How do I choose lenses for a keratoconic patient?
“The design of choice for keratoconus depends on several factors. The size of the cone, location, severity and period of time the patient has been diagnosed with the disease are all important elements in determining the lens design that will provide the best fit, comfort, and acuity for the patient. Also, information on previous lens designs the patient has worn and success with those designs will be useful. If no information is available on lens history, a topography will provide the information necessary to choose the best design. If no topography or information is available, then a loaner fitting set is recommended as an alternate means of gathering the necessary information to fit the patient with the best design.” (Ann Shackelford, ABB-Concise)
“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, Lens Dynamics Corporation)
“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, Firestone Optics)
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, Lens Dynamics Corporation)
“You should consider going to a quadrant specific design when you see peripheral areas that are significantly assymetrical. 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, Firestone Optics)
“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. Oftentimes, 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, Firestone Optics)
“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, Mid-South Premier Ophthalmics)