Contact Lenses Flashcards
7 cards from real ABO 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 Lenses flashcards as text
A patient wearing soft contact lenses complains of reduced vision late in the day. Slit-lamp examination reveals corneal neovascularization at the superior limbus. What is the most likely cause?
Answer: Chronic hypoxia from low-Dk lens
Chronic hypoxia from wearing low-oxygen-transmissible (low-Dk) lenses causes limbal vessel ingrowth to compensate for oxygen deprivation.
Which base curve selection guideline applies when fitting rigid gas-permeable (RGP) contact lenses?
Answer: Align the lens base curve with the flattest K
The standard RGP fitting philosophy is to align the lens base curve with the flattest keratometry reading to achieve an 'on K' or alignment fit.
A toric soft lens rotates 15° nasally on a patient's left eye. Using the LARS rule, how should the lens axis be adjusted?
Answer: Add 15° to the prescribed axis
LARS (Left Add, Right Subtract) means if the lens rotates left (nasally on left eye), add that amount of degrees to the prescribed axis.
What is the primary advantage of silicone hydrogel contact lenses over conventional hydrogel lenses?
Answer: Significantly higher oxygen transmissibility (Dk/t)
Silicone hydrogel lenses have dramatically higher Dk/t values due to silicone's high oxygen permeability, reducing hypoxia-related complications.
A patient presents with acute red eye after sleeping in extended-wear contact lenses. Slit-lamp shows a stromal infiltrate with an overlying epithelial defect and mucopurulent discharge. What condition is most suspected?
Answer: Microbial keratitis
An epithelial defect with stromal infiltrate and mucopurulent discharge is the hallmark presentation of microbial keratitis, a vision-threatening emergency.
Which contact lens parameter describes the amount of lens material per unit area of lens surface?
Answer: Dk/t (oxygen transmissibility)
Dk/t (oxygen transmissibility) accounts for the lens Dk divided by its thickness (t), reflecting actual oxygen passage through the specific lens as worn.
A bitoric RGP lens is indicated when the difference between corneal toricity and residual astigmatism exceeds what threshold?
Answer: 1.00 D
When residual astigmatism (internal astigmatism not corrected by the lens-tear interface) exceeds approximately 1.00 D, a bitoric lens design is indicated.