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Optical coherence tomography (OCT)

By Dr Mark Gorbatov, Summer 2006

Optical coherence tomography (OCT) is a noninvasive, high- resolution method of imaging the retina in cross-section. It allows us to see details within the retina and its relationships to the vitreous and the pigment epithelium, like no modality in the past. Diagnosis can be made more accurately and patients undergoing treatment followed with precision.

Image showing Dr Gorbatov with a patientThe machine is on a desk and controlled by a computer. For the patient, it is a similar experience to having a retinal photograph taken. The eye is not touched during the examination, which can be carried out, if necessary, through a 3 mm pupil. It is comfortable for the patient as the light levels are low and there is no need for an injection. Each scan takes less than 2 seconds and the whole procedure rarely exceeds five minutes.

The resolution of the instrument is approximately 20 mm (laterally) by 10 mm (axially), meaning that a single pixel on the image corresponds to the size of a cell body on histological section. For this reason this technology has been described as optical biopsy. The information that OCT provides is complementary to fluorescein angiography. There are situations in which one is superior and others which require both modalities. Overall the number of fluorescein angiograms performed is reduced.

Image showing a false colour OCT image of a patient with a stage II full thickness macular hole

Above is a colour OCT image of a patient with a stage II full thickness macular hole. The arrows on the right show the retinal thickness. The list of conditions in which the OCT can be used is extremely long, and includes:

Disorders of the vitreomacular interface:

  • Macular hole
  • Vitreomacular traction syndrome
  • Epiretinal membrane

Vascular maculopathies:

  • Diabetic macular oedema
  • Branch and central retinal vein occlusion
  • Juxtafoveal telangiectasia
  • Cystoid macular oedema
  • Age related macular degeneration and other causes of choroidal neovascularisation
  • Central serous chorioretinopathy
  • Postoperative care of retinal detachment patients
  • Differentiating retinoschisis from retinal detachment
  • Imaging the optic nerve and nerve fibre layer in glaucoma and disc swelling
  • Macular hole

OCT definitively differentiates between full thickness macular holes, which respond very well to vitrectomy surgery, and partial thickness defects, which do not. Additionally, it determines whether the vitreous is attached to the edge of the macular hole. This helps to decide whether to peel the internal limiting membrane in macular hole surgery. By scanning the unaffected eye in a patient with a macular hole it is possible to advise them about the risk of developing the condition in the second eye.

Diabetic macular oedema

In diabetic macular oedema, swelling and hence thickening of the retina is the critical manifestation of the pathology. The cross sectional imaging of the OCT measures this. By showing the structure of the thickened retina, OCT identifies patients who are likely to respond well to laser and also those with a component of vitreous traction for whom surgery ought to be considered. When treating this disorder with intravitreal injections of medication, OCT documents the response to treatment and detects recurrence of the disease. This informs decisions about future dosing.

Optical Coherence Tomography is routinely used at MetWest Eye Centre in the diagnosis and management of retinal conditions and the monitoring of glaucoma.

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