Vision and Ophthalmology Optics and Refraction 2 — Questions and Answers
Question 1: A patient has +2.00 sphere, -1.00 cylinder, axis 90. What is the power at the 180-degree meridian?
- +1.00 D (Correct answer)
- +2.00 D
- +3.00 D
- -1.00 D
Correct answer: +1.00 D
The cylinder power acts at 180° (perpendicular to axis 90), so the power at 180° is the sphere (+2.00) plus the cylinder (-1.00) = +1.00 D.
Question 2: Which instrument measures the refractive error of the eye by detecting the direction of the reflected light reflex?
- Keratometer
- Lensometer
- Retinoscope (Correct answer)
- Tonometer
Correct answer: Retinoscope
Retinoscopy uses a streak or spot retinoscope to observe the reflex from the patient's fundus, allowing objective determination of refractive error.
Question 3: The principal of 'against motion' in retinoscopy indicates which refractive error?
- Hyperopia
- Myopia greater than the working distance (Correct answer)
- Emmetropia
- Astigmatism along the cylinder axis
Correct answer: Myopia greater than the working distance
Against motion (reflex moves opposite to the retinoscope movement) indicates myopia that exceeds the working distance lens equivalent.
Question 4: The corneal power (in diopters) is primarily due to which interface?
- Air-tear film interface (Correct answer)
- Cornea-aqueous interface
- Iris-lens interface
- Lens-vitreous interface
Correct answer: Air-tear film interface
The air-tear film (air-cornea) interface provides approximately 48 D of the eye's total ~60 D of refractive power due to the large difference in refractive indices.
Question 5: Which refractive condition is present when the eye is too short (axial) or the cornea too flat?
- Myopia
- Hyperopia (Correct answer)
- Astigmatism
- Presbyopia
Correct answer: Hyperopia
Hyperopia occurs when the eye is too short axially or the corneal/lenticular power is too weak, causing parallel rays to focus behind the retina.
Question 6: Vergence refers to which property of a light beam?
- Color wavelength
- Speed of propagation
- Degree of convergence or divergence (Correct answer)
- Polarization state
Correct answer: Degree of convergence or divergence
Vergence measures the degree to which light rays are converging (positive vergence) or diverging (negative vergence) and is measured in diopters.
Vision and Ophthalmology Optics and Refraction 2
A patient has +2.00 sphere, -1.00 cylinder, axis 90.
What is the power at the 180-degree meridian?