RGP insights

Tried and Tested Tips For Fitting Pediatric Patients

RGP insights
Tried and Tested Tips For Fitting Pediatric Patients

Many fitters are intimidated by RGPs for pediatric patients. However, fitting RGPs in small children and infants is simpler as the patients are far more adaptable. Following are a few pointers that I have learned over the years.

1 It's OK to estimate pre-fitting measurements, if you can later judge the fit appropriately. Don't get caught up in trying to get the most accurate K measurements or refraction down to the last 0.25D. To begin your fitting, use a hand-held keratometer (if available), but diagnostic trial lenses can also be used as templates to bracket the endpoint. Performing the exam under anesthesia in the hospital setting is your best bet; however, fluorescein evaluations can be done in your exam room if the child cooperates. Add fluorsescein and view the pattern through the cobalt blue filter outside the slit lamp as the child sits on the parent's lap, or use a Burton lamp or a blue filter atop a penlight. Don't forget to measure corneal diameter using calipers or a mm ruler, because the lens diameter will depend on this.

Figure 1. This young patient assists by holding up her own trial lens, with the help of Laa Laa.

2 Select the overall diameter (OAD) 1mm to 2mm smaller than corneal diameter. These lenses are fit larger than adult OADs to prevent loss and optical zone decentration. Many pediatric RGPs are high-powered plus lenses that have small lenticular caps and may induce distortion when viewing eccentrically through the OZ.

3 Always use high or hyper Dk materials which allow you to create custom parameters without worrying about hypoxia. Remember that even though no oxygen stress may be noted in the short term with low Dk lenses, these patients will likely be wearing lenses for a lifetime, and the cumulative effect of low Dk may not be detected until years later. My favorite materials are Fluoroperm 92 or 151, Boston XO or Menicon Z.

4 Fit steeper to prevent loss. I routinely fit to achieve apical clearance which averages 1.00D steeper than flat K.

5 Fine tune based on trial lens powers and the over-refraction (or over-retinoscopy for infants). You can also design lenses empirically from the spectacle refraction, but remember to correct for vertex distance which can create surprisingly large jumps in high prescriptions. A +20.00D spectacle lens converts to a +26.30D contact lens. Also, it is not uncommon for a positive tear layer of about 2.00D to form if the lenses are fit steeper.

6 In the first year, aphakic lens powers range from +20.00D to +40.00D, and the average lens Rx is +31.00D. In the first month of life, 80 percent of infants require Rx changes due to growth, and a ­5.00D change occurs by 24 months. All infants must be overcorrected at near by +3.00D until age 2, by +1.00D to +1.50D between 2 to 3, and then move the child to a distance contact lens with bifocal spectacles after age 3.

7 Include young patients in fitting and follow-up. Make them feel like little helpers. They will soon be serving as their own assistants by holding up trial lenses as you perform the over-refractions (Figure 1).

Dr. Szczotka is an Associate Professor at Case Western Reserve University Dept. of Ophthalmology and Director of the Contact Lens Service at University Hospitals of Cleveland.