CPO FREE CPO Ophthalmic Instrument Maintenance and Calibration Questions and Answers 2

Question 1

When replacing a slit lamp bulb, oil from fingerprints is left on the new bulb. What is the most likely immediate consequence during the next use?

Accepted Answer

Creation of hot spots that reduce the bulb's lifespan.

Answer

Oil from skin creates hot spots on the glass surface of a halogen bulb. These hot spots lead to uneven heating, which stresses the glass and can cause the bulb to fail prematurely, thus reducing its operational life. While a distorted beam could be caused by improper bulb housing placement, the direct effect of the fingerprint oil is the creation of damaging hot spots.

Question 2

A manual phoropter's Jackson Cross Cylinder (JCC) axis knob feels unusually stiff and occasionally slips during rotation. What is the most probable cause that requires professional service?

Accepted Answer

Debris has accumulated around the internal thrust washer mechanism.

Answer

Stiffness and slipping of the JCC axis are classic signs of internal contamination. Debris, often from skin cells, makeup, or environmental dust, can work its way into the cross-cylinder mechanism and build up around the thrust washer and other moving parts. This requires complete disassembly, cleaning, and re-lubrication by a trained technician to resolve.

Question 3

During a Goldmann applanation tonometer calibration check, the feeler arm floats perfectly at the '0' and '2' (20 mmHg) positions but falls toward the examiner at the '6' (60 mmHg) position, even when the dial is at 6.05. This indicates:

Accepted Answer

The tonometer is underestimating high intraocular pressures.

Answer

At the '6' position (representing 60 mmHg), the feeler arm should fall toward the patient when the dial is slightly above 6 (e.g., 6.05) and toward the examiner when slightly below (e.g., 5.95). If it falls toward the examiner even when the dial is set above 6, it means not enough force is being applied by the tonometer's mechanism. This indicates the tonometer is reading lower than the actual pressure, or underestimating, at the high end of its range.

Question 4

An automated lensmeter consistently fails to read high-plus, slab-off bifocal lenses accurately, often giving an 'error' message. Which of the following is the most likely reason for this specific failure?

Accepted Answer

The complex prism and rapid power changes of the slab-off line interfere with the sensor array.

Answer

Automated lensmeters work by analyzing a pattern of light projected through the lens. The sharp, often prismatic power change across a slab-off line, combined with a high-plus power, can distort this light pattern in a way that the instrument's software cannot interpret, leading to a reading error. While other issues can cause general inaccuracies, the specific mention of slab-off bifocals points to this complex optical interference.

Question 5

When performing A-scan biometry, if the gain is set too high, what is the most likely measurement error that will occur?

Accepted Answer

An artificially elongated axial length due to retinal spike broadening.

Answer

Setting the gain too high on an A-scan unit amplifies the return echo. This can cause the retinal spike, which should be sharp, to become broad and thick. The machine may interpret the leading edge of this broadened spike as the retinal surface, leading to a measurement that is longer than the true axial length.

(CPO) Certified Paraoptometric Practice Test

(CPO) Certified Paraoptometric Practice Test

CPO FREE CPO Ophthalmic Instrument Maintenance and Calibration Questions and Answers 2