How Terrien’s marginal degeneration changes your vision
The cornea is the clear front window of the eye. In Terrien’s marginal degeneration, a band near its outer edge slowly thins. Blood vessels grow into the thinned area, and fatty deposits collect along its leading edge.[4] As the edge thins, it changes the curve of the whole cornea.
That change shows up as astigmatism, often the against-the-rule kind (the cornea is steeper side to side than top to bottom).[2] Early on, glasses may correct it. As the thinning progresses the astigmatism grows and becomes more irregular, and blurred vision is a common reason people seek care.[1][5] Some people also have red, irritated eyes. In the Canadian series, 56% of patients had inflammation of the eye surface when they first came in.[2]
It is rare. One hospital network in India diagnosed Terrien’s in 184 of nearly 2.5 million new patients over eight years.[3] It is more common in men, often in middle age,[1] and it usually affects both eyes, unevenly.[2] In a Canadian series of 25 patients the average age at first visit was 44, and 72% had it in both eyes.[2] A Nordic study found it was diagnosed at any age between 15 and 86.[4]
It usually moves slowly. In the Canadian series, astigmatism increased on average by 1.68 diopters over three years.[2] A Finnish study that followed 16 patients for a median of seven years found two patterns. Most changed very slowly. A subgroup progressed faster, and only in that subgroup did the thinnest point of the cornea fall below 450 microns.[5]
Perforation is uncommon but possible. In the Canadian series, 5 of 43 eyes perforated, four of them without any injury.[2] In the Indian hospital series it was 2 eyes, under 1%.[3] The Finnish study described perforations that caused no symptoms at all, and noted that the changes at the edge of the cornea tend not to be felt.[5] That is why regular checks with imaging matter even when your vision seems stable.
How a scleral lens works in Terrien’s
A scleral lens is a large rigid gas-permeable lens. It rests on the sclera (the white of the eye) and arches over the entire cornea, including its thin edge, without touching it. Before insertion it is filled with sterile saline, so a layer of fluid sits between the lens and the cornea.
The fluid fills in the cornea’s warped shape. Light passes through the smooth front of the lens and an even layer of fluid, which largely cancels out the irregular astigmatism. A case report describes this as masking the irregularity with a layer of fluid to give a smooth surface.[7]
The size of the lens helps here. A small rigid lens has to sit on the cornea, and when the thinning is at the edge, it has a hard time finding a stable, comfortable place to rest. Corneal rigid lenses can give good vision but fit poorly in advanced stages of these thinning conditions.[7] A scleral lens clears the thin area entirely.
The edge of the cornea is also where the lens’s landing zone sits, though. In Terrien’s, growths such as pseudopterygium (a fold of tissue that grows onto the cornea) and raised areas near the edge can make lenses hard to tolerate, and they need extra consideration when the lens is designed.[6]
What the research shows
The evidence for scleral lenses in Terrien’s is a few small case series and case reports. There are no comparison studies.
- A case series of six eyes in four patients with advanced Terrien’s found vision improved in all six with a custom scleral device (PROSE). Every patient had tried at least one other type of contact lens first. People with growths or bumps near the edge of the cornea also gained vision, comfort, and lens tolerance. Two eyes were held back by other eye problems unrelated to the cornea. One eye stopped wearing the device because a problem with the cells at the edge of the cornea got worse and needed a transplant of those cells.[6]
- A case report of a person with both keratoglobus and Terrien’s showed that a scleral device can be fitted successfully. It needed changes to the lens’s height, landing zone, and size, plus imaging to follow corneal swelling over the day.[7]
- Reviews list scleral lenses among the non-surgical options for Terrien’s, with surgery reserved for very thin corneas.[1][8]
These reports suggest scleral lenses are worth trying when glasses and smaller lenses no longer give good vision. They can’t tell you how likely success is for your eye.
Other options, compared
Glasses work for many people in the earlier stages. Rigid gas-permeable lenses and scleral lenses are the main non-surgical options as astigmatism increases.[1] When the cornea becomes very thin, at or below about 150 microns, a review advises that surgery such as a graft to reinforce the edge may be needed.[1] Surgery isn’t a cure. In the Canadian series, eyes that needed surgery had poorer vision before and after it,[2] and the Finnish study saw thinning continue after grafting in some patients.[5]
| Option | What it does | Typically suited to |
|---|---|---|
| Glasses | Correct regular astigmatism | Early or slowly changing disease |
| Soft toric lenses | Correct regular astigmatism on the eye | Mild, mostly regular astigmatism |
| Corneal rigid gas-permeable lenses | Give a smooth optical surface on the cornea | Moderate astigmatism where the lens centers and is comfortable |
| Scleral lenses | Vault the whole cornea, including the thin edge, over a fluid layer | Irregular or high astigmatism, or failure of the options above |
| Lamellar or patch graft | Reinforces the thinned edge with donor tissue | Severe thinning or risk of perforation |
Questions to ask a scleral lens fitter
- Have you fitted scleral lenses on Terrien’s or other conditions that thin the edge of the cornea?
- Where will the lens rest, and will any growths or bumps near my cornea get in the way?
- Will you work with my cornea specialist on monitoring the thinning?
- How will we tell whether a change in my vision is the lens or the disease?
- How many visits does a fit usually take, and what do the fees cover?
- Do you bill my insurance directly, or give me a superbill to submit myself?
- What signs mean I should remove the lens and call you the same day?
Common questions
Is Terrien's the same as pellucid marginal degeneration?
No. Both thin the edge of the cornea, and both need telling apart from other conditions that thin the edge, such as Mooren's ulcer. In Terrien's, the thin area typically has blood vessels growing into it and fatty deposits along its leading edge. Your cornea specialist makes the diagnosis.
Will Terrien's make me go blind?
It usually progresses slowly, and many people keep useful vision for years. In a Nordic study of 29 patients, median vision with glasses was 20/25. A small number of eyes thin enough to perforate, which is why regular checks matter.
Can I wear a scleral lens if I have a growth on the white of my eye near the cornea?
Sometimes. Growths called pseudopterygia, and other bumps near the edge of the cornea, can make lenses uncomfortable and need extra care in the fit. In a small series, people with these problems still did well with a custom scleral device. Your fitter will look at exactly where the lens would rest.
Do I need to stop wearing lenses if my eye gets red and sore?
Remove the lens and call your eye doctor. Some people with Terrien's have flare-ups of inflammation that need treatment, and a red, painful eye can also mean a problem with the lens. Your doctor needs to check which it is.
When is surgery needed?
Surgery is usually kept for when the cornea becomes very thin or perforation looks likely, or when glasses and lenses can no longer give useful vision. It typically uses a graft of donor tissue to reinforce the thin edge.