Iridocorneal Angle Abnormality (ICAA)

Understanding the iridocorneal angle and its impact on eye health

The iridocorneal angle is where the iris and cornea meet at the base of the eye. This angle is crucial because it drains a fluid called aqueous humor, which is produced inside the eye and helps maintain its intraocular pressure. When severe abnormalities are present, fluid drainage can be impaired, leading to a buildup of pressure inside the eye. This increased pressure is known as primary acute glaucoma, a severe eye condition that can cause blindness if not treated promptly. Early detection and treatment of ICAA are essential to prevent glaucoma and protect the vision of Old English Sheepdogs.

The connection between ICAA (severe) and glaucoma

ICAA (Iridocorneal Angle Abnormality) doesn’t cause noticeable symptoms, and the eye pressure is normal, below 20 mmHg. However, in severe cases, it acts like a Trojan horse, predisposing the eye pressure to buildup and causing primary glaucoma. This is because the condition affects the drainage angle of the eye, which doesn’t directly impact vision in the early stages. Primary glaucoma, a potential consequence of ICAA, causes a variety of symptoms.

Testing for ICAA in Old English Sheepdogs using gonioscopy

Early detection of Iridocorneal Angle Abnormality (ICAA) is essential for maintaining the vision of Old English Sheepdogs. A specialized exam called gonioscopy helps identify this condition. During gonioscopy, an ophthalmologist uses a special contact lens to examine the iridocorneal angle, the drainage area at the front of the eye. Regular eye exams typically don’t include gonioscopy, so if your dog has had a normal eye exam with the result “eyes clear,” it means the dog is free from issues like cataracts, PRA, entropion, etc.

An ophthalmologist in Norway performs gonioscopy to an Old English Sheepdog who tested ICAA-free.

Scheduling gonioscopy in your dogs life

Because ICAA often develops later in life, it is recommended to schedule your dog’s first gonioscopy at one year of age. A dog that tests negative for ICAA at this young age may still develop the condition later in life. If the initial exam shows no signs of ICAA, it is advised to conduct gonioscopy every three years, at ages four and seven. However, dogs diagnosed with ICAA will require more frequent examinations, as determined by the ophthalmologist, to monitor any progression. By testing your dogs before breeding and making informed breeding decisions, you can effectively manage the risk of glaucoma.

What does the ophthalmologist look for during gonioscopy?

When your ophthalmologist performs a gonioscopy, they will look for two key things: the irido-corneal angle width (ICA)  and the pectinate ligament (PL).

Angle Width: Its impact on eye fluid drainage

The angle width can be normal (open), narrow, or closed. A normal angle allows for proper drainage of eye fluid, while narrow or closed angles can cause drainage problems, increasing the risk of glaucoma.

Pectinate Ligament: Crucial for proper eye drainage

The pectinate ligament functions like a tea strainer; if the holes are too small, they can easily become blocked, leading to acute glaucoma. This tiny structure drains fluid (aqueous humor) from the eye. The veterinarian will check the shape of the pectinate ligament and how the fibers are spaced. If the fibers are too large or too close together and the openings for the passage of aqueous humor are too small, this is referred to as dysplasia of the pectinate ligament (PLA in the ECVO certificate and PLD in the ACVO certificate).

The assessment of the angle width (ICA on the certificates), along with the condition of the pectinate ligament, helps determine the grade of ICAA (mild, moderate, or severe).

From June 2024, our breed is on the list requiring ophthalmologists to perform gonioscopy during regular eye exams for ECVO certification.

Categorizing ICAA severity by grading schemes

Knowing the severity of your Old English Sheepdog’s ICAA is crucial for both their current and future health. While various grading schemes exist, most categorize ICAA as mild, moderate, or severe. Let’s explore what each grade signifies and the recommended course of action:

• Mild ICAA (Grade 3)

  • Normal (open) angle with minor abnormalities in the pectinate ligament
  • Low risk of glaucoma
  • Next checkup on the advice of the ophthalmologist to verify if the condition progresses to moderate or severe ICAA
  • Breeding only with an ICAA-free (unaffected) partner

• Moderate ICAA (Grade 2)

  • Open or narrow angle with more significant abnormalities in the pectinate ligament
  • Medium risk of glaucoma
  • Next checkup on the advice of the ophthalmologist to verify if the condition progresses to severe ICAA
  • Breeding only with an ICAA-free (unaffected) partner and advise to test offspring for ICAA

• Severe ICAA (Grade 1)

  • Narrow or closed angle with severe abnormalities in the pectinate ligament
  • High risk of glaucoma
  • Regular eye-pressure check to ensure that’s always below 20 mmHg and need for preventive medical therapy
  • No breeding

ICAA testing and grading systems across regions

There is a standard test method (Gonioscopy) for determining the grade of ICAA, but various forms exist for recording the results. Let’s start with the most common form in Europe, used by the EVCO. The EVCO has made testing for ICAA mandatory for our breed, integrating it into the regular eye exam. The results are published on the same form that lists Cataract and other eye defects. In Europe, we use a grading system of mild, moderate, and severe.

