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's spectacle Rx is -4.00 -2.00 x 180. Using the spherical equivalent, what power soft contact lens would you initially trial?
Answer: -5.00 D
Spherical equivalent = sphere + (cylinder/2) = -4.00 + (-2.00/2) = -4.00 + (-1.00) = -5.00 D.
Which contact lens material property is described by the term 'wettability'?
Answer: The degree to which the lens surface attracts and retains the tear film
Wettability refers to how well the tear film spreads and adheres to the lens surface; poor wettability leads to dry spots, discomfort, and visual fluctuation.
During slit-lamp evaluation of a newly fitted soft contact lens, what finding indicates the lens may be too tight?
Answer: Conjunctival blanching at the lens edge
Conjunctival blanching (vessel compression) at the lens edge indicates excessive tightness causing mechanical restriction of blood flow at the limbus.
What is the recommended minimum central corneal clearance (vault) when fitting a scleral contact lens?
Answer: 200–400 microns
A minimum central clearance of approximately 200 microns (some guidelines say 200–400 µm) is recommended at dispensing to account for settling over the wear period.
A rigid contact lens has a Dk of 100 and a center thickness of 0.20 mm. What is its Dk/t value?
Answer: 500
Dk/t = Dk ÷ thickness in cm = 100 ÷ 0.020 cm = 500 × 10⁻⁹ (Fatt units); dividing 100 by 0.02 gives 500.
Which condition is characterized by fine, diffuse corneal punctate staining in a patient wearing silicone hydrogel lenses with a preserved multipurpose solution?
Answer: Solution-induced corneal staining (SICS)
Solution-induced corneal staining (SICS) results from an incompatibility reaction between certain preservatives (especially PHMB or Alexidine) and silicone hydrogel lens materials.
When converting a spectacle prescription with vertex distance 12 mm to a contact lens power for a highly myopic patient (-10.00 D spectacles), the contact lens power will be:
Answer: Less minus than the spectacle Rx
Moving a minus lens closer to the eye (from 12 mm vertex to contact lens position) reduces its effective power; thus, the contact lens needs less minus than the spectacle prescription.