CPO CPO Clinical Principles and Procedures 2 — Questions and Answers
Question 1: A patient with keratoconus is scheduled for a topography measurement. During the procedure, the technician notices the mires are significantly distorted and cannot be aligned properly. What is the most appropriate immediate action?
- Record the readings as 'unobtainable' and inform the doctor.
- Reposition the patient's head and reinstruct them on fixation, then attempt the measurement again. (Correct answer)
- Switch to a manual keratometer to get an approximate reading.
- Instill a lubricating eye drop and wait five minutes before reattempting the measurement.
Correct answer: Reposition the patient's head and reinstruct them on fixation, then attempt the measurement again.
In cases of severe corneal irregularity like advanced keratoconus, mire distortion is common. Before concluding the test is unobtainable, the first step is to ensure proper patient alignment and fixation, as this is the most frequent cause of measurement error. Re-positioning and re-instructing the patient may resolve the issue and allow for a usable reading. Lubricating drops might help with surface irregularities but re-positioning is the primary troubleshooting step.
Question 2: When performing indentation gonioscopy with a 4-mirror lens, pressing gently on the cornea can help differentiate between appositional and synechial angle closure. If the angle opens upon indentation, what does this signify?
- The presence of a plateau iris configuration.
- Permanent peripheral anterior synechiae (PAS).
- Appositional angle closure due to pupillary block. (Correct answer)
- Pigment dispersion syndrome.
Correct answer: Appositional angle closure due to pupillary block.
Indentation gonioscopy temporarily increases the aqueous pressure in the anterior chamber, pushing the peripheral iris posteriorly. If the angle is closed simply by the iris being pushed against the trabecular meshwork (appositional closure), this maneuver will physically open the angle. If the angle remains closed despite indentation, it indicates the iris is physically stuck to the meshwork by adhesions (synechial closure).
Question 3: A 68-year-old patient reports a sudden, painless 'curtain' or 'shadow' in their inferior visual field that started one hour ago. Visual acuity is 20/200 in the affected eye. Which of the following pre-testing procedures is most critical to perform urgently before the patient sees the optometrist?
- Stereo acuity testing to assess binocularity.
- Color vision testing with Ishihara plates.
- Confrontation visual fields. (Correct answer)
- Automated refraction.
Correct answer: Confrontation visual fields.
The patient's symptoms are highly suggestive of a retinal detachment, which is an ocular emergency. A superior retinal detachment would cause an inferior visual field defect. Confrontation visual fields can quickly and effectively map out the extent of the suspected field loss, providing critical information for the doctor to confirm the diagnosis. The other tests are less relevant to the immediate, urgent nature of the chief complaint.
Question 4: During pachymetry measurement prior to refractive surgery, a reading of 495 microns is obtained. How does this finding potentially impact the patient's candidacy for the procedure?
- It is a normal corneal thickness and has no impact on candidacy.
- It indicates the cornea is thicker than average, making the patient an ideal candidate.
- It suggests the presence of corneal edema, requiring further investigation.
- It indicates a thinner-than-average cornea, which may limit the amount of tissue that can be ablated. (Correct answer)
Correct answer: It indicates a thinner-than-average cornea, which may limit the amount of tissue that can be ablated.
Average central corneal thickness is approximately 540-550 microns. A reading of 495 microns is considered thin. In laser refractive surgery (like LASIK), a portion of the corneal tissue is removed. A thinner cornea means there is less tissue to work with, which can be a limiting factor, especially for higher prescriptions, and may increase the risk of postoperative complications like ectasia.
Question 5: Which of the following is an essential step when preparing a patient for fundus photography, but is NOT typically required for standard automated perimetry?
- Obtaining informed consent for the procedure.
- Patching one eye to improve fixation.
- Instilling mydriatic drops to dilate the pupil. (Correct answer)
- Explaining the importance of not blinking during the test.
Correct answer: Instilling mydriatic drops to dilate the pupil.
Fundus photography requires a clear, wide view of the retina. To achieve this, mydriatic (dilating) drops are almost always used to enlarge the pupil, allowing the camera to capture a larger area of the fundus without interference from the iris. While some newer systems offer non-mydriatic options, dilation is standard for a comprehensive view. Automated perimetry (visual field testing) is performed with the patient's natural pupil size.
Question 6: A patient with a history of recurrent corneal erosions is being evaluated. The optometrist orders a test to assess the health and density of the corneal endothelial cells. Which instrument would the paraoptometric be expected to use for this procedure?
- Optical Coherence Tomographer (OCT)
- Pachymeter
- Corneal Topographer
- Specular Microscope (Correct answer)
Correct answer: Specular Microscope
A specular microscope is specifically designed to visualize and analyze the corneal endothelium, which is the innermost layer of the cornea. It provides high-magnification images that allow for the assessment of cell size, shape (pleomorphism), and density (cell count), which are critical indicators of corneal health.
CPO CPO Clinical Principles and Procedures 2
A patient with keratoconus is scheduled for a topography measurement.
During the procedure, the technician notices the mires are significantly distorted and cannot be aligned properly.
What is the most appropriate immediate action?