Uncommon Ophthalmology: Rarest Eye Diseases/Disorders

Revised and Updated by Seth Preston on: January 11th, 2021

For another article on rare diseases, click here.

The human eye, although small, is a vast frontier susceptible to many different ailments and disorders. The complex but vulnerable organ has a myriad of parts that can be affected by many unfortunate diseases. Naturally, there are a few disorders that are more rare than others. We are going to explore the rarest afflictions today.

In the niche market of clinical trials, contract research organizations (CROs) can do full service project management for certain ophthalmic indications. These rare diseases and disorders have a disadvantageous position to hold from the start of enrollment, mainly because the patient pool is incredibly small compared to more common indications. Often, potential cures for these ailments are labeled as “Orphan Drugs”. To learn more about Orphan Drugs, and what classifies as one, we recommend this information by Orphanet.


Anophthalmia and Microphthalmia

Anophthalmia is a disorder where one or both of the eyeballs are abnormally small. Anophthalmia occurs when the patient is born with an absense of one or both eyes. These rare disorders develop during pregnancy. According to research shared by the Center for Disease Control, it’s estimated that “about 1 in every 5,200 babies is born with anophthalmia/microphthalmia in the United States.


Bietti’s Crystalline Dystrophy

This rare disorder, like most on this list, is inherited at birth. The unfortunate ailment affects the individual with crystals developing on the cornea, causing occasional night blindness and visual field obstruction. Bietti’s Crystalline Dystrophy is estimated to occur in 1 in 67,000 people.


Behçet’s Disease

The four most common symptoms of Behçet’s disease are mouth sores, genital sores, inflammation inside of the eye, and skin problems. Inflammation inside of the eye (uveitis, retinitis, and iritis) occurs in more that half of those with Behçet’s disease and can cause blurred vision, pain, and redness. Typically, this disease impacts fewer than 1 in 100,000 people.


Idiopathic Intracranial Hypertension

Around 100,000 Americans have IIH, and the number is rising as more people become obese or overweight. The disorder is most common in women between the ages of 20 and 50; about 5 percent of those affected are men. This disorder is also more prevalent in people with a body mass index (BMI) of 30 or above, or clinically obese.


Retinitis Pigmentosa

RP is an inherited disorder that results from harmful changes in any one of more than 50 genes. Some of the changes, or mutations, within genes are so severe that the gene cannot make the required protein, limiting the cells function. It’s estimated that around 100,000 people in America are diagnosed with Retinitis Pigmentosa.



This disease usually occurs in children younger than 5 years, and may occur in one eye or in both eyes. In some cases, the disease is inherited from a parent. Retinoblastoma is a serious, life-threatening disease. However, with early diagnosis and timely treatment, in most cases, a child’s eyesight and life can be saved. Estimates suggest around 200-300 children in the U.S. are diagnosed with this annually.


Stargardt Disease

Stargardt disease is an inherited disorder of the retina – the tissue at the back of the eye that senses light. This disease could be described as a younger version of AMD. The disease typically causes vision loss during childhood or adolescence, but in some forms, vision loss may not be diagnosed until later as an adult. Researchers estimate anywhere between 1 in 8,000 – 1 in 10,000 are impacted by this disease.


Usher Syndrome

Usher syndrome is the most common condition that affects both hearing and vision. The major symptoms are hearing loss and an eye disorder called retinitis pigmentosa, or RP. Retinitis pigmentosa causes night-blindness and a loss of peripheral vision. Research estimates around 4 – 17 in 100,000 are diagnosed with Usher Syndrome.


Uveal Coloboma

Estimates of this disease range from 0.5 to 2.2 cases per 10,000 births, which makes this a rare case indeed. The cases are hard to catch because uveal coloboma does not always affect how the eye looks from the outside. Uveal coloboma is a significant cause of blindness in newborns.




The eye is a complex organ, and susceptible to a variety of disorders and diseases. The volume and diversity of the rare examples shows just how fascinating and vast the field of Ophthalmology is.

Ophthalmology CRO’s, like Trial Runners, must encourage enrollment of these unique cases to find fast solutions through trials and research.