ABO Refraction & Visual Acuity — Questions and Answers
Question 1: What does a myopic patient experience without corrective lenses?
- Blurred distance vision (Correct answer)
- Blurred near vision
- Double vision at all distances
- Color blindness
Correct answer: Blurred distance vision
Myopia (nearsightedness) causes light to focus in front of the retina, making distant objects appear blurry while near vision remains clear.
Question 2: Which instrument is used to objectively measure a patient's refractive error?
- Autorefractor (Correct answer)
- Tonometer
- Pachymeter
- Keratometer
Correct answer: Autorefractor
An autorefractor automatically determines the refractive error of the eye by measuring how light changes as it enters the eye.
Question 3: A prescription reads -2.50 -1.00 x 180. What type of correction does this represent?
- Compound myopic astigmatism (Correct answer)
- Simple hyperopic astigmatism
- Mixed astigmatism
- Simple myopia
Correct answer: Compound myopic astigmatism
A negative sphere with a negative cylinder indicates compound myopic astigmatism, where both principal meridians are myopic.
Question 4: What is the Snellen fraction for a patient who can read the 20/40 line?
- The patient sees at 20 feet what a normal eye sees at 40 feet (Correct answer)
- The patient sees at 40 feet what a normal eye sees at 20 feet
- The patient has 40% vision loss
- The patient needs +0.40 D correction
Correct answer: The patient sees at 20 feet what a normal eye sees at 40 feet
In Snellen notation, 20/40 means the patient must be at 20 feet to read what a person with normal vision can read at 40 feet.
Question 5: Which lens power would be prescribed for a patient with +3.00 D of hyperopia?
- Convex (plus) lens of +3.00 D (Correct answer)
- Concave (minus) lens of -3.00 D
- Cylindrical lens of 3.00 D
- Prism lens of 3.00 prism diopters
Correct answer: Convex (plus) lens of +3.00 D
Hyperopia requires a convex (plus) lens to add convergence and move the focal point forward onto the retina.
Question 6: What is the purpose of the Jackson Cross Cylinder during refraction?
- To refine the axis and power of the cylinder correction (Correct answer)
- To measure intraocular pressure
- To evaluate color vision
- To assess pupil dilation
Correct answer: To refine the axis and power of the cylinder correction
The Jackson Cross Cylinder (JCC) is used during subjective refraction to fine-tune both the axis and power of astigmatic correction.
ABO Refraction & Visual Acuity
What does a myopic patient experience without corrective lenses?