The retina is a thin layer of light-sensitive tissue in the back of the eye. It receives the light rays focused by the lens and converts them to visual signals that are interpreted by the brain. Your retina plays a crucial role in making sure you have clear vision, and your optometrist will examine it when evaluating your eye health.
OCT retinal layer scanning is one of the tests opticians use to evaluate the retina, and it is highly effective in detecting eye conditions and abnormalities.
Why is retinal health important?
A healthy retina is important for eyesight. When the retina is damaged, it can lead to impairment or loss of vision. Many eye conditions involve the retina, most commonly macular degeneration, diabetic retinopathy and central serous retinopathy. Often, the most successful treatment or management of these conditions relies on early detection, which is why it's so important to have your retinal health checked every year or two years.
What are the 10 layers of the retina?
The retina is an approximately 0.4 mm thick membrane that lines the inside of the eye. It functions like a camera: the lens and cornea focus an image onto the retina, this image is then converted to electrical signals which are carried to the brain through our nerve fibres. Once these signals reach the brain, we interpret them as visual images.
There are 10 distinct layers of the retina:
- Internal limiting membrane
- Inner retinal nerve fibre layer
- Ganglion cell layer
- Inner plexiform layer
- Inner nuclear layer
- Outer plexiform layer
- Outer nuclear layer
- External limiting membrane
- Photoreceptor (rod and cone) layer
- Retinal pigmented epithelium
What are the benefits of an OCT scan?
An OCT scan performs a complete mapping of the eye. This helps optometrists to spot the early signs of eye diseases, before you notice a change in your vision.
In addition to the retina in the back of the eye, the optic nerve and retinal nerve fibre layer may be assessed to detect early signs of glaucoma.
An important advantage of OCT scanning is that it can detect each layer of the retina separately. The high-resolution, cross-sectional 3D images obtained by OCT scanning can sometimes reveal otherwise undetectable changes in the retina in people who have no other signs and symptoms.1
Why is it important to scan each retinal layer?
Being able to identify and distinguish the different layers of the retina allows opticians to pinpoint any abnormalities to a specific layer, which provides clues about the possible cause.2 This can help differentiate between two conditions that have very similar clinical signs and symptoms but require different treatment, such as for dry and wet macular degeneration.
For example, when using an ophthalmoscope or fundus photo, drusen and exudates (which are different types of deposits under the retina) often look similar.2 An OCT eye scan can easily distinguish between the two based on their location in the retinal layers. Knowing where these deposits are help to determine what's causing them, and can give your optometrist a more accurate picture of what is happening in your eye.
What is the retinal nerve fibre and what does retinal nerve fibre thinning mean?
The retinal nerve fibre layer (RNFL) in the retina contains ganglion cells, which are a type of neuron or nerve cell that work by transmitting nerve impulses.
Thinning of the nerve fibre layer in the retina is thought to be associated with reduced cognitive performance, i.e. mental abilities such as learning, thinking, reasoning, decision making, and problem-solving. It has also been linked to glaucoma in some cases.
Other conditions OCT can help detect through retinal nerve fibre thinning
There are many possible causes of retinal thinning that can be detected through OCT scanning. The most common are signs of retinal atrophy (scars) caused by age-related macular degeneration, the thinning of the middle ganglion cell layer due to glaucoma, or the thinning due to systemic conditions such as fibromyalgia or multiple sclerosis (chronic stage). 3, 4, 5
Researchers have also found that optical coherence tomography angiography (OCT-A), a variation of the OCT eye scan, can detect microscopic changes in retinal blood vessels that indicate progression towards Alzheimer’s disease.6 This could mean that non-invasive OCT retinal layer scanning may be a valuable tool in the future for detecting the early signs of conditions like Alzheimer’s before symptoms appear.7
1. Faghihi H, Hajizadeh F, Riazi-Esfahani M. Optical coherence tomographic findings in highly myopic eyes. J Ophthalmic Vis Res. 2010;5(2):110–121. [Online]. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3380683/ [Accessed 21 November 2019].
2. Heidelberg Engineering. (no date). Know Your Retinal Layers. [Online]. Available at: https://www.heidelbergengineering.com/int/news/know-your-retinal-layers-33401465/ [Accessed 21 November 2019].
3. Brandl C, Brücklmayer C, Günther F, et al. Retinal Layer Thicknesses in Early Age-Related Macular Degeneration: Results From the German AugUR Study. Invest Ophthalmol Vis Sci. 2019;60(5):1581–1594.
4. Morooka S, Hangai M, Nukada M, et al. Wide 3-dimensional macular ganglion cell complex imaging with spectral-domain optical coherence tomography in glaucoma. Invest Ophthalmol Vis Sci. 2012;53(8):4805–4812.
5. Petzold A, Balcer LJ, Calabresi PA, et al. Retinal layer segmentation in multiple sclerosis: a systematic review and meta-analysis. Lancet Neurol. 2017;16(10):797–812.
6. Cunha LP, Almeida AL, Costa-Cunha LV, Costa CF, Monteiro ML. (2016) The role of optical coherence tomography in Alzheimer’s disease. International Journal of Retina and Vitreous 2(24): eCollection. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5088456/ [Accessed 21 January 2020].
7. Doustar J, Torbati T, Black KL, Koronyo Y, Koronyo-Hamaoui. (2017) Optical coherence tomography in Alzheimer’s Disease and other neurodegenerative diseases. Frontiers in Neurology 8: 701. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5742098/ [Accessed 21 January 2020].