How do I choose lenses for a keratoconic patient?
“First determine the type of irregularity: nipple cone, oval cone, globus cone, or pellucid marginal degeneration. Then decide on a type of special design you like. I have found a smaller diameter (8.0-9.9mm) corneal lens is best on steep, fairly centrally positioned nipple cones. All other irregularities do better with larger (10.4-11.6mm) diameter corneal designs. Scleral designs are an option as well.” (Al Vaske, Advanced Vision Technologies)
“Topography is the best tool for deciding what type of design to use on a keratoconic patient. If the apex of the cone is within the central 4mm of the cornea, a traditional smaller diameter corneal lens should work. If the apex is outside of that area, a large-diameter irregular cornea design will probably be more effective. If the cone is very advanced (greater than 62.00 diopters), you will probably want to consider a semi-scleral or scleral design. After a design type is chosen, trial fitting is the best way to actually fit a patient. That will minimize chair time and the number of visits to complete the fit in the long run. Make sure you schedule an appropriate amount of time for the fitting visit — at least an hour, as it may be necessary to try several lenses.” (Alika Mackley NCLE-AC, ABB Optical Group)
“Prolate designs work better on more central cones, and oblate designs work better on cones outside the central area. Work with your lab consultants, and they can guide you to the correct design.” (Eric Marshall, Visionary Optics)
“When considering GP corneal contact lenses, there is no doubt that keratoconic patients should have topography performed to identify the type and severity. Fitting consultants can quickly identify what type of corneal GP design will be best suited for that individual patient. Topography elevation maps can also help determine if the change in elevation across exceeds the limits that a corneal GP lens can handle and will require the use of a scleral lens design.” (Mike Johnson, Art Optical)
“There are many brand names of keratoconic lenses. They can all be customized for a specific patient. So the question isn’t which lens to use but how to customize the lens for your patient’s specific needs. This is where the consultant’s role is crucial. Given topography or trial fit information, the consultant can recommend diameter, vault, and quadrant-specific features, based on experience.” (John Belliveau, Visionary Contact Lens)
When should I use a quadrant-specific lens design?
“Quadrant-specific edge treatments are invaluable for best fitting. The most common problem is standoff at 6 o’clock. This will cause lenses to pop off and/or make for discomfort in the inferior area. Steepen that area to solve the problem. I also see touch at the superior area, which requires the 12 o’clock area to be flattened. 3 and 9 staining can be corrected by flattening the edge at those positions. We have had success with quadrant-specific base curve designs. Bitorics do not always align the cornea, so when they do not, Quad Sym BC designs are an option. Improved scleral designs with higher sagittal depth fitting have made Quad Sym BC designs less needed.” (Al Vaske, Advanced Vision Technologies)
“You should consider going to a quadrant-specific design when you see peripheral areas that are significantly asymmetrical. For instance, it is not uncommon to see superior impingement and excessive inferior standoff peripherally on pellucid marginal degeneration (PMD) patients. Utilizing quadrant-specific designs allows you to adjust specific areas of the peripheral fit of the lens by flattening only the superior peripheral area and steepening the inferior periphery.” (Alika Mackley NCLE-AC, ABB Optical Group)
“Anytime a rotationally symmetrical lens cannot provide an acceptable fit, consider a quadrant-specific modality. They can be made to self-orient without prism, almost always increase comfort, and can be marked for orientation evaluation.” (George Mera, TruForm Optics)
When should I use a piggyback design, and which lens materials should I use?
“You should utilize piggyback designs when lenses cannot be stabilized through adjustment of the rigid lens fit or when the patient is intolerant of the comfort of a corneal lens design. Often, if a patient is intolerant of comfort, if you provide them with a two- to four-week supply of daily disposable lenses you can get them through adaptation, and they may choose to continue wearing without the carrier lens. Personally, I am a big proponent of utilizing daily disposable lenses for piggyback systems. That eliminates consideration of patient compliance in cleaning with two different regimens and is generally healthier, in my opinion.” (Alika Mackley NCLE-AC, ABB Optical Group)
“With all of our designs available, we very seldom need to use a piggyback fit. In that instance we will take an already fitting lens and place it on a low-powered, thin, high Dk disposable soft lens.” (Jeff Birk, Essilor)
“Rigid lens intolerance and/or poor centration are indications for a piggyback fit.” (Joe Hanson, ABB Optical Group)
“A piggyback system can be quite useful for many patients suffering from either corneal irregularities or corneal disease. If possible, a daily disposable soft lens that is stable on the eye sometimes offers the easiest system for patients in that the soft lens is thrown away after each use. There is no issue with confusion about different solutions for soft and GP lenses. A high Dk material in both the soft lens selection as well as the GP will help with overall oxygen transmission.” (Keith Parker, Advanced Vision Technologies)
“Piggyback designs have become less significant with the advent of scleral designs, but they can still be a valuable asset to a practitioner. We use this design on highly irregular corneas when patients want the acuity of a GP lens but the comfort of a soft lens. Our unique piggyback design has a soft lens with a controllable center cut-out that holds the GP lens in place. This creates a smooth transition between the two lenses and centers the GP perfectly.” (Derrell James, X-Cel)
“Hybrid lenses are a wonderful alternative to piggyback designs. Soft skirts provide excellent centration and comfort, and patients appreciate needing only one lens cost and care system.” (Connie Adam, SynergEyes)