Which contact lens material is often associated with polymegathism/pleomorphism?

Which contact lens material is often associated with polymegathism/pleomorphism?

• A. Rigid gas permeable
• B. Hydrogels
• C. Silicone hydrogel
• D. PMMA

Answer: (B)

Polymegathism and pleomorphism describe variability in the size and shape of corneal endothelial cells, and they appear on specular microscopy when the endothelium is under stress. A key source of that stress with contact lenses is hypoxia from reduced oxygen reaching the cornea. Hydrogels historically have lower oxygen permeability than silicone-hydrogel materials, so wear over time can create a relatively hypoxic corneal environment. That chronic stress prompts endothelial cells to change size and shape, leading to polymegathism and pleomorphism. In contrast, silicone-hydrogel lenses deliver more oxygen to the cornea, reducing this particular endothelial response, and PMMA—being non-permeable to oxygen—causes other problems rather than this specific pattern. Rigid gas-permeable lenses are also highly oxygen-permeable, so they’re less often associated with this endothelial morphology change.

Polymegathism and pleomorphism describe variability in the size and shape of corneal endothelial cells, and they appear on specular microscopy when the endothelium is under stress. A key source of that stress with contact lenses is hypoxia from reduced oxygen reaching the cornea. Hydrogels historically have lower oxygen permeability than silicone-hydrogel materials, so wear over time can create a relatively hypoxic corneal environment. That chronic stress prompts endothelial cells to change size and shape, leading to polymegathism and pleomorphism. In contrast, silicone-hydrogel lenses deliver more oxygen to the cornea, reducing this particular endothelial response, and PMMA—being non-permeable to oxygen—causes other problems rather than this specific pattern. Rigid gas-permeable lenses are also highly oxygen-permeable, so they’re less often associated with this endothelial morphology change.