RGP insights

Behind the Smile

BY LORETTA B. SZCZOTKA, OD, MS
FEBRUARY 1999

ou may see smile or arcuate patterns if you routinely perform corneal topography when fitting RGPs. These RGP-induced corneal shape changes are most often located in the inferior one-third of the cornea and can implicate a suboptimal fitting   relationship, but not all topography patterns are alike.

Unintentional Corneal Bearing

In traditional RGP fitting, a flattened arcuate compression ring usually signifies unintended corneal molding from the inferior edge of a superiorly decentered contact lens. Just outside of the lens edge, an arcuate zone of steepening appears, best viewed on an instantaneous map (Fig. 1). Secondary clinical signs may include spectacle blur and increased myopia from associated central corneal steepening. These signs may suggest intermittent lens adhesion, and it's necessary to flatten the posterior curves to improve corneal stability.

FIG. 1: Instantaneous map showing arcuate zone of steepening.

Similar patterns frequently appear with back surface aspheric RGP multifocals, which are intentionally fit significantly steeper than K. The anticipated arcuate compression ring is secondary to heavy midperipheral corneal bearing beneath the rapidly flattening aspheric lens periphery.

Other Reasons to Smile

During orthokeratology, undesirable asymmetric corneal molding from a high-riding lens due to a superior corneal apex, lid tension or a flat fit can also result in a smile pattern, explains Scott Schachter, O.D. The patient in Figure 2, courtesy of Dr. Schachter, was wearing a high-riding reverse geometry DreimLens for orthokeratology. The increased superior flattening caused opposite sector inferior steepening, which was intensified with the steeper secondary curve of the reverse geometry lens.

FIG. 2: Patient with (opposite sector) inferior steepening.

FIG. 3: Dr. Mandell's face superimposed on topography map, courtesy of Cynthia Roberts, Ph.D.

Remember too, topography smile patterns can resemble people who have been influential to the development of the field. Robert Mandell O.D., Ph.D., who was recently honored on his 65th birthday at "BobFest: A Corneal and Contact Lens Symposium," is said to be so eminent in corneal topography that some of the happy faces have begun to resemble him (Fig. 3)!

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