Optical Coherence Tomography (OCT)

Optical coherence tomography (OCT) tells us more about the health of your eyes than we could ever learn just by looking. OCT is a non-contact, non-invasive technique that scans the structure of your eye and creates a 3-D image of every detail, including aspects that cannot be investigated by other methods. Our spectral-domain OCTs are the ultimate tools for diagnosis and monitoring of your macula and optic nerve, allowing early detection of glaucoma, macular degeneration and many other retinal conditions. In most cases it is able to detect structural damage before patients notice problems themselves so that subsequent treatment may arrest any loss of vision.

OCT is also a fantastic way to monitor corneal pathology and the fitting of soft and rigid contact lenses, from the most simple to the most complicated.

As of September 2017, Innovative Eye Care in Hutt Street are the proud owners of a brand new Heidelberg Spectralis OCT and Heidelberg Edge Perimeter for visual field testing. This state-of-the-art OCT technology enables your optometrist to obtain incredibly high-quality images at significantly increased speeds. The Heidelberg Spectralis OCT has a scan rate of 85,000 Hz and additional eye-tracking technology also improves the precision and repeatability of these scans. This is particularly important when monitoring patients for subtle changes over a long period of time. Together with the visual field information, your optometrist can assess the structure and function of your retina and peripheral vision with increased accuracy of diagnosis. These features are especially beneficial for providing a more complete picture of glaucoma management and can impart better education and understanding for you, the patient.

The ‘Structure-Function’ map of the Spectralis OCT + Heidelberg Edge Perimeter (Visual Field Test).

OCT and Posterior Eye Disease

OCT is particularly useful to scan the layers of the retina to look for subtle and sometimes not-so-subtle eye disease. Signs such as swelling of the retina (as seen in the below images), traction from membranes, loss of photoreceptors due to atrophy and intra-retinal bleeding can all be seen in retinal scans. There are many benefits to having an OCT. It enables easier diagnosis of potentially sight-threatening conditions, can help to monitor a condition such as age-related macular degeneration or diabetic retinopathy, speed up a referral to a specialist, and facilitate effective management of conditions such as central-serous retinopathy. OCT is also useful for examining the optic nerve for early signs of glaucoma and other optic neuropathies.

An OCT confirming diagnosis of an epiretinal membrane (ERM) at the fovea. An ERM is a thin layer of cells that constricts and distorts are of the retina responsible for central vision.

At Innovative Eye Care we recommend every patient over the age of 50 should have a baseline OCT scan done of their retina so that we have a reading to compare future results with, should the eye change. Patients should be aware that an OCT scan does not attract a Medicare rebate and extra charges may apply for this service (we are happy to offer this at 50% off for pensioners and students).

The below image shows an OCT scan of one of our diabetic patients who had noticed her vision drop in one of her eyes. She had swelling of the macula (seen as the 'bulge' of her retina), most likely due to a neovascular membrane in the choroid beneath her retina, and required urgent referral to a retinal specialist for treatment. The 3D image can be used to show you the areas that are affected.

OCT showing swelling at the macula.

3D image showing swelling of the macula.

OCT and Contact Lens Practice

Optical Coherence Tomography has primarily been used by optometrists and ophthalmologists in the examination of the posterior pole, macula and optic nerve head. As OCT becomes a more regular feature in optometry practices, more equipment suppliers are bringing new models to our shores. Many of the latest OCTs, although primarily designed for imaging the posterior segment, are capable of both anterior and posterior eye segment imaging.

With the ability to image the cornea, limbus, sclera, anterior chamber and contact lenses on eye, OCT is an invaluable tool in contact lens practice. Scan width, depth, resolution and mapping options for the anterior segment vary between commercially available OCTs. Some OCTs use Scanning Laser Ophthalmoscopes (SLO) rather than infrared to directly view the fundus and anterior chamber. In contact lens practice, SLO is a bonus addition to OCT as it gives amazing viewing of the tear film and contact lens surface.

OCT can be used for the examination and imaging of thickness and fitting characteristics of soft contact lenses, in particular high plus, high minus and toric lenses. Soft contact lens edge profiles can be assessed and lens-edge interactions with the sclera accurately visualised to better understand how the lens fits on the eye. Lens thicknesses can also be visualised and assessed, as well as the presence and degree of any prism ballasts used to stabilise toric lenses on the eye.

OCT of soft lens showing edges and the thicker ballast used to stabilise toric lenses.

In speciality contact lens modalities such as RGP, ortho-k, miniscleral, scleral and hybrid contact lens fitting, OCT imaging adds another dimension to the examination, specification, and management. In recent years the fitting of miniscleral and scleral RGP contact lenses has become more popular in contact lens practice. Rather than solely using keratometry data, many miniscleral and scleral lens designs use sagittal height to calculate lenses. While biomicroscope techniques and corneal topography can calculate corneal sagittal height and anterior chamber depths with reasonable accuracy, OCT can do much more with higher resolution examination and measurement accuracy. Even epithelial thickness can be monitored as it is molded in ortho-k treatment.

The above image shows the thinned cornea of a patient with advanced keratoconus with their new rigid scleral lens vaulting over the fragile tissue.

A hyperopic orthokeratology lens on eye showing the areas of cornea clearance centrally.

In medical contact lens practice where contact lenses may be used in the management of corneal disease or trauma, OCT allows viewing of the contact lens, post lens tear thickness, corneal epithelium, basement membrane, stroma, endothelium, and associated pathology. Conditions where OCT is useful in medical contact lens practice include keratoconus, corneal graft, pellucid marginal corneal degeneration, recurrent corneal erosion, epithelial basement membrane dystophy, Salzmann's nodular corneal degeneration, pterygium and pingueculum. OCT also allows better management of contact lens complications and differential diagnosis of corneal abrasion, microbial keratitis, and other corneal pathologies.

Anterior OCT of a patient's anterior chamber angle in the dark (left) and the light (right). This is an important assessment for anyone at risk of glaucoma.