What is This Test and Why Do I Need It?

Submited by Cindy P on March 8, 2018

So you’ve had your eye exam and your doctor has requested that you return for additional testing. What are these tests and why are they important? Each type of special testing is a crucial diagnostic tool used by your doctor to screen for or manage a variety of conditions.

Visual Field Testing

Visual field testing measures a person’s full range of vision, notably the peripheral vision. The test pinpoints areas where vision is compromised as well as blind spots. This is achieved by showing patients lights in their field of vision and recording their response when and where they see the light.

There are several reasons why your doctor may have ordered visual field testing. One of most common reasons is to screen for damage caused by glaucoma. Doctors order this test as part of a glaucoma screening or to manage established glaucoma cases. In patients with glaucoma, the optic nerve can become damaged by high eye pressures. This damage appears as loss of peripheral vision, which the visual field test measures. Routine testing helps your doctor monitor the progression of your condition.

Visual field testing has other uses as well. Patients taking certain medications might require routine tests. Autoimmune medications such as Plaquenil can damage the retina and impair vision. Testing can identify the beginning of a problem before symptoms develop.

Thinking of having surgery to correct drooping eyelids? You will likely have a visual field test to determine how much your droopy lids interfere with your eyesight. Patients who are considering corrective eyelid surgery, or blepharoplasty, will take the test once normally and once with their eyelid skin taped up. This will determine how much their vision could improve after surgery. Insurance plans require this test to determine if they will approve the procedure.

OCT Testing

OCT, or optical coherence tomography, is an advanced scan that provides a detailed image of the retina. Waves of light produce a high resolution picture showing distinct layers of the back of the eye. Each area of the retina can be examined and carefully measured. Abnormalities can be studied and measured as well, and observed over time with routine testing. With this technology, your doctor can screen for and diagnose conditions with a great level of accuracy. 

Your OCT results give your doctor valuable information about your optic nerve, macula, and retina. Since OCT testing provides measurements of the optic nerve, your doctor can use these results to screen for damage caused by glaucoma. Glaucoma frequently begins without noticeable symptoms. With early detection, patients can begin a treatment regimen that can help slow the progression of the condition.

The high resolution images provide measurements of the macula, the central area of the retina responsible for sharp, central vision. This helps rule out retinal or macular disease or monitor the progress of an existing condition. Some of the conditions OCT testing helps evaluate include:

  • diabetic retinopathy
  • age related macular degeneration
  • macular pucker
  • macular edema
  • macular hole

With OCT, doctors can identify the correct treatment for the condition and evaluate the patient’s response.


If you have had cataract surgery, you’ll be familiar with the ASCAN. Performed before surgery, the ASCAN provides the measurements of the eye needed for the procedure. Unlike OCT testing, which provides measurements of internal parts of the eye, the ASCAN measures the shape of the surface of the eye. Most importantly, it provides the precise measurements needed to choose the lens implant. Each person’s eyes are unique, so the accurate analysis the ASCAN provides is necessary to ensure the best surgical results possible.

If you are not sure what kind of testing you are scheduled for, call our office at (951) 696-1135.