To help get a correct diagnosis of neuromyelitis spectrum disorder (NMOSD or NMO), you may be referred to an ophthalmologist or a specialist known as a neuro-ophthalmologist. Along with your neurologist, these experts may perform the various eye tests and physical exams you need to get the diagnosis for NMO.
Medical history
At the beginning of an eye exam, your neurologist or ophthalmologist will ask for your medical history and if you have been experiencing any vision problems. During the eye exam, your eye doctor can perform a number of different tests. Based on the results of these tests, your doctor can determine if you need any follow-up vision tests. These tests help evaluate your overall eye health.1
Because NMO is a rare disease, this part of the exam may take some time. You might need to request your medical records from your primary care doctor to make sure your eye specialist (neurologist, ophthalmologist, or neuro-ophthalmologist) has all the information needed to make an informed diagnosis.2
Color blindness test
A screening test that checks your color vision is often performed early in a comprehensive eye exam to rule out color blindness.
Along with detecting hereditary color vision deficiencies, color blindness tests also can alert your eye doctor to possible eye health problems that may affect your color vision.3
Vision tests
Vision tests are used to measure how well you see. This includes things like whether you can see symbols or alphanumeric characters, are experiencing distorted vision, and how wide your field of vision may be.3
A visual acuity test is the standard eye chart exam that measures how well you can see a letter, number, or symbol from a certain distance. The doctor will often have you read lines with each eye individually while the other eye is covered. They may also ask you to read lines with both eyes.3
Pupillary light reaction
This tests your eyes to see how your pupils respond when exposed to bright light. If your eye is affected by NMO and inflammation to the optic nerve (optic neuritis), your pupillary light reaction (PLR) may be abnormal. This is likely due to inflammation or damage of the optic nerve.3
Slit lamp exam
A slit lamp is a microscope with a bright light. Your doctor uses this to see the parts of your eye up close. This device is a key to finding eye disease and assessing the overall health of your eye. Your doctor will use the slit lamp to look at the structures of your eye under high magnification.2
During this exam, you will place your forehead and chin on the front of the instrument. Your doctor will sit on the other side of the instrument and examine the structures of your eye.2
Ophthalmoscopy
A classic symptom of NMO is inflammation of the optic nerve (optic neuritis). Your optic nerve is a bundle of nerve fibers that serves as the highway for signal transmission between your eyes and your brain.3,4
As part of your eye exam, your neurologist or ophthalmologist will use an ophthalmoscope to look for signs of damage to the optic nerve. An ophthalmoscope is a tool that helps visualize the back of the eye and optic nerve. The eye doctor may give you eye drops to enlarge (dilate) your pupils to get a better look at the nerve at the back of your eye.3,4
The optic disk becomes temporarily swollen in about 1 in 3 people with optic neuritis (ON). People who have had ON in the past due to NMO may have a permanently pale optic disk. However, other conditions may also cause this issue, and this is not considered a specific finding for NMO.3
Dilated eye exam
Your ophthalmologist may perform a dilated eye exam. During this exam, eye drops are placed in your eyes to enlarge (dilate) your pupils. This lets light into your eye and allows your doctor to look inside your eye to see your retina, optic nerve, blood vessels, and other structures within the eye. In many diseases, including NMO, there will be changes to these tissues and structures. Without a dilated eye exam, your doctor will not be able to identify these changes.6
Optical coherence tomography
Optical coherence tomography (OCT) is a non-invasive image test that uses light waves to study the back of the eye, called the retina. OCT measures the thickness of the retinal nerve fiber layer (RNFL).The RNFL may be thinned and decreased in those with NMO and optic neuritis.3,5