Prismatic rigid gas-permeable (RGP) lenses reduce higher-order aberrations better than nonprismatic RGPs according to a study published in Optometry and Vision Science. The researchers noted a 51% reduction in vertical coma in patients with prismatic RGPs compared with nonprismatic RGPs. The cross sectional analysis consisted of 17 eyes of 17 patients with stage I or II keratoconus (mean age 34.6±11.1 years). Participants were randomized to first be fitted with standard or prismatic RGP lenses, and assessed after 30 minutes for centration, rotation, and movement. Tests measured ocular aberrations, visual performance, and corneal topography. Patients were later fitted with the other lens and assessments were repeated. Prismatic lenses provided lower values for root-mean-square (RMS) higher-order aberrations than the standard RGP contacts (P <.05). Both prismatic and nonprismatic RGPs diminished vertical coma, coma-like, and RMS higher-order aberrations and reduced oblique primary astigmatism and defocus compared with eyes not wearing contacts (P <.05). 

Both study lenses also created a lower degree of positive vertical coma than eyes without contacts. Both RGPs  enhanced low-contrast visual acuity (LCVA) in photopic and mesopic lighting conditions and high-contrast visual acuity (HCVA) at the lower light level. Prismatic RGPs also enhanced HCVA in the photopic condition (P =.01), and standard RGPs raised contrast sensitivity in normal room lighting (P =.03). Visual function improved regardless of whether the RGP contained prism (P ≥.05).

“Different studies using adaptive optics suggested that aberration correction can improve visual performance in patients with keratoconus,” according to the analysis. “However, as several authors concluded, to achieve better image quality, coma and spherical aberration must combine with other aberrations.”


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Investigators performed the wavefront error assessment at 3 mm pupil diameter in a non cycloplegic state. The eye used for data analysis was chosen randomly. The study’s limitations include that it did not explore higher powers of prism and whether an added prism affects oxygen exchange during lens wear. 

Reference

Carballo-Alvarez J, Caballero-Magro E, Cortes-Escudero I, Carpena-Torres C. Correction of ocular aberrations with prismatic rigid gas-permeable contact lenses in keratoconic eyes. Optom Vis Sci. 2021;98(11):1279-1286. doi:10.1097/OPX.0000000000001801