Pectinate Ligament Abnormality

What is pectinate ligament abnormality/goniodysgenesis?

The pectinate ligament sits at the drainage angle of the eye, the iridocorneal angle, where fluid leaves the eye. In a normal eye, the ligament is made up of thin, comb-like fibres that allow fluid to drain freely. In dogs with PLA, these fibres are thickened or replaced by sheets of tissue, which can narrow or obstruct the drainage pathway.

Severe obstruction increases the risk of primary closed-angle glaucoma (PCAG), a painful inherited condition that can progress to blindness if undetected and untreated. Gonioscopy allows the ophthalmologist to examine this drainage angle directly and assess the degree of abnormality present.

The 2026 gonioscopy grading change

The BVA gonioscopy grading scheme changed on 1 January 2026. Grade 0 has been retired, and the system now uses three grades instead of four. If your dog was previously graded under the old scheme, here is how the grades compare:

Previously, grading worked as follows: Grade 0 was assigned when 1% or less of the drainage angle was affected. Grade 1 covered 1 to 25% abnormality. Grade 2 covered 25 to 75% abnormality. Grade 3 was assigned when more than 75% of the angle was affected.

From 1 January 2026, the new three-grade system applies: Grade 1 covers 0 to 25% abnormality and is classified as normal or mildly affected. Grade 2 covers 26 to 75% abnormality and is classified as moderately affected. Grade 3 covers 76 to 100% abnormality and is classified as severely affected.

Under the new scheme, the best possible result is Grade 1, not Grade 0. A Grade 1 result means your dog has minimal or no clinically significant abnormality of the drainage angle.

Why was the grading changed?

The change followed representations from breeders and extensive discussion within the BVA Eye Panel Working Party, and was agreed at a Kennel Club meeting attended by breed health co-ordinators from all affected breeds.

Two problems with the old system prompted the review. First, panellists found it difficult to distinguish reliably between Grade 0 (1% or less) and Grade 1 (just above 1%), as the boundary is a very fine subjective judgement. Second, breeders were concerned when dogs did not achieve Grade 0, even though there is no clinical difference in glaucoma risk between a Grade 0 and a Grade 1 dog under the old scheme.

The key clinical point is that dogs at genuine increased risk of developing glaucoma are those in Grade 3. Merging old grades 0 and 1 into a single new Grade 1 removes the most common source of examiner disagreement, loses no clinically meaningful information, and maintains a wider pool of dogs suitable for breeding — which helps preserve genetic diversity within affected breeds.

What this means for breeders

If your dog is examined from 2026 onwards, the best achievable result is Grade 1. This is a good result. A Grade 1 dog has 0 to 25% abnormality and is not at increased risk compared with a dog that previously graded 0.

If you have older certificates showing Grade 0, those remain valid historical records. A dog previously graded 0 under the old scheme would be expected to receive a Grade 1 under the current scheme, with no change to its actual clinical status.

Because PLA can progress with age in some breeds — most notably the Flat Coated Retriever and Golden Retriever — repeat gonioscopy every three years is recommended even for dogs with low-grade results. Both eyes are always examined, as PLA is bilateral but not necessarily symmetrical.

Which breeds need gonioscopy?

Gonioscopy is recommended for all breeds in which pectinate ligament abnormality is listed as an inherited condition under the BVA/KC/ISDS Eye Scheme. These currently include the Basset Hound, Border Collie, Dandie Dinmont Terrier, Hungarian Vizsla, Japanese Shiba Inu, Leonberger, Flat Coated Retriever, Golden Retriever, Siberian Husky, American Cocker Spaniel, Cocker Spaniel, English Springer Spaniel, Welsh Springer Spaniel, and the Spanish Water Dog.

For breeds in which a DNA test is also available, notably the Border Collie, gonioscopy and DNA testing are complementary rather than interchangeable. DNA testing identifies whether an individual carries the mutation; gonioscopy assesses the structural appearance of the drainage angle, which can vary even among mutation carriers.

Booking a gonioscopy appointment

Gonioscopy is performed before any dilating drops are used. When booking, please mention that your dog requires gonioscopy so that sufficient time can be allocated. For breeds that also require a routine eye examination, both tests are usually performed at the same appointment. The examination uses topical local anaesthetic drops only and is well tolerated by most dogs.