Contact Lens Principles Flashcards
7 cards from real COT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Contact Lens Principles flashcards as text
Which condition describes superficial punctate staining in a 3 o'clock and 9 o'clock distribution on the cornea during RGP lens wear?
Answer: Desiccation staining from incomplete blinking
Peripheral desiccation staining at 3 and 9 o'clock positions occurs when the area adjacent to the rigid lens is not adequately covered by the tear film during blinking.
A scleral contact lens differs from a corneal RGP lens primarily because it:
Answer: Vaults entirely over the cornea and rests on the sclera
Scleral lenses have a large diameter (15–25 mm) that vaults over the entire cornea and lands on the scleral conjunctiva, creating a fluid reservoir.
What is orthokeratology (ortho-k)?
Answer: Use of specially designed rigid lenses worn overnight to temporarily flatten the cornea
Orthokeratology uses reverse-geometry rigid lenses worn during sleep to temporarily reshape the corneal epithelium, providing clear unaided daytime vision.
Which measurement tool is used to evaluate contact lens fit parameters such as base curve, diameter, and thickness?
Answer: Radiuscope (ophthalmometer)
A radiuscope (also called an optical spherometer) measures the back surface radius of curvature of rigid contact lenses.
Microcystic corneal edema seen at the slit lamp is an early sign of which contact lens problem?
Answer: Chronic corneal hypoxia from insufficient oxygen transmissibility
Microcystic edema (epithelial microcysts) develops when chronic hypoxia disrupts normal epithelial cell metabolism and turnover.
Which lens design is most appropriate for a presbyopic patient requiring good distance and near correction in the same eye simultaneously?
Answer: Simultaneous-vision multifocal contact lens
Simultaneous-vision multifocal lenses present distance and near zones to the pupil at the same time, allowing the brain to select the appropriate focus.
What is the clinical significance of the 'sagittal depth' (sag) of a contact lens?
Answer: It describes how deep the bowl of the lens is relative to the fitting surface
Sagittal depth determines how the lens vaults over the cornea; it is influenced by both the base curve and the overall lens diameter.