What is synechia of the eye?
Synechiae are abnormal adhesions (attachments) that form within the eye, often affecting vision and overall eye health. This condition typically occurs when the iris, the colored part of your eye, sticks to other structures, such as the lens or cornea.
Some types of synechiae can affect the appearance and movement of your pupil. Other types can block normal fluid flow, preventing the eye from functioning properly. During an eye exam, your doctor can determine the location of the adhesions.
While all synechia types can affect your vision, some synechiae pose more serious risks to your eye pressure and overall eye health than others.
What causes synechiae to form?
Synechiae can develop in the eye when inflammation, injury or high pressure causes parts of the inside of your eye to stick together.
Inflammation is a common cause of synechia. It is your body’s natural healing response to infection, disease or other trauma. During inflammation, the body releases immune cells and proteins. These substances can accumulate and cause structures in the eye to stick to one another. Scar tissue can develop between the membranes of the structures, leading to strong adhesions.
What is the difference between synechia and synechiae?
The term "synechia" is singular and refers to a single adhesion. The term "synechiae" is plural and refers to multiple adhesions.
Types of ocular synechiae
The type of synechia in the eye is based on the location of the abnormal adhesions and the eye structures involved. These structures include the:
- Cornea – This is the clear, dome-shaped protective layer covering the front of the eye.
- Iris – This is the colored part that surrounds the pupil and controls how much light enters the eye.
- Lens – This is the transparent structure behind the iris that focuses light rays on the light-sensing tissue (the retina) at the back of your eye.
- Drainage angle – This is the location where fluid drains from the eye, helping control eye pressure (also called intraocular pressure or IOP). It is located at the junction between the iris and cornea.
The main categories of synechia are:
- Anterior synechia – Adhesions between the anterior iris and cornea (at the front of the iris where it meets the cornea)
- Peripheral anterior synechia – Adhesions in the periphery between the anterior iris and cornea, at the junction that forms the drainage angle of the eye
- Posterior synechia – Adhesions between the posterior iris and lens (at the back of the iris where it is adjacent to the lens)
Anterior synechiae
Anterior synechiae occur when there are adhesions between the front surface of the iris and the back surface of the cornea. They are usually the result of:
- Inflammation – Caused by eye diseases like uveitis and iritis (discussed below)
- Trauma – Caused by injuries, often from accidents or sports
When anterior synechiae form, they can affect your eyes in several ways:
- Irregular pupil – The pupil might appear irregular or not respond normally to light changes. This is because the iris controls the pupil, and it is stuck to the cornea.
- High eye pressure – Intraocular pressure may rise if adhesions occur where the iris meets the cornea at the drainage angle.
Anterior synechiae around the drainage angle are called peripheral anterior synechiae (PAS). The drainage angle is where a nourishing fluid, called aqueous humor, exits the eye. If this fluid flow is blocked, it can lead to a type of glaucoma called angle-closure glaucoma.
PAS can result in increased eye pressure and potentially damage the optic nerve, which connects the eye to the brain. This can lead to permanent vision loss.
Posterior synechiae
Posterior synechiae occur when there are adhesions between the back surface of the iris and the front surface of the lens. This is the most common type of synechia. It can occur in individuals with uveitis or iritis.
Uveitis is a condition in which the middle layer of the eye, known as the uvea, becomes inflamed. Iritis, or anterior uveitis, is inflammation of the iris. The iris is part of the anterior uvea. Anterior uveitis can cause symptoms such as:
- Eye pain
- Eye redness
- Sensitivity to light
- Blurry vision
- Irregular pupil
Some people have a gene variant called HLA-B27. This variant increases their risk for certain inflammatory and autoimmune conditions. When someone with HLA-B27 gets uveitis, it usually leads to more severe inflammation. This increases the risk of complications like posterior synechiae. HLA-B27-related uveitis is associated with conditions such as:
- Inflammatory bowel disease
- Psoriatic arthritis
- Ankylosing spondylitis
When inflammation occurs, proteins and inflammatory cells may cause the iris to adhere to the lens in a complete ring around the pupil. This is called seclusio pupillae.
This can block the flow of aqueous humor from the posterior chamber (behind the iris) to the anterior chamber (in front of the iris). Pressure can build up behind the iris, causing it to bow forward. This forward bowing, known as iris bombe, can push the peripheral iris against the drainage angle. This can lead to angle-closure glaucoma.
Causes and risk factors
Synechiae can develop when adhesions or scar tissue form between the iris and the cornea or lens.
They may form in the eye through two different processes:
- During inflammation – The immune system sends repair cells and proteins to damaged areas. Sometimes, these substances cause adhesions between structures that should stay separate.
- Through mechanical contact – A force on the iris, such as from trauma or pressure changes inside the eye, can push it against other structures. This can cause adhesions to form.
Finding the underlying cause helps doctors choose the right treatments. It also helps them manage related conditions better, including:
- Uveitis (anterior uveitis/iritis)
- Eye injuries
- Infections
- High eye pressure
- Autoimmune diseases, such as those associated with HLA-B27
- Complications from surgery
- Congenital disorders (those present at birth)
- Cataracts
- Tumors
- Idiopathic conditions (of unknown cause)
Symptoms of eye synechiae
The symptoms of synechiae can vary depending on where the adhesions form and how extensive they are. Common symptoms include:
- Changes in the pupil (irregular shape or abnormal response)
- Decreased vision
- Eye pain or pressure sensation
- Eye redness
- Watery eyes
- Light sensitivity
When to seek medical care
Some symptoms are a sign that you require urgent treatment. Prompt care can prevent lasting damage. Seek care immediately if you experience:
- Severe eye pain
- Sudden vision loss
- Seeing halos around lights
Halos can signal high eye pressure, especially if you also have nausea or vomiting. These symptoms combined can indicate angle-closure glaucoma. If this happens, it’s important to seek medical help to prevent vision loss.
Symptoms of uveitis, often associated with synechiae, may last only a short time (in acute cases) or recur frequently and persist for a long time (in chronic cases). Sometimes, symptoms can appear suddenly and worsen rapidly. Work with your doctor to understand your risk of developing synechiae and the potential complications.
Complications of eye synechiae
When synechiae form inside the eye, they can lead to a range of problems that affect the eye. Some of these complications will require urgent treatment or close monitoring, including:
Angle-closure glaucoma
A serious complication of synechiae is angle-closure glaucoma. This can develop when adhesions block the eye's drainage system. This condition can lead to dangerous spikes in eye pressure. Permanent damage can occur if it is not treated quickly.
Iris bombe
When posterior synechiae form a complete ring around the pupil, they can create iris bombè. The iris bulges forward, blocking fluid flow inside the eye and causing pressure to build up rapidly. Iris bombe requires immediate treatment to prevent permanent damage.
Early treatment often prevents complications and preserves vision. This means it is important not to wait until symptoms worsen. Your eye doctor can determine whether your symptoms indicate synechiae or another condition that needs treatment.
Diagnosis and tests
Accurate and early diagnosis of ocular synechiae is essential. This typically begins with a comprehensive eye examination that includes:
- Visual acuity testing – Checking for vision changes with eye charts
- Tonometry – Checking the pressure inside your eye
- Visual field testing – Checking peripheral vision
Eye doctors use various exams and instruments to diagnose adhesions and their causes. These include:
Slit lamp exam
Diagnosing synechiae begins with a thorough eye exam. During the exam, your doctor will use a specialized microscope called a slit lamp. This helps them examine the structures inside your eye.
Gonioscopy
A procedure called gonioscopy may be needed to examine the drainage angle of your eye. During gonioscopy, your doctor uses a special lens that is placed on the cornea after it is numbed with drops. This allows them to see parts of your eye that aren't visible during a regular examination. This helps identify synechiae that might be blocking the drainage angle.
Anterior segment optical coherence tomography
Advanced imaging techniques, such as anterior segment optical coherence tomography (ASOCT), may be used. ASOCT can provide detailed images of the internal structures of the eye.
These scans help your doctor see exactly where adhesions have formed and how they're affecting fluid flow inside your eye. ASOCT is a painless procedure that takes only a few minutes.
READ MORE: Understanding optical coherence tomography (OCT)
Treatment options for ocular synechiae
Treatment for ocular synechiae includes breaking apart existing adhesions. It also includes addressing the underlying cause to prevent further damage to the eye. Synechiae can arise from various conditions and differ in severity. For this reason, the treatment plan is individualized for the specific type of synechia.
Medications
The following medications can help manage synechiae, especially when inflammation is the underlying cause:
Mydriatic eye drops
Mydriatic eye drops, also known as cycloplegics, work by dilating (enlarging) your pupil. They work by relaxing the muscles within your iris. This can help break apart fresh adhesions by gently pulling the iris away from the lens. It can also help stop new posterior synechiae from forming. You may experience temporary blurring of your vision while using mydriatic drops.
Corticosteroid medication
Corticosteroids may be used when synechiae are caused by inflammatory conditions, such as uveitis. These drugs help reduce swelling and irritation, which can help prevent adhesions from forming.
Glaucoma medication
If synechiae cause high eye pressure or glaucoma, your doctor might prescribe glaucoma medications. These can lower the eye pressure and protect the optic nerve from further damage.
Surgical interventions
Sometimes, medication isn't enough to manage synechiae or their complications. An ophthalmologist may need to perform surgery.
Laser peripheral iridotomy is a surgical procedure that creates a small hole in the iris. This allows fluid to flow around adhesions that block drainage. This procedure takes only minutes and can prevent dangerous pressure increases.
Prevention and management of eye synechiae
If you have synechiae, it’s crucial to follow your doctor’s treatment plan closely. This typically includes:
- Taking medications as prescribed
- Attending follow-up appointments
- Making any recommended activity modifications during treatment
It’s important to contact your eye doctor promptly if you experience any eye pain or persistent changes in your vision. Attending regular eye exams and following your doctor’s advice will help you maintain the health of your eyes.
