Primary lens luxation in dogs: the ADAMTS17 DNA test, the terrier breeds and the go-now signs

Signs of Primary lens luxation

The 9 signs to watch for are listed below. Any one of them is a reason to consult your nearby vet; none of them is a diagnosis.

• Squinting or holding one eye shut
• A red eye that was normal yesterday
• A cloudy or blue-looking eye
• Tearing, or pawing and rubbing at the eye
• A pupil that looks odd, uneven or off-centre
• A visible shimmer or wobble in the eye
• An eye that looks large, firm or bulging
• A white spot visible in front of the iris
• Bumping into things after a sudden change

Breeds on this site that document this condition

Each breed page below carries the figure for this condition with its denominator and its source. The 10 breeds listed are the ones on this site that document it, not a ranking of risk.

What lens luxation in dogs is, and how often it turns up

Lens luxation in dogs is the lens falling out of position because the zonular ligaments that suspend it have weakened or broken. In the primary, inherited form those fibres were never normal, they degenerate over the dog's life, and the lens eventually breaks free and floats loose inside the eye. Partial breakdown gives a subluxation and complete breakdown gives a luxation.

The lens sits immediately behind the iris and does one job, which is focusing light onto the retina at the back of the eye. It is held there by a ring of fine fibres called zonules, and in a dog with primary lens luxation those zonules are abnormal from birth Cornell University College of Veterinary…. Nothing hurts and nothing shows until the day a lens moves, which is why this disease reaches the clinic as an emergency rather than as a gradual complaint.

Two figures give this a denominator, and both come from referral hospitals rather than from the general dog population. At the University of Zurich veterinary teaching hospital, 134 dogs with lens luxation were recorded between 2000 and 2011, which is 0.41 percent of all 32,523 dogs presented and 3.02 percent of every dog seen by the ophthalmology service in the same period. Of those 134 dogs, 86, or 64 percent, had primary lens luxation and 48, or 36 percent, had the secondary form; glaucoma caused 58 percent of the secondary cases, cataract 19 percent and trauma 17 percent.

The older British series settled what primary means. Curtis and colleagues classified 123 consecutive referred cases of lens dislocation as primary in 100 dogs, secondary in 21 and congenital in two, and found that every primary case was a terrier breed or a terrier crossbred, with a mean age of onset of four to five years and disease in both eyes. That paper also measured intraocular pressure daily for about a year in three Tibetan Terriers during the subluxation phase and found no abnormal pressure change, which is why the profession treats glaucoma here as a consequence of the moving lens rather than its cause.

One finding should change how an Indian reader reads every breed list on this page. When 27,254 dogs carrying an inherited disorder were compared against matched healthy controls across 24 conditions, lens luxation was one of 13 disorders that showed no difference in expression between purebred and mixed-breed dogs. The authors read that pattern as the signature of an ancient mutation already spread widely through the dog population, rather than a recent one concentrated in a few closed studbooks. India's dog population is overwhelmingly mixed, and a mixed-breed dog is not exempt.

How to read the OFA register without misreading it

The Orthopedic Foundation for Animals publishes the largest public count of who carries this mutation, and its table is worth reading properly. Read live on 24 September 2026, the register holds 17,677 primary lens luxation evaluations across 23 breeds, of which 70.3 percent were normal, 27.8 percent were carriers and 1.9 percent were at risk. Every one of the 24 rows in that table sums to between 99.9 and 100.1 percent, which is the arithmetic check this page ran before quoting any of them.

The rank column is the part people get wrong. OFA orders the breeds by the percentage testing abnormal, not by carrier frequency, so the Rat Terrier sits at rank 3 on 2.1 percent abnormal while four breeds carry the mutation more often than it does. Sorted by carrier frequency instead, the order runs Miniature Bull Terrier 47.9 percent, Jagd Terrier 43.6 percent, Sealyham Terrier 40.1 percent, Jack Russell Terrier 34.7 percent and then the Rat Terrier at 30.3 percent. These are dogs whose owners chose to test, so the register describes testing breeders, never the breed.

Which way the lens falls decides whether this is an emergency

To judge how urgent a luxated lens is, ask which way it fell. Anterior lens luxation, forward through the pupil into the chamber in front of the iris, blocks the eye's fluid drainage, drives the pressure up into acute glaucoma, and is treated as a medical emergency because it blinds eyes and hurts. Posterior luxation, backwards into the vitreous, causes milder inflammation and glaucoma is less likely.

