Retina Diagnostic Techniques

Abstract

There are a variety of different methods available to visualize the retina, including
ophthalmoscopy, ocular coherence tomography, and fluorescein angiography. Each
of these methods has its own advantages and disadvantages, and often they are used
in conjunction with one another to provide ophthalmologists with vital information
required for diagnosis, monitoring, and treatment of a variety of ocular conditions.
Below, each of these retinal imaging techniques will be discussed in further detail.

Ophthalmoscopy/Fundoscopy

Ophthalmoscopy (also called ‘fundoscopy’) involves the direct visualization of the
retina by an ophthalmologist using a light source. There are generally two types of
techniques for achieving this: direct ophthalmoscopy (which uses a small handheld
lens with light source [image below]) and indirect ophthalmoscopy (which uses a
head-mounted light and hand-held lens). Though each of these methods has certain
advantages over the other, in most cases either can be used to effectively image the
retina.

Compared to other imaging techniques, ophthalmoscopy is relatively quick and
requires the least high-tech equipment. For this reason, ophthalmoscopy is part of a
routine ophthalmologic exam. However, only a gross anatomical image is provided.
This can often be sufficient to diagnose and monitor much retinal pathology, but
if greater detail is required, one of the other imaging techniques may need to be
employed.

Direct Ophthalmoscope: ophthalmoscopy is relatively quick and requires the least high-tech equipment

Ocular Coherence Tomography

Ocular Coherence Tomography (OCT) is special imaging technique
ophthalmologists can use to visualize the retina. Similar to how an ultrasound uses reflected sound waves to produce an image, OCT uses reflected infrared light to reconstruct the 3-dimensional structure of the retina with exceptional resolution. By being able to visualize the retina in this way, OCT provides ophthalmologists with images they can use to diagnose many conditions, including macular degeneration, glaucoma, and diabetic retinopathy.

The procedure involves directing light in the near-infrared spectrum at the retina,
and measuring the small portion of light that is reflected back from the various
layers of the retina. By doing this, the OCT machine can differentiate between the
different layers of the retina and construct a representative image, with a resolution in the range of micrometers! As OCT is fast (no patient preparation required) and risk-free (no ionizing radiation is involved), it is a technology that has become popular within the ophthalmology community.

Fluorescein Angiography

Fluorescein Angiography is an imaging technique used to visualize the vessels of
the retina. The procedure involves the injection of a special dye, fluorescein, to help
ophthalmologists see the organization of blood vessels within the eye. This can be
useful in monitoring a number of conditions, including diabetes and retinal vein
occlusions.

The procedure itself is relatively simple. First, medications are used to dilate the
pupil and initial images of the retina are taken. Then the patient is given an injection
(generally in to the arm) of fluorescein dye, which will travel through the circulation
to the vessels of the eye. By taking a number of images at various times after
injection, an ophthalmologist is able to visualize the circulation within the eye and
determine if there are any abnormalities. By being able to identify aberrations or
dysfunction of the retinal vessels, ophthalmologists are better able to determine the
most appropriate course of treatment for a number of chronic conditions.

Evan Martow