EYE-OCT.(OPTICAL COHERANCE TOMOGRAPHY)

21
EYE-OCT.(OPTICAL COHERENCE TOMOGRAPHY ) Presented by SANJIB PASHI

Transcript of EYE-OCT.(OPTICAL COHERANCE TOMOGRAPHY)

EYE-OCT.(OPTICAL COHERENCE TOMOGRAPHY )

Presented by SANJIB PASHI

Eye + Optical Coherence Tomography =EYE-OCT.

LIGHT CONSTANTPHASE DIFFERENCE

“SLICES”HUMANEYE

What is Optical coherence tomography?

noncontact, noninvasive imaging technique used to obtain high resolution cross-sectional images of the retina and anterior segment.

Three-dimensional imaging technique with ultrahigh spatial resolution

Measures reflected light from tissue discontinuities

Based on interferometry involves interference between reflected

light and a reference beam.

Optical coherence tomography-The process is similar to that of ultrasonography, except that light is used instead of sound waves. 

Analog to ultrasound

Principle of OCT

Interferometry is the technique of superimposing (interfering ) two or more waves, to detect differences between them.

Interferometry works because two waves with the same frequency that have the same phase will add each other while two waves that have opposite phase will subtract.

Principle of OCT

Light from a source is directed onto a partially reflecting mirror and is split into a reference and a measurement beam.

The measurement beam reflected from the specimen with different time delays according to its internal microstructure.

Principle of OCT

The light in the reference beam is reflected from a reference mirror at a variable distance which produces a variable time delay.

The light from the specimen, consisting of multiple echoes, and the light from the reference mirror, consisting of a single echo at a known delay are combined and detected.

Different kind of OCT.

Time domain OCT

Frequency domain OCT (FD-OCT)

Spatially encoded frequency domain OCT (spectral domain or Fourier domain OCT)

Time encoded frequency domain OCT (also swept source OCT)

Why we need OCT.?

Measles infections can harm the front or back of the eye, possibly causing vision loss or blindness

Six Ways Measles Can Affect the Eyes

Conjunctivitis: Redness and watery eyes from conjunctivitis occur in nearly all measles patients.  This type of pink eye usually develops early on in the disease and is a hallmark symptom along with fever, cough and a runny nose, often occurring before the telltale rash.

Keratitis: Keratitis is an infection of the cornea, the window of the eye. In comparison with conjunctivitis, keratitis has more severe symptoms and far more dangerous consequences. Symptoms include pain, redness, tearing and light sensitivity. It can feel as though foreign particles are lodged in the eye.

Corneal scarring: Corneal ulcers are open sores on the front of the eye that can occur when infected, either via the measles virus or from a bacterial infection that develops secondary to measles.

Six Ways Measles Can Affect the Eyes

Retinopathy: While rare, there are documented cases where the measles virus destroys the retina, a layer of cells in the back of the eye that convert light energy into electrical impulses that go to the brain.

Optic neuritis: This inflammation affects the optic nerve that sends signals from the back of the eye to the brain. This complication is relatively rare but can occur in measles patients who also develop encephalitis, or brain swelling, though cases without encephalitis have also surfaced. Acute cases may be treated with corticosteroids. Like retinitis, vision loss from optic neuritis can be temporary or permanent. Blindness: Measles is a leading cause of childhood blindness in developing countries where immunization programs for this disease are less established or often interrupted by conflict. When compounded by malnutrition, particularly vitamin A deficiency, measles is associated with corneal scarring from ulceration and keratitis, two of the most likely reasons for blindness from measles. Blindness from optic neuritis has also been noted.

OCT. scan procedure of retinas

Regions

For purposes of analysis, the OCT image of the retina can be subdivided vertically into four regions the pre-retina the epi-retina the intra-retinathe sub-retina

Anomalous structures

pre-retinal membraneepi-retinal membraneVitreo-retinal strandsvitreo-retinal tractionpre-retinal neovascular membranepre-papillary neovascular membrane

A pre-retinal membrane with traction on the fovea

Preretinal macular fibrosis has been variously termed by various investigators as surface wrinkling retinopathy, cellophane membrane or cellophane maculo pathy, preretinal traction membrane, macular pucker etc.

a pigment epithelial detachment is causing the convexity

The outer segments of the photoreceptors receive oxygen and nutrition from the choroid. If the retina is detached from the choroid, the photoreceptors will fail. The fovea has no retinal blood vessels and depends wholly on the choroid for its oxygen, so detachment of the macula leads to permanent damage to the cones and rods at the posterior pole, and loss of vision. 

Macular cyst

A cyst caused by vitreous traction in the macula, the tiny oval area made up of millions of nerve cells located at the center of the retina responsible for sharp, central vision.

Macular hole

The center of the macula is the fovea. Foveal cysts are caused by vitreous traction. Eyes that develop foveal cysts may remain stable, develop full-thickness macular holes

Serous retinal pigment epithelial detachment (PED)

A serous pigment epithelial detachment occurs when the sensory retina detaches from the pigment epithelial layer due to inflammation, injury, or vascular abnormalities. A serous pigment epithelial detachment often occurs in conjunction with central serous chorioretinopathy. This is because of the fluid that accumulates in the subretinal space.

Scanning Tips

Minimize patient fatigue by keeping scan time to a minimum.  Never scan an eye for more than 10 minutes

Keep the cornea lubricated.  Use artificial tears and have the patient blink when you are not saving a scan pass.

Reflectivity may be further enhanced by moving the focus knob on the side of the OCT unit