Practitioners have been fitting hybrid lenses using only keratometric readings (Ks) and spectacle prescription (Rx) for years. But this year, fitting hybrids empirically takes on a whole new meaning. With COVID protocols in place, we know that guidelines for handling multipatient-use contact lenses, or diagnostic lens sets, must be strictly followed (American Academy of Optometry and American Optometric Association, 2019).
One year ago, I was invited to participate in an industry-sponsored roundtable discussion on the future of hybrid lens fitting. At that time, the COVID-19 crisis was in its infancy, and its widespread impact was minimal. Talks of fitting customized hybrid lenses on first-time wearers without placing a trial lens on eye stemmed mostly from the updated guidelines to the International Organization for Standardization (ISO) standards on the process of hygienic management of contact lens fit sets (ISO, 2018).
Is Technology a Must?
For the patient in Figure 1, who has an Rx of –0.50 –1.75 x 180 with near limbus-to-limbus astigmatism and complains of fluctuating vision with daily disposable soft toric lenses, providing K readings acquired from a keratometer or an autorefractor along with a spectacle refraction to a fitting consultant would be adequate to manufacture a new lens.
Additionally, horizontal visible iris diameter (HVID) helps with determining the most appropriate skirt curve of a hybrid lens. Some autorefractors measure HVID, but if not, a handheld ruler or corneal topographer can be used. It was proposed during the roundtable discussion that patients can hold a pupil diameter (PD) or HVID ruler against their eye while practitioners zoom in to clearly read the millimeter value and take a picture with a cell phone to confirm HVID (Figure 2).
Pupil size can be measured via PD reference cards or a PD ruler for empirical order of progressive hybrid lens fits (refractive add power would be required too).
Empirical fitting of hybrid lenses for irregular corneas (Figure 3) will require a few extra steps. A fitting consultant can take a normalized axial map and use local software to calculate the sagittal depth of a hybrid lens required to vault over the entire eye. For this reason, a corneal or corneoscleral topographer is required for empirical fitting of irregular corneas with vault/sagittal depth-based hybrids. A manifest refraction or GP refraction is useful, but not necessary, to determine hybrid lens power.
Say Goodbye to Hybrid Lens Diagnostic Sets
Because hybrid lenses need to be stored wet, time and resources are required to appropriately clean and disinfect reusable trial lenses in accordance with international standards. Skip this extra effort and embrace empirical fitting of today’s newest generation of hybrids. CLS
For references, please visit www.clspectrum.com/references and click on document #303.