Advertisement

PentaVision

Contact Lens Spectrum

Article

HYBRID HOW-TO

THE BLUES TELL A STORY IN HYBRID LENS FITTING

By: STEPHANIE RAMDASS, OD, MS, MBA
Contact Lens Spectrum October 1, 2020 Vol 35, Issue October 2020 Page(s): 21

In-office use of sodium fluorescein (NaFl) with hybrid lenses has historically been restricted to high-molecular-weight formulations to avoid discoloration of the HEMA soft lens component of older designs. By applying normal NaFl on the ocular or contact lens surface and by using a cobalt blue filter, many clinical observations can be made regarding the fit of today’s hybrid lenses.

Sodium Fluorescein Use

During Fitting If a diagnostic lens set is used for a hybrid lens fit, it is likely to assess the vault of the hybrid lens over an irregular corneal surface, similar to a scleral lens fit assessment. NaFl instilled into the bowl of a trial hybrid lens filled with preservative-free saline is applied on eye and evaluated within the first few minutes. The tear chamber above the corneal apex of a vault-based hybrid lens should be about half the thickness of the GP portion of the lens (Figure 1). Fluorescein can also be placed on the surface of the lens to accentuate the thickness of the GP center for evaluation purposes.

Figure 1. NaFl is placed inside the bowl of a hybrid lens and on the lens surface to easily visualize the GP lens thickness in relation to lens vault over the cornea.
Figure 1. NaFl is placed inside the bowl of a hybrid lens and on the lens surface to easily visualize the GP lens thickness in relation to lens vault over the cornea.

During Initial Dispense Empirically fit hybrid lenses for regular corneas, in which the GP center masks any underlying corneal astigmatism, are typically observed without the aid of NaFl. Predicted base curve calculations, in conjunction with an expected dioptric range for over-refraction, are markers for adequacy of fit. If NaFl is applied to the front surface of a hybrid lens that is fit on a regular spherical or astigmatic cornea, expect to see NaFl creep under the lens surface within the first minute of wear to highlight adequate tear exchange upon blink and a mobile lens. With fluorescein diluted in the layer of tears between the back of the lens and the front of the cornea, you will see a thin characteristic layer of NaFl under the GP center and a more intense NaFl ring at the GP/soft skirt junction corresponding to the clearance of the hybrid lens over the cornea (Figure 2).

Figure 2. In an ideal hybrid lens fit, pockets of clearance between the back of a lens and the cornea (i.e., at the junction), in addition to lens movement with each blink, allow NaFl to seep under the lens and dilute the tear layer present.
Figure 2. In an ideal hybrid lens fit, pockets of clearance between the back of a lens and the cornea (i.e., at the junction), in addition to lens movement with each blink, allow NaFl to seep under the lens and dilute the tear layer present.

During Follow up At follow-up visits, when evaluating the integrity of the cornea and conjunctiva, look for signs of a tight lens fit and seal off of the soft skirt and/or GP portion of the lens on eye (Figure 3). When tears become stagnant beneath the adhered hybrid lens, hyper-fluorescence of particles on the surface of the cornea can be observed; this confirms that a change in the skirt curve or base curve is warranted to loosen the lens fit and to promote adequate tear exchange. CLS

Figure 3. When a hybrid lens skirt is fit too steep, the lens can seal off on the surface of the eye, and tear exchange ceases. This can leave characteristic ring patterns on the surface of the cornea that show where the hybrid lens was sitting.
Figure 3. When a hybrid lens skirt is fit too steep, the lens can seal off on the surface of the eye, and tear exchange ceases. This can leave characteristic ring patterns on the surface of the cornea that show where the hybrid lens was sitting.

Dr. Ramdass is in private practice in Toronto, Canada. You can reach her at StephanieRamdass@ferris.edu. She has received travel funding from Paragon Vision Sciences and lecture honoraria from Wink Productions, Inc. and Bausch + Lomb.

What to Read Next