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WHAT IS OCT?
OCT stands for Optical Coherence Tomography. It is a non-invasive imaging test that uses low-coherence light waves to take cross sectional pictures of the retina of your eye. With OCT, your ophthalmologist can see each of your retina’s distinctive layers which allows him to map and measure their thickness. These measurements help to diagnose various eye problems with great accuracy and sensitivity. He compares the measured thickness of the retinal layers of the patient’s eyes with the normal thickness of the healthy retinal layers to determine which retinal disease or eye problem exists in the eye. They also help in detecting the early onset and treatment guidance of glaucoma and diseases of the retina. These retinal diseases include age-related macular degeneration (AMD) and diabetic eye disease. OCT also helps to detect any changes in the fibres of the optic nerve.
HOW IS OCT CARRIED OUT?
OCT is nothing but similar to ultrasound except the fact that OCT uses light waves instead of sound waves. It is like the CT scan that scans and examines various internal body parts of the patient. Here, the OCT scan deals solely with the eyes.
For OCT, the patient simply sits in front of a machine and places his/ her head as directed. Within no time, the technician completes the process and has the pictures of the patient’s eyes. For carrying out this procedure, dilating eye drops are first applied to the eyes. This keeps the eyes sensitive to the light for several hours after the test. A camera like device then directs light waves which bounce back with an accurate 3-D picture of the patient’s eye structure. The pictures show the retina, the optic disk, and the blood vessels.
WHEN IS OCT SCAN RECOMMENDED?
In most of the cases, OCT scan is referred to the people with an age of 25 or more. Doctors may also recommend OCT scan to a patient if they suspect the possibility of the patient having any one of the following diseases or conditions:
- Diabetes
- Macular Degeneration
- Glaucoma
- Retinal Toxicity
Carrying out the OCT scan helps the doctor to keep a track of what’s going on beneath the surface of the patient’s eyes.
Even if any of the above diseases are not suspected in the patient’s eyes, OCT scan should be performed before carrying out major eye operations or surgeries in order to prevent any complications in future. Carrying out surgeries without properly examining the eye for any such conditions can pose threat to the patient’s eye health.
Among many eye problems, eye cataract is a condition in which the eye lens becomes opaque and hence the vision of the person becomes blurry. The ultimate treatment for cataract is the cataract surgery.
Before taking the patient for the surgery, it is important to make sure that the patient is free from any other eye problems except cataract.
OCT is not compulsory for carrying out cataract surgery. OCT is not a part of the surgery and therefore the surgery can successfully be performed and completed without having a look at the retinal images of the patient. But, it is advised to go for the OCT scan before the surgery for good and valid reasons as discussed in the next section.
WHY SHOULD “OCT” BE PERFORMED BEFORE CATARACT SURGERY?
There are two distinct areas in the eye that should be carefully examined before the cataract surgery: the macula and the periphery.
Peripheral retinal pathologies can increase the chances of retinal detachment after the cataract surgery. OCT scan should be performed with a dilated pupil to check for any retinal disorder. If any retinal breaks are detected, they should be treated with laser before the surgery itself. The macula, on the other hand, may hide a large number of pathologies that are not visible through normal scanning tests and can only be observed through OCT scan.
Performing an OCT scan of the retina is quick, safe and easy both for the patient and the technician.
Here are a few reasons to use OCT to check the retina of every patient prior to cataract surgery.
1.Many retinal diseases can only be detected with OCT.
Many types of retinal diseases are simply invisible through a microscope. These are visible only through an OCT scan. (In addition to this, the presence of the cataract may increase the difficulty of visualizing the condition of the macula.) Detection of such type of diseases before the surgery is important so that the condition does not worsen during the surgery.
2.If the doctor does not check well for all the eye problems before the surgery, everyone will assume that the cataract surgery caused it.
If the doctor finds any eye problem in the macula or the peripheral retina before the cataract surgery, it’s called a pre-existing condition. But regardless of the cause of the problem, if it’s found after the cataract surgery, it will be considered a complication caused during the surgery. That will be the case even if the cataract surgery didn’t cause it.
3.In most cases, cataract surgery isn’t performed by a retinal specialist.
If the surgeon is not a retina specialist, he is less likely to be checking carefully for retinal problems that aren’t obvious or whose symptoms are not clearly visible to him. He’ll also have less training and knowledge of macular disease. Hence, he will carry out the surgery assuming the patient’s eye to be free from all sorts of retinal diseases (even if it’s not).
4.Most of the pre-operative exams are done in a hurry, with the prime focus of the experts being on getting the refractive error correction right.
Before taking the patient for surgery, the doctors and the staff make every possible measurement so that the refractive error correction comes out correctly. What if they make every possible measurement and the refractive outcome is also perfect, but the patient can’t see well (because of some existing eye problem that has not been found)? This situation can be improved by using OCT before the cataract surgery.
WHAT IMPORTANT PRECAUTIONS NEED TO BE TAKEN IN ORDER TO MAKE THE MOST OF OCT?
- Pseudo -colour algorithms (i.e., colour encoding), thickness maps or 3-D mapsshould never be used.
- Make sure the doctor examines every black and white slide of the scan carefully.
- While examining the images of the scan, the presence of drusen should not be confused with macular degeneration. The presence of drusen does have some consequences, but it is not necessary for those consequences to include macular degeneration.
- Make sure that the patient’s eyes are dilated before performing the OCT.
- If any macular disease is found, a multifocal IOL should not be implanted.
- If the patient is taking anti- VGEF injections, the surgery should be scheduled in such a manner that it does not disturb the schedule of the injections.
- If the eye has an epimacular membrane, the order in which the surgeries are performed should depend on the grade of cataract.
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