The aim of this series is to use high quality video to take the registrant through the process of data capture using an OCT. A feed taken directly from an instrument has been processed and annotated/edited to show, in the first exercise, the process of setting up the patient, selecting a programme, and capturing the very first data.
The aim is to help those eye care practitioners, both optometrists and dispensing opticians, to think about the various factors that need to be borne in mind when undertaking an OCT assessment. The video is supported by references and a practical guide accessible if required to help the viewer.
Having viewed the video above, please attempt the following questions. Some of them are based around information revealed in the video, some require some further reading. A list of further reading and useful sources of information relevant to this exercise is found below.
Model answers
Correct answers are in bold italic
1 Which of the following statements regarding sterilisation of chinrests is true?
A Cleansing at the start of a busy clinic and again at the end of the clinic is appropriate
B Professional bodies publish guidelines stating that chinrests should be cleansed with an appropriate surface cleaner between each patient
C Cleaning a chinrest too often risks causing adverse contact response on patient’s chins
D Most proprietary chinrests are of a material that cannot be cleaned with standard disinfection agents
2 Which of the following scans types are most appropriate for initial macular assessment?
A Volume scan
B Annular scan
C Line scan through fovea
D Volume scan and line scan
3 On a colour coded thickness map, which colour is most likely to signify an area of oedema?
A Green
B Blue
C Red
D Yellow
4 Which of the following statements regarding patient blinking during a scan is true?
A Blinking should be avoided during a scan to avoid interruption of the signal
B Blinking should be undertaken prior to the scan rapidly and then avoided during the scan
C Blinking regularly helps maintain a steady signal by replenishing the tear film
D Blinking makes no difference at all to the quality of a retinal scan
5 In order to establish a ‘twin peaks’ plot of the retinal nerve fibre layer thickness, fixation is maintained to allow the measurement point to be centred where?
A Fovea
B Paracentral area
C Peripapillary area
D Centre of the disc
6 What can a high density macular scan reveal about a glaucoma patient?
A Retinal nerve fibre bundle defect
B Ganglion cell complex thickening
C Arcuate scotoma
D Nothing, as the macula is unrelated to glaucomatous damage
Further reading
Clinic Hygiene Principles
- Both the College of optometrists and ABDO have reasonably comprehensive rules regarding sterilisation of surfaces and of anything in close proximity to patients that might threaten contamination. Remember it is these guidelines that might be used as a benchmark of reasonable action and against which your actions might be compared were there to be any investigation or complaint against your procedures. It is, therefore, always worth knowing your professional body’s guidelines.
- http://www.college-optometrists.org/en/utilities/document-summary.cfm/docid/EBEDBDAB-AD05-404C-8850B2E9D5A2EE37
- http://guidance.college-optometrists.org/guidance-contents/safety-and-quality-
- http://www.abdo.org.uk/advice-guidelines/
Basics of OCT
- Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science. 1991, 254;1178-1181.
This paper is perhaps most noteworthy as a historical milestone. The images represented were necessarily grainy as a time domain system was the first in use to analyse differences in reflected radiation from either tissues or a reference mirror. This limits the resolution and it was a few more years before Fourian analysis theory helped the introduction of spectral domain analysis, allowing the much better resolution images we are now used to (look at the scan through the fovea in the video).
For a good all round and comprehensively referenced guide to OCT and all its applications, my recommendation would be;
- Schulman J S et al (editors). Optical coherence tomography of ocular diseases. Slack Publications
Now in its third edition, this book is well illustrated and the technical level is not too daunting.
- At the start of 2013, Optician ran a series of ‘walkthrough’ guides to OCT use and image analysis which are case centred so work well for the clinicians wanting to see more on this subject matter.