2020–2021 BCSC Basic and Clinical Science Course™
3 Clinical Optics
Chapter 5: Contact Lenses
Chapter Exercises
Questions
-
5.1. A 40-year-old patient is prescribed single-vision glasses −6.00 D OU and also fitted with contact lenses −5.50 D OU. He calls to complain that he has trouble reading when wearing the contacts. What is the most likely explanation?
-
The contact lenses are “over-minused.”
-
With the contacts, he is losing near effectivity, which the glasses give him.
-
Looking through the contacts causes base-in prism, making it difficult for the eyes to converge.
-
The contacts have plus-powered tear lenses, which increase accommodative demand.
-
5.2. A patient tore her soft contact lens, and it has caused a corneal abrasion. What is the next step?
-
Put in a fresh lens, which will have a bandage effect, while the abrasion heals.
-
Put in a fresh lens and use topical antibiotics for several days.
-
Pressure-patch the eye with antibiotic and see the patient the next day.
-
Do not use a contact lens; use lubrication and perhaps antibiotic drops.
-
5.3. A trial soft contact lens moves excessively with eyelid blinks. Which of the following would decrease lens movement?
-
flattening the base curve while maintaining the diameter
-
decreasing the diameter while maintaining the base curve
-
increasing the power of the contact lens
-
steepening the base curve while maintaining the diameter
-
flattening the base curve and decreasing the diameter
-
5.4. You fit a patient who has −3.50 D of myopia with an RGP contact lens that is flatter than K. If the patient’s average K reading is 7.80 mm and you fit a lens with a base curve of 8.00 mm, what is the shape of the tear lens?
-
plano
-
teardrop
-
concave
-
convex
-
5.5. For the patient in question 5.4, what power RGP lens should you order?
-
−3.50 D
-
−4.00 D
-
−2.00 D
-
−2.50 D
-
5.6. You fit a toric soft contact lens on a patient with a refractive error of −2.50 D −1.50 × 175. The trial lens centers well, but the lens mark at the 6-o’clock position appears to rest at the 5-o’clock position when the lens is placed on the patient’s eye. What power contact lens should you order?
-
−2.50 D −1.50 × 175
-
−2.50 D −1.50 × 145
-
−2.50 D −1.50 × 55
-
−2.50 D −1.00 × 175
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.