At this point, most ophthalmic technical staff are at least familiar with optical coherence tomography (OCT) in practice. OCT offers a plethora of data for the clinician, whether it be anterior segment OCT for evaluating corneal layers, angles, anterior chamber (AC) depth, iridotomy or placement of IOL, or posterior OCT to image retinal and choroidal layers, as well as ganglion cell and nerve fiber layer thickness in glaucoma. All analysis data is based on the acquisition of the images — and that is the responsibility of the technician/imager.

Acquiring scans correctly to allow for accurate analysis is a huge responsibility, and it requires a few fundamental, but very important skills. Read on for my review of those skills.

Skill No. 1: Understand how the system works

This is a necessity when utilizing any diagnostic device. OCT emits an infrared wavelength of light that passes through anatomical layers, and the backscattering and reflective light returns; the interference of light is measured, and the density of each layer is demonstrated. This produces a cross section of the anatomy being imaged.

Imagers often do not utilize OCT to its full potential. An example is the enhanced depth-imaging (EDI) function, which can be applied to obtain better detailed structures in the deeper retinal layers and choroid. A prime example of this is using EDI to illustrate thickened choroid in central serous chorioretinopathy (Figure 1).

Skill No. 2:
Recognize artifacts and know how to remedy them

Artifacts are defined as unintentional defects on an image that may interfere with the true image. OCT utilizes light to produce an image, therefore anything that affects light will affect the image. Dry eye, cataract and vitreous opacities are examples of light-interfering pathology. Blinking during acquisition should be encouraged, and use of artificial tears may help. If artifacts are not recognized and fixed, they may be passed on as true pathology or render the image unusable (Figure 2).

Skill No. 3:
Understand what normal looks like

Once an imager understands what a normal OCT looks like, they have the foundation to master the remainder of the skill set. Understanding normal anatomy requires knowing each layer of the structure and normal thickness representation on analysis as well as recognizing normal variants of these structures.

Skill No. 4:
Recognize ocular anatomy

This may seem simple, but placement of the scan is typically not automatic or computer driven (although it can be in some systems). Spectral domain OCT (one of the most common devices) uses a scan that is typically 2 microns in width, and it may be up to the imager to determine where the scan is placed on the anatomy. If scans are misplaced, pathology may be missed, leading to misdiagnosis.

An example of this is acquiring retinal nerve fiber layer (RNFL) thickness scans for glaucoma evaluation. This scan is not linear but is circular and centered over the optic nerve head. Understanding that the nerve fiber is the layer being evaluated, the imager knows the level of the retinal structures to focus on.

Frequently, untrained imagers will focus on larger structures that are easier to see on the corresponding infrared fundus image. In this case, imagers may focus on the deeper laminae cribrosa, not the nerve fiber layer. While nerve fiber layer is transparent, focusing on retinal blood vessels at the optic nerve head will result in a more accurate scan. In Figure 3, the resulting analysis is altered solely based on the level of focus.

Skill No. 5:
Understand disease and how pathology presents on OCT

An understanding of how common pathology appears on OCT enables the imager to “dig deeper” and produce images that clearly define the pathology in question. A classic example is OCT for lamellar macular holes. In some cases, initial scans may not illustrate the excavation of the fovea, as the patient is subjectively fixating on an internal (or external) light (Figure 4). Our brains are trained to find the area of best acuity, and that may fall outside the damaged fovea in these patients.

If the center of fixation is scanned, the images may not reveal the pathology. This scenario emphasizes the importance of a few of the skills necessary to image properly: recognizing ocular anatomy, understanding how disease affects a patient’s vision, and understanding how pathology presents on OCT.

Conclusion

Not all OCT scans are created equal, so don’t regard OCT acquisition as just a matter of “point and shoot.” Along with the fundamental technical skills needed, as outlined above, the imager needs to know the specific area of the eye, suspected disease, and results required. When scanning patients, the imager must think about the structures of the anatomy being scanned, paying particular attention to the resulting scans, and adapting them to produce the most information for the clinician to make a diagnosis. OP