The mechanism is plumbing. Aqueous fluid is made behind the iris and drains through the angle at the edge of the anterior chamber, so a lens sitting in that chamber acts as a plug, the fluid backs up, and the intraocular pressure rises. That pressure is what causes the pain and the blindness, not the displaced lens itself Orthopedic Foundation for Animals. VCA puts the contrast bluntly: a posteriorly luxated lens rarely causes discomfort, while an anterior luxation is extremely painful and can cause permanent blindness.

The price of arriving late has been measured. In a series of 60 dogs and 90 eyes presented late to a referral ophthalmology service, 45 eyes were luxated or subluxated, split as 25 anterior, 15 subluxated and 5 posterior; vision was lost in 18 of the 25 anterior luxations, 72 percent, in 5 of 15 subluxations, 33.3 percent, and in all 5 posterior luxations that had gone on to secondary glaucoma, 100 percent. The mean age of those dogs was 3.65 years with a standard deviation of 2.4 and a range of 1 to 12. Nearly three eyes in four were already blind by the time somebody acted.

The second eye is the part owners miss, and the literature is unusually specific about it. Primary lens luxation typically goes undetected until the lens displaces in one eye, and dogs typically present with the other lens already partially displaced, progressing to full displacement weeks to months later. Bilateral disease was significantly more common in the primary form than in the secondary form in the Zurich series, and the 1983 case series described essential bilaterality as one of the three defining features of the primary disease. Book the second eye before it moves, not after.

What an owner can actually see at home

Nine changes are worth acting on, and none of them needs equipment. A dog may squint or hold the eye shut, the white of the eye may redden, the eye may look cloudy or blue, it may tear, the dog may paw or rub at it, vision may fail suddenly, the pupil may look odd or uneven, there may be a visible shimmer or wobble in the eye as the loose lens moves, and the eye may look large, firm or bulging. The shimmer is the one worth learning, because a wobbling lens is a lens whose zonules have already begun to break.

Some dogs hide eye pain very well and go on eating and behaving normally while an eye hurts. That is why breed knowledge matters more here than observation: an owner of a Jack Russell Terrier, a Chinese Crested Dog or a Tibetan Terrier should treat any eye change as urgent by default, because these are the breeds in which the mutation actually segregates Gould D, Pettitt L, McLaughlin B, Holmes N.

How lens luxation in dogs is diagnosed

To diagnose lens luxation, a veterinarian examines the eye closely and measures the intraocular pressure, because the pressure reading is what separates a nuisance from an emergency Cornell University College of Veterinary…. The examination is also where the direction of the luxation is settled, and the direction decides the treatment. A diagnosis reached early is the single thing Cornell says is crucial here.

The instruments are ordinary and most Indian metro practices hold them. Tonometry, run with a hand-held instrument against the cornea, gives the intraocular pressure; a Schirmer tear test measures tear production; fluorescein stain shows up corneal scratches and ulcers; and a focused light lets the vet look into the eye Veterinary Partner. Where the view into the eye is blocked, an ocular ultrasound is used to evaluate the internal structures Voice of Stray Dogs (VOSD).

Referral to an eye specialist is often recommended, and it is recommended most strongly when the eye still has vision, because that is the eye worth operating on. Cornell states the position plainly: early detection is crucial, and a dog may be referred to a veterinary ophthalmology specialist for additional testing. Five steps make up the work-up.

1. Take the history first, including the breed, the age and how many hours or days the eye has looked wrong.
2. Measure the intraocular pressure in both eyes, since a raised pressure converts this into an emergency referral.
3. Stain the cornea to rule out an ulcer or a scratch as the cause of the pain.
4. Examine the inside of both eyes with a focused light, looking for a wobble, a subluxation or a lens sitting in front of the iris.
5. Ultrasound the eye when the view is blocked, then refer to an ophthalmologist if the eye is visual.

Primary or secondary, and why the answer changes what you do next

Separating primary from secondary lens luxation is not academic, because only one of them means the other eye is at risk and only one of them means the litter is at risk. Secondary luxation follows another eye disease, and the usual culprits are long-standing inflammation, glaucoma, cataract, an intraocular tumour or trauma VCA Animal Hospitals. In the Zurich series, secondary cases were significantly older, at a mean of 9.12 years with a standard deviation of 3.38, against 7.39 years with a standard deviation of 3.02 for the primary cases.

