Glossary

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TermDefinition 
 
PolymegathismAn irregular variation of endothelial cell sizes.View
Polymethyl methacrylate See also PMMA. View
PresbyopiaA condition in which the crystalline lens loses flexibility, resulting in an inability to focus on near objects.View
PreservativeA naturally occurring or synthetically created substance that is added to a product to prevent bacterial contamination or other undesirable chemical changes. View
Prism BallastA stabilization technique where prism is added to weight the bottom edge of a contact lens.View
PRKReshaping the anterior central cornea using an excimer laser to ablate tissue from the stromal layer of the cornea. In PRK, the epithelium is removed prior to ablation. View
Progressive Multifocal Contact LensesSee also Simultaneous Multifocal Contact Lenses.View
Punctate StainingA corneal fluorescein pattern where pinpoint epithelial defects are noted.View
Radial Edge LiftSee also Edge Lift. View
Radial KeratotomyA type of refractive surgery that reduces myopia by flattening the cornea with small radial incisions.View
RadiuscopeAn instrument used for measuring the radius of curvature of the surfaces of a contact lens by means of the Drysdale method.View
Refractive ErrorBlurred vision caused by an inability of light rays to focus on the retina.View
Refractive SurgeryAn alteration of the corneal surface by laser, implants or incisions with the purpose of correcting refractive error.View
Residual Astigmatism Remaining astigmatism after the correction of a refractive error. See also Astigmatism.View
Retainer LensRigid lens worn at night for Orthokeratology. See also Orthokeratology. View
Reverse Geometry LensA lens which the central optical zone has a flatter radius of curvature than the adjacent curvatures.View
Reverse Piggy Back LensA fitting technique that uses a combination of soft contact lenses above a rigid gas permeable contact lens.View
RGPRigid Gas Permeable contact lensView
Rose BengalA dye which stains dead or degenerated epithelial cells. View
Sagittal depthThe distance in height between the apex of an arc and the base it rests upon.View