Profilometry/corneoscleral mapping is an exciting advancement in GP lens fitting. However, this and other highly advanced technologies used in the fitting and design of customized lenses come with a price for practices and patients. Specialty lens fitting can still be accomplished with little initial investment, and dedicated practitioners can help patients afford services outside of their reach.
Working with Less
Regular corneas can be fit with corneal GPs, hybrids, and/or specialty soft lenses using “normal” topography or keratometry, whether utilizing a fitting set or via empirical design. It is helpful to measure corneal diameter as well, and this can still be done effectively using horizontal visible iris diameter (HVID) and a handheld pupil diameter (PD) ruler. In particular, corneal GP lenses can correct many refractive conditions at low relative cost to both practice and patient.
Irregular corneas are far easier to fit with corneal GPs when topography is available, and topography is virtually indispensable when considering orthokeratology. It is possible to fit some irregular corneas from only a fitting set, though this can be very time consuming; rarely, if you are unable to obtain a reliable topographic image (i.e., due to severe ocular surface disease, poor patient cooperation, nystagmus, etc.), use of a fitting set may be the only option.
When sclerals are desired, performing corneal topography is ideal but not always necessary. In the absence of corneoscleral topography, comparing HVID and vertical visible iris diameter (VVID) can help differentiate patients requiring a more customized scleral design if a significant ellipsoid shape is found. High amounts of regular cylinder on corneal topography may correlate with scleral toricity (Consejo and Rozema, 2018; Macedo-de-Araújo et al, 2019) and necessitate more toric scleral landing zones. A scleral fitting set is required, but it is possible to obtain a loaner set from many manufacturers. Purchase a fit set if scleral fitting is to be continued; the cost may be offset by discounts on subsequent orders.
Working with less preliminary data makes properly assessing lens fit on patients’ eyes even more critical. Vital dyes such as fluorescein and lissamine green are relatively inexpensive and can be used to assess lens fit and tear flow as well as to monitor for corneal and conjunctival staining (Fadel, 2020) (Figure 1). When needed, lab consultants can provide feedback and support. Ultimately, if a fit is not progressing well, it may become necessary to refer patients to a colleague who has the equipment required to obtain the best lens fit.
Though new technology and advances in lens design are certainly intriguing and will help difficult-to-fit patients, a practitioner interested in specialty lens fitting need not feel overwhelmed or disadvantaged by a lack of early adoption. CLS
For references, please visit www.clspectrum.com/references and click on document #307.