Breed predisposition is the strongest single clue a general practitioner has before any instrument comes out. The Zurich data showed primary lens luxation concentrated in terrier breeds, Chinese Crested dogs, Pinschers and Spitz types, while Siberian Huskies, Basset Hounds, Bearded Collies, Cairn Terriers, mixed-breed dogs, Boston Terriers, Borzois, Dobermanns, Leonbergers and Weimaraners turned up significantly more often with the secondary form. Sex made no difference to either. A DNA result on file settles the question before the eye ever moves, which is the argument for the next section.

The ADAMTS17 DNA test: one mutation, seventeen breeds, one answer

One mutation explains primary lens luxation in seventeen dog breeds, which makes this the rare inherited eye disease where a single DNA test answers the question for a whole group of breeds at once Online Mendelian Inheritance in Animals. The variant is ADAMTS17:c.1473+1, a single base change from G to A that destroys the splice donor recognition site in intron 10 of the ADAMTS17 gene on canine chromosome 3.

The mapping ran in two stages and both are published with their numbers. A genome scan using 364 microsatellites, run on 23 affected Miniature Bull Terriers with an equal number of obligate carriers and 23 affected Lancashire Heelers with an equal number of obligate carriers, narrowed the disease to a 6.3 megabase region in the middle of chromosome 3. A genome-wide association study on 28 affected and 20 control Jack Russell Terriers then hit the same region, and fine mapping brought it down to a 664 kilobase segment holding the positional candidate gene ADAMTS17 Online Mendelian Inheritance in Animals.

Then came the finding that makes this page's case. Gould and colleagues screened 121 dogs of 30 different breeds that were clinically affected with primary lens luxation, and found at least one dog homozygous for the same ADAMTS17 mutation in 14 breeds beyond the three it was first described in Online Mendelian Inheritance in Animals. The fourteen are the Australian Cattle Dog, Chinese Crested Dog, Jagdterrier, Parson Russell Terrier, Patterdale Terrier, Rat Terrier, Sealyham Terrier, Tenterfield Terrier, Tibetan Terrier, Toy Fox Terrier, Volpino Italiano, Welsh Terrier, Wire-haired Fox Terrier and Yorkshire Terrier. Add the original Miniature Bull Terrier, Lancashire Heeler and Jack Russell Terrier and the total is seventeen breeds, one variant, one test.

It is not the whole story, and the paper says so itself. Affected Shar Pei and Brittany Spaniels in that screen did not carry the variant, which means those two breeds suffer a genetically distinct form of the same disease. The Shar Pei's own version was later pinned to a different change in the same gene, a 6 base pair deletion in exon 22 of ADAMTS17, with a 4.24-fold drop in ADAMTS17 expression in affected ocular tissue. A clear result on the c.1473+1 test says nothing about a Shar Pei or a Brittany.

OFA runs that second Shar Pei variant as a separate test with its own register, and the register is small. Under the heading Shar-Pei primary open angle glaucoma and primary lens luxation, 78 Chinese Shar-Pei have been evaluated, of which 79.5 percent were normal and 20.5 percent were carriers, with no dog recorded as abnormal. Seventy-eight dogs is a thin denominator next to the 2,749 Miniature Bull Terriers on the main table, and it is the whole public record for that variant.

How much of the disease the test actually explains

The original study's own arithmetic is the honest answer, and it is published in two places. Of 196 dogs clinically diagnosed with primary lens luxation, 161 carried two copies of the variant, while 23 were heterozygous carriers and 12 had no copy at all, so 35 of the 196 clinically affected dogs did not have the affected genotype. UC Davis draws the right conclusion from it, that this variant is a common cause of the disease in several breeds but not the only one.

Two more numbers set the scale of the problem in the breeds that carry it. In the Miniature Bull Terrier, mutation frequency estimates ranged from 0.27 to 0.39, corresponding to 7.3 to 15.2 percent affected dogs in the breed. In a smaller, more recent survey, 82 Portuguese Podengos in the United Kingdom returned 1 dog homozygous for the mutation, 13 heterozygous and 