An example of the EVCO eye certificate. Click to enlarge this image.

EVCO is not present in all European countries. In Eastern Europe, EESVO (East European Society of Veterinary Ophthalmology) also tests for ICAA. On their certificates, the condition may also be referred to as goniodysplasia.

In the United States and Canada, the AVCO uses a separate form for grading ICAA. They use a system ranging from 4 (free) to 1 (severe).

An example of the ACVO/OFA Gonioscopy Exam form. Click to enlarge this image.

Ensuring comprehensive gonioscopy for your dog

In addition to ophthalmologists who are part of large Veterinary Societies, some ophthalmologists could operate independently. If you plan to have gonioscopy done for your dog, it is important to ensure that your ophthalmologist checks both the angle width and pectinate ligament. A complete ICAA result cannot be obtained if one of these is not examined.

The unclear inheritance of ICAA in Old English Sheepdogs

The exact inheritance pattern of ICAA in Old English Sheepdogs remains a puzzle. It’s not part of the Multi-Ocular Defect (MOD) complex, and an ICAA-affected dog can even be MOD-free. Currently, there are no DNA tests available specifically for detecting ICAA in Old English Sheepdogs.

Research efforts at the University of Cambridge

Researchers at the University of Cambridge in the UK are striving to identify the genetic mutations responsible for ICAA in Old English Sheepdogs, with the aim of developing a DNA test. They believe that multiple genes may be involved in this condition. Building on their success with a similar test for Border Collies, the researchers are making significant strides in this area. However, their progress is currently hindered by the challenge of collecting sufficient DNA samples, particularly from dogs older than four years. Collecting these samples remains a significant obstacle.

The potential impact of a DNA test

A reliable DNA test for ICAA would be a game-changer for breeders, enabling early detection and preventative breeding strategies. Although a dog might test free of ICAA at one year old, it can still develop the condition later in life. Since it’s impractical to breed only with dogs older than four years (when their ICAA status becomes more stable), genetic testing becomes the optimal solution.

How you can help finding the mutation for ICAA

If you want to get involved with this research or donate DNA, please follow this link.  It’s important to know that the DNA needed must come in pairs from an ICAA-affected dog and an unaffected littermate (or from dogs with the same parents). Since ICAA progresses over the years, older dogs are preferred as their condition is more stable and informative for the research.

Managing ICAA in Old English Sheepdogs: prognosis and tips

The outlook for Old English Sheepdogs with ICAA varies depending on the severity. Here’s a closer look.

Monitoring mild to Moderate ICAA (Grades 3-2)

The prognosis for these dogs is generally good. They face a lower risk of glaucoma compared to those with severe ICAA. However, regular veterinary checkups remain crucial to monitor eye pressure and catch any potential issues early. For mild ICAA (Grade 2), immediate treatment is usually not required, but regular monitoring is essential to detect any progression to moderate or severe ICAA. Moderate ICAA (Grade 1) necessitates regular eye exams and eye pressure control to ensure it doesn’t progress to severe ICAA.

Managing severe ICAA (Grade 1)

Severe ICAA poses a significant risk of developing glaucoma, making close veterinary monitoring essential. The key to managing severe ICAA is to prevent glaucoma before it starts. This involves keeping intraocular pressure (IOP) very low through preventive therapy, such as eye drops. These eye drops work by reducing the production of aqueous humor, the fluid inside the eye. In dogs with severe ICAA, preventive eye drops are recommended even if the IOP is within the normal range. This is because maintaining the lowest possible IOP helps prevent the development of glaucoma. While severe ICAA doesn’t always lead to glaucoma, early intervention is crucial.

Safeguarding vision in Old English Sheepdogs

Early detection is crucial in protecting your Old English Sheepdog’s vision from ICAA. Since this condition often develops later in life, schedule the first gonioscopy exam at one year old, followed by regular checkups every three years (at ages four and seven) to ensure timely intervention if necessary.

Importance of testing before breeding

It’s important to understand that dogs testing free of ICAA at a young age can still develop the condition later in life. Therefore, when breeding dogs with mild or moderate ICAA (Grades 3-2), it is crucial to ensure their partners are truly ICAA-free (unaffected). This can be achieved by testing the partner’s parents or confirming the partner’s ICAA-free status at an age when the condition is unlikely to develop further.

By integrating ICAA testing into your breeding practices and prioritizing responsible breeding choices, you can significantly impact the well-being of future Old English Sheepdog generations.