Ahead of The Curve
contact lens management
Ahead of The Curve
Corneal reshaping lens offers traditional four-curve design option.
BRUCE T. WILLIAMS, O.D., F.O.A.A.
As a practitioner who has developed his clinical expertise in corneal reshaping with a traditional four-curve reverse geometry (RG) lens design, I was extremely excited to hear about the recent release of the RG-4, from Paragon Vision Sciences, for two reasons:
1. No single reverse geometry design works for every cornea and sphero-cylindrical treatment target, so it's great to have multiple options.
2. Paragon Vision Sciences already has a proven record of excellence with its Corneal Refractive Therapy (CRT) lens.
Here, I discuss the features of the RG-4 and the ideal candidates for the lens.
The RG-4 is manufactured in HDS (Hyperpurified Delivery System) 100 material, providing patients with high-oxygen permeability. Also, Paragon Vision Sciences has plasma treated the lens to provide surface wettability for further patient comfort.
In addition, the lens contains a laser mark, so you can immediately identify its parameters via slit lamp — a real time saver. Further, the lenses are tinted green (GR) for the right eye and blue (BL) for the left eye to ensure appropriate insertion.
You can fit the RG-4 empirically or with a Paragon diagnostic set. I recommend the fitting set because it saves time and expense, as you can verify the best fit parameters before ordering the final lens. The lens is available in a wide range of parameters with a base curve from 40.00D to 49.00D and diameters from 10.0mm to 12.4mm. I've found that this makes the lens ideal as a primary choice for patients who have low to moderate myopic astigmatism — meaning up to approximately 4.50D of myopia and up to 1.50D of with-the rule astigmatism.
In addition, the RG-4 contains an aspheric alignment zone — a real problem solver for patients who experience difficulties with continuity of treatment due to excessive lens movement or poor lens centration. When adjusting the overall sagittal height for lens centration or fluorescein pattern corrections, the resultant tear layer changes require you to alter the target power to keep the over-refraction with the lens consistent. The resultant final lens is well centered with the appropriate bulls-eye fluorescein pattern exhibiting less than or equal to 0.5mm of movement.
Recently, a 21-year-old white female presented with a refraction of -3.00 -0.50 × 180 OD and -3.50 - 0.25 × 61 OS, correctable to 20/20 O.U. Her initial steep keratometry (k) reading was 45.00D (7.50mm) @ 78, and her flat k reading was 43.87D (7.69mm) @168. By using the RG-4 lens — a design predicated on mean k, which takes advantage of the aspheric alignment zone to accommodate for the rapid flattening in the periphery — the steep k was reduced to 42.50D (7.94mm) @ 70 and the a flat k was reduced to 41.87D (8.06mm) @ 160. The outcome of this fit was a plano refraction O.U. and a very satisfied patient.
As you can see, the RG-4's thoughtful design features, ease of fitting and reliable treatment make it a welcome four-curve reverse geometry design option. OM
DR. WILLIAMS, PRACTICES IN SEATTLE, WASH., SPECIALIZING IN COMPLEX CONTACT LENS FITTING. HE'S A FELLOW OF THE ORTHOKERATOLOGY ACADEMY OF AMERICA (OOA) E-MAIL HIM AT SVISION@QWEST.NET.
MATERIAL: Paragon HDS 100
DK/T: 100 Dk
WEARING SCHEDULE: Extendedwear approval
RECOMMENDED REPLACEMENT SCHEDULE: One year is the typical suggestion
DIAMETER: 10.0mm to 11.2mm
PATIENT COST: $900 to $1600
FITTING SET: 31 lenses
Optometric Management, Issue: October 2008