CPO CPO Clinical Principles and Procedures — 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.
Question 7: A patient with early-stage glaucoma has a reliable Humphrey Visual Field (HVF) 24-2 test that appears normal. However, the optometrist suspects central defects based on OCT findings. Which of the following ancillary tests would be most appropriate for the paraoptometric to perform to investigate this specific concern?
- A 30-2 visual field test to screen a wider area.
- A 10-2 visual field test to get higher resolution of the central area. (Correct answer)
- Confrontation visual fields to quickly assess peripheral vision.
- An Amsler grid test to check for macular distortion.
Correct answer: A 10-2 visual field test to get higher resolution of the central area.
While a 24-2 test is a standard for glaucoma, it can miss early paracentral defects near fixation. The 10-2 visual field test provides a higher resolution by testing more points (68) within the central 10 degrees, making it more sensitive for detecting subtle defects close to the center of vision that may be indicated by OCT scans but missed on the 24-2 protocol.
Question 8: A long-time progressive lens wearer complains of a persistent 'swimming' sensation and intermittent blur with their new glasses, despite the Rx and measurements being verified as correct. The frame has been adjusted for optimal pantoscopic tilt and face form. What is the most likely underlying cause for this non-adapt issue?
- The vertex distance is too short.
- The progressive lens design is too 'hard' compared to their previous pair. (Correct answer)
- The base curve of the new lenses is too flat.
- The patient has developed a binocular vision disorder.
Correct answer: The progressive lens design is too 'hard' compared to their previous pair.
When standard fitting parameters are correct, persistent 'swim' and peripheral distortion in an experienced wearer often points to an issue with the lens design itself. A 'harder' progressive design has a wider distance and near zone but a more rapidly increasing power corridor, which creates more peripheral aberration. This can induce the swimming sensation for patients accustomed to a 'softer' design with smoother transitions.
Question 9: During a contact lens follow-up, a patient wearing monthly toric lenses complains of fluctuating vision, especially after blinking. Upon slit lamp examination, the paraoptometric notes the toric orientation marking is consistently rotated 15 degrees nasally in the right eye. The over-refraction is +0.25 -0.75 x 100. The current lens is 8.6 BC, 14.5 Diam, -2.00 -1.25 x 085. Applying the LARS rule, what new diagnostic lens axis should be ordered?
- 115 degrees
- 070 degrees (Correct answer)
- 100 degrees
- 055 degrees
Correct answer: 070 degrees
LARS stands for Left Add, Right Subtract. Since the lens is rotated to the paraoptometric's left (nasally in the right eye), you must ADD the 15 degrees of rotation to the original prescribed axis of 085. However, this common application of LARS is from the practitioner's view. A more precise way to think is if the lens rotates nasally (patient's left for the right eye), the correcting axis must be moved temporally. In this case, subtracting from the axis is required for nasal rotation. Thus, 85 degrees - 15 degrees = 70 degrees. This compensates for the consistent rotation to provide stable, clear vision.
Question 10: A 10-year-old is undergoing amblyopia therapy. The prescribed regimen is patching the dominant eye for two hours daily. The parents report inconsistent compliance and ask about alternatives. Which of the following is an equally effective, evidence-based alternative for treating moderate amblyopia in this age group?
- Weekend-only atropine penalization of the dominant eye. (Correct answer)
- Wearing a Bangerter filter full-time over the dominant eye.
- Increasing near-vision therapy activities without patching.
- Switching to an eye patch with a more engaging design.
Correct answer: Weekend-only atropine penalization of the dominant eye.
Large-scale clinical trials, such as those by the Pediatric Eye Disease Investigator Group (PEDIG), have shown that for moderate amblyopia (20/40 to 20/80), weekend atropine use is as effective as 2 hours of daily patching. Atropine drops blur the vision in the dominant eye, forcing the brain to use the amblyopic eye, which can be a more manageable option for families struggling with patch compliance.
Question 11: A paraoptometric is assisting with a low vision evaluation for a patient with advanced macular degeneration. The patient needs to read a newspaper. Which of the following devices would be most appropriate to try first, considering it allows for a wide field of view and keeps the hands free for holding the paper?
- A hand-held monocular telescope.
- A closed-circuit television (CCTV) magnifier.
- High-plus spectacle-mounted microscopes. (Correct answer)
- A hand-held dome magnifier.
Correct answer: High-plus spectacle-mounted microscopes.
For a task like reading a newspaper, which requires a sustained near focus and benefits from having both hands available, high-plus spectacle-mounted microscopes are an excellent starting point. They provide a wide field of view compared to telescopes and free up the patient's hands, unlike hand-held magnifiers. While a CCTV is also hands-free and very powerful, it is less portable and a more complex electronic device to start with for this specific task.
Question 12: During patient triage, a 68-year-old male calls complaining of a 'curtain' coming down over the vision in his right eye that started 30 minutes ago, but he reports no pain or redness. He also mentions a history of high cholesterol. What is the most critical and immediate action the paraoptometric should take?
- Schedule the patient for the next available routine eye exam.
- Advise the patient to monitor the symptom and call back if it worsens.
- Instruct the patient to go to the nearest emergency room immediately.
- Book an urgent, same-day appointment with the optometrist. (Correct answer)
Correct answer: Book an urgent, same-day appointment with the optometrist.
The symptom of a transient, painless, monocular vision loss (amaurosis fugax) described as a 'curtain' is highly suspicious for a retinal vascular occlusion, such as from a Hollenhorst plaque (cholesterol embolus). While it could be a retinal detachment, the transient nature points more towards a vascular event. This is an ocular emergency requiring immediate evaluation by the optometrist to assess for retinal ischemia and determine the need for urgent referral to a specialist or hospital to prevent permanent vision loss or a stroke.
CPO CPO Clinical Principles and Procedures
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?
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