GPLI) (www.gpli.info ) has a number of resources under the Education/By Lens Type/Keratoconus tab. This includes approximately 25 archived webinars from the leading experts in the field and a four-lecture series. In addition, a Scleral Lens Troubleshooting FAQs Module (developed in cooperation with the Scleral Lens Education Society [SLS]) is available. There is also a module on coding and billing for specialty lens patients.
  • The SLS (www.sclerallens.org ) provides workshops all around the country. There are also a number of resources online including patient education videos on care and handling.
  • Laboratory consultants and laboratories’ websites provide many resources. Laboratory consultants can help with lens selection, fitting, and troubleshooting keratoconus lens fits, especially if provided with topography maps and, if possible, photos or video of the fitting relationship.

THE BOTTOM LINE

Staging the condition is the first step in making treatment decisions. We propose a nomogram for when to choose each management option based on the stage of disease (See sidebar above).

In general, for forme fruste keratoconus, spectacles, off-the-shelf soft torics, custom soft torics, and hybrid lenses can be successful. In mild stages, keratoconus-design corneal GPs, hybrids, piggyback lenses, and keratoconus thick soft lenses are optimal, in our experience. For moderate keratoconus, hybrid and scleral lenses are best. In severe stages, scleral and impression-based sclerals are best, or surgery. Of course, always remember that there will be exceptions to these choices, especially when extenuating circumstances occur such as corneal scarring or a peripherally decentered cone apex. CLS

REFERENCES

  1. Rabinowitz YS. Keratoconus. Surv Ophthalmol. 1998 Jan-Feb;42:297-319.
  2. Tuft SJ, Moodaley LC, Gregory WM, Davison CR, Buckley RJ. Prognostic factors for the progression of keratoconus. Ophthalmology. 1994 Mar;101:439-447.
  3. Mandell RB. Contemporary management of keratoconus. Int Contact Lens Clin. 1997 Mar-Apr;24:43-58.
  4. Kennedy RH, Bourne WM, Dyer JA. A 48-year clinical and epidemiologic study of keratoconus. Am J Ophthalmol. 1986 Mar 15;101:267-273.
  5. Zadnik K, Barr JT, Gordon MO, Edrington TB. Biomicroscopic signs and disease severity in keratoconus. Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study Group. Cornea. 1996 Mar;15:139-146.
  6. Eggink FAGJ, Pinckers AJLG, van Puyenbroek EP. Keratoconus, a retrospective study. Contact Lens J. 1988;16:204.
  7. Sayegh FN, Ehlers N, Farah I. Evaluation of penetrating keratoplasty in keratoconus. Nine years follow-up. Acta Ophthalmol (Copenh). 1988 Aug; 66:400-403.
  8. Smiddy WE, Hamburg TR, Kracher GP, Stark WJ. Keratoconus. Contact lens or keratoplasty? Ophthalmology. 1988 Apr;95:487-492.
  9. Eiden SB, Matz M. Keratoconus is more prevalent than we thought. Contact Lens Spectrum. 2017 Apr;32:14-15.
  10. Godefrooij DA, de Wit GA, Uiterwaal CS, Imhof SM, Wisse RP. Age-specific incidence and prevalence of keratoconus: a nationwide registration study. Am J Ophthalmol. 2017 Mar;175:169-172.
  11. McMahon T. CLEK topography assessment group. Presented at the Global Keratoconus Congress, Las Vegas, January, 2008.
  12. McMahon TT, Szczotka-Flynn L, Batt JT, et al. A new method of grading the severity of keratoconus: the Keratoconus Severity Score (KSS). Cornea. 2006 Aug;25:794-800.
  13. Alió JL, Shabeyek MH. Corneal higher order aberrations: a method to grade keratoconus. J Refract Surg. 2006 Jun;22:539-545.
  14. Amsler M. Kératocõne classique et kératocône fruste; arguments unitaires. Ophthalmologica. 1946 Feb-Mar;111:96-101. Undetermined Language.
  15. Kamaev P, Friedman MD, Sherr E, Muller D. Photochemical kinetics of corneal cross-linking with riboflavin. Invest Ophthalmol Vis Sci. 2012 Apr 30;53:2360-2367.
  16. Beshtawi IM, O’Donnell C, Radhakrishnan H. Biomechanical properties of corneal tissue after ultraviolet-A-riboflavin crosslinking. J Cataract Refract Surg. 2013 Mar;39:451-462.
  17. Raiskup-Wolf F, Hoyer A, Spoerl E, Pillunat LE. Collagen crosslinking with riboflavin and ultraviolet-A light in keratoconus: long-term results. J Cataract Refract Surg. 2008 May;34:796-801.
  18. Pelc C. Meeting the challenge. Optometric Management. 2012 Aug;47: 66, 71.
  19. Bennett ES. GP Annual Report 2017. Contact Lens Spectrum. 2017 Oct;32:22-25, 29-31.
  20. Zadnik K, Barr JT, Steger-May K, et al. Comparison of flat and steep rigid contact lens fitting methods in keratoconus. Optom Vis Sci. 2005 Dec;82:1014-1021.
  21. Gordon MO, Steger-May K, Szczotka-Flynn L, et al. Baseline factors predictive of incident penetrating keratoplasty in keratoconus. Am J Ophthalmol. 2006 Dec;142:923-930.
  22. Bennett ES, Barr JT, Szczotka-Flynn L. Keratoconus. In Bennett ES, Henry VA, Clinical Manual of Contact Lenses (4th ed.), Philadelphia, Lippincott Williams & Wilkins, 2014:518-577.
  23. Korb DR, Finnemore VM, Herman JP. Apical changes and scarring in keratoconus as related to contact lens fitting techniques. J Am Optom Assoc. 1982;53:199-205.
  24. Weissman B, Ye P. Calculated tear oxygen tension under contact lenses offering resistance in series: Piggyback and scleral lenses. Cont Lens Anterior Eye. 2006 Dec;29:231-237.
  25. Woo M, Weissman BA. Effective optics of piggyback soft contact lenses. Contact Lens Spectrum. 2011 Nov;26:50-52.
  26. Bennett ES, Grohe RM, Anderson BW, Lipson MJ, Szczotka-Flynn LB. Piggyback applications in modern contact lens practice. Contact Lens Spectrum. 2007 Dec;22:17.
  27. Pecego M, Barnett M, Mannis MJ, Durbin-Johnson B. Jupiter Scleral Lenses: the UC Davis Eye Center experience. Eye Contact Lens. 2012 May;38:179-182.
  28. Colin J, Cochener B, Savary G, Malet F. Correcting keratoconus with intracorneal rings. J Cataract Refract Surg. 2000 Aug;26:1117-1122.
  29. Saad A, Gatinel D. Topographic and tomographic properties of forme fruste keratoconus corneas. Invest Ophthalmol Vis Sci. 2010 Nov;51:5546-5555.
  30. Piñero DP, Alio JL, Barraquer RI, Michael R, Jiménez R. Corneal biomechanics, refraction, and corneal aberrometry in keratoconus: an integrated study. Invest Ophthalmol Vis Sci. 2010 Apr;51:1948-1955.