Contact Lens Spectrum Supplements

Special Edition 2017

Contact Lens Spectrum

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C O N T A C T L E N S S P E C T R U M S P E C I A L E D I T I O N 2 0 1 7 c l s p e c t r u m . c o m 44 SCLERAL LENSES SCLERAL LENS PROBLEM-SOLVING Problem-solving techniques for scleral lenses for normal corneas are similar to those for larger diameter scleral lenses. Proper care and handling of scleral lenses is critical to success, as dropout rates range from about 25% to 49%, and handling is the primary reason for dropout. 30,31 Various online resources can help with scleral lens application and removal training. Be sure to caution patients that using the plunger on the center of the lens for removal will cause tremendous discomfort. Scleral lenses must clear the cornea completely with- out the presence of bubbles, which can cause discomfort from focal corneal desiccation (Figure 2). Patients typi- cally experience this discomfort 20 to 30 minutes after lens application. If bubbles are present, lenses should be removed and reapplied. Using a more viscous product in the bowl of the lens with application can help elimi- nate the formation of bubbles. If scleral lenses are tight and cause discomfort after 4 to 6 hours of wear, the peripheral curves need to be made flatter and/or toric. Visualizing the lens outside of the slit lamp and/or using anterior segment OCT will aid in viewing conjunctival vessel compression. If residual astig- matism is present, front toric optics can be employed. Fogging in the post-lens fluid reservoir may occur with scleral lens wear. 32,33 This post-lens tear debris may consist of various tear film components, and compli- cations related to tear reservoir clouding are common in eyes with ocular surface disease. 34 With mini-scleral lenses, there tends to be less fogging in the post-lens fluid reservoir compared with larger diameter scleral lenses. PRACTICE MANAGEMENT PEARLS Prescribing scleral lenses for healthy eyes can be an amazing practice-building opportunity that is financially and personally rewarding for patients and practitioners. One report noted that optometrists performed the same number of examinations per hour in 1997 as they did in 2012. 35 This suggests additional opportunities exist for increasing patient volume, productivity, and profitability, specifically related to the average annual contact lens sale per contact lens examination and the average number of months elapsed between eye examinations. 35,36 Particularly concerning is that the average contact lens dropout rate is 16%, even with the availability of premium designs and materials. 8-10,37 This amounts to a sizable number of patients lost over the lifetime of a practice and significant lost revenue. For example, during 45 years of practice, this can have a $2 million impact. 9 Not only is the individual patient lost, there is the "replacement cost" of bringing in a new patient to consider. 36 If you're interested in expanding your scleral lens with traditional contact lenses. 20 While safety eyewear is recommended for all ath- letes, scleral lenses can help protect against trauma. 21,22 TIPS FOR FITTING HEALTHY EYES Essential tools for fitting scleral lenses on healthy eyes include keratometry, topography and/or Scheimpflug imaging, horizontal visible iris diameter, and a scleral lens diagnostic fitting set. Some manufacturers offer em- pirical ordering of scleral lenses for healthy eyes. Inquire about the patient's visual needs, including fre- quency of desired contact lens wear, work requirements, digital device use, hobbies, athletic activities, and gen- eral visual demands. Evaluate the anterior segment for eyelid margin disease, including blepharitis, demodex, aqueous deficiency, and elevations of the conjunctiva, such as pinguecula or pterygium. Stain and evaluate the cornea and conjunctiva with sodium fluorescein prior to scleral lens application. Additional testing, including tear breakup time, Schirmer tear test, tear osmolarity, MMP-9, and mei- bomian gland evaluation, provide useful baseline data, and a dry eye questionnaire can also be helpful prior to scleral lens fitting. Follow the manufacturer's recommendations or the fitting guide to ensure success. After allowing the lens to settle, evaluate the fit with anterior segment optical co- herence tomography (OCT) or sodium fluorescein un- der the lens with a slit beam using white light to deter- mine central and peripheral lens clearance (Figure 1). The general fitting philosophy for normal corneas is to use smaller diameter scleral lenses, also known as mini-scleral lenses. Currently, there are questions about how the combination of lens thickness, material, and post-lens fluid layer affects corneal physiology, hypoxia, and edema. Theoretical modeling studies of oxygen transmissibility and tension agree that scleral lenses should be manufactured with highly oxygen permeable (Dk) materials (>125-150+), low center thickness (200 to 250 microns), and low corneal clearances (less than 150 to 200 microns). 23-27 One study demonstrated that the amount of corneal edema was 1.7% after 8 hours of scleral lens wear. 28 Clinically, the reported edema is not observed and falls below physiological overnight edema, 4% without contact lens wear. 29 Fortunately, for healthy eyes, smaller diameter scleral lenses (14.0 mm to 15.5 mm) are manufactured thinner (250 to 300 microns) and can use minimal clearance. In my experience, scleral lenses do not need excessive clear- ance to vault over the smooth, predictable surface on these corneas. Thus, smaller diameter scleral lenses can be worn successfully without inducing chronic edema on the corneal tissue; however, long-term research is still needed on the effect of scleral lenses on normal corneas.

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