Keratoconus – FAQ 1

What Design Should I Use for My Keratoconic Patient?

Background

The design to be selected for a keratoconic patient depends in large part on such factors as how much it has progressed (to include steepening and elevation of the apex of the cone), the size and location of the apex, and his or her past experiences with contact lens wear.

Several tools are available for practitioners today to manage keratoconus, including small-diameter GP lenses (often 8-9mm), intralimbal GP lenses (approximately 11mm), several forms of scleral designs (usually 14-18mm), hybrid lenses, and piggyback combinations.

While a corneal topographer is not mandatory in the fitting of a keratoconus patient, it is very beneficial in both the diagnosis (very likely if the steepest area, or apex, is ≥ 48D) and management of this patient. An anterior segment OCT is very helpful in determining the apical clearance, limbal vault, and lens edge relationship when fitting all forms of scleral lenses.

Management

Today there is a trend away from small-diameter lenses, which can often be displaced and lost. In addition, the resulting lens movement, possible decentration, and less than optimum alignment with an irregular cornea can result in lens awareness. As a rule of thumb, the larger the lens, the more comfortable it will be.

Intralimbal lenses appear to be the most common lens design of choice today; however, notably in the advanced cases, some form of scleral lens is becomingly increasingly popular. The selection of design can be based either on the corneal topography map or simply on whether the patient’s keratoconus is mild (apex is < 50D and absence of to minimal slit lamp signs), moderate (apex is 50-56D with slit lamp signs and possibly mild scarring), or severe (apex is > 56D with slit lamp signs often accompanied by scarring).

As with any challenging patient, consultation with your laboratory consultant can be invaluable toward the eventual success of your patient. If corneal topography maps and/or photographs or video of the fluorescein pattern of a lens on the eye are available to provide the consultant, that would be valuable as well.

When choosing a new lens for an existing GP lens wearer, unless there are major problems, be slow in making major changes to the lens design. If a patient is successful with a certain lens design, but is having only minor problems, try to improve or fine-tune the current fit as opposed to starting over. Build on the patient’s current success, and try to fix what may be causing the problem.

Analyze the fit of the lens in at least three zones. Evaluate the central area or base curve for heavy bearing or rubbing. Check the intermediate curves for proper lens support and the lens edge for proper clearance.

Severity of Keratoconus

  • Mild keratoconus. Custom soft lenses can be used in some of these cases, as well as small and intralimbal GP designs.
  • Moderate keratoconus. An intralimbal design is often a good starting point with these patients. If good centration and/or comfort is not achieved, a scleral design, hybrid design, or piggyback system can be used.
  • Severe keratoconus. Once again, an intralimbal design can be used initially, but in these cases it is often necessary to go to a larger, more stable and comfortable design. Typically a scleral design will be successful, although hybrid and piggyback modalities are viable options as well.

Corneal Topography

  • Small central (or paracentral) “nipple” cone. This type of pattern is observed in more than 25 percent of keratoconic patients and can often be managed by a small-diameter keratoconic lens design.
  • Mid-sized “oval” cone. This is the most common pattern, which is larger than the nipple cone and may also be more paracentral in location. An intralimbal is often a good design for these cases. If good centration and/or comfort is not achieved, a scleral design, hybrid design, or piggyback system can be used.
  • Large “globus” cone. Although representing less than 10 percent of all keratoconus patients, a larger design (i.e., beginning with intralimbal and, if unsuccessful, using a scleral design) or a hybrid or piggyback combination can be used.
  • Inferior decentered “marginal” cone. As a GP lens will tend to position over the steepest region of the cornea, a small design would be contraindicated in this case. As with oval and globus cones, an intralimbal design can be attempted initially, but one of the other options (i.e., scleral, hybrid, or piggyback) would likely be needed to provide a stable fit and satisfactory vision.

Useful Resources

GP Lens Institute

Publications

Acknowledgements

GP Lens Institute Advisory Committee members: Bruce Anderson OD, Marlane Brown OD, Carmen Castellano OD, Walter Choate OD, S. Barry Eiden OD, John Laurent OD, PhD, Derek Louie, OD, MS, Joe Shovlin OD, Frank Weinstock MD, Bruce Williams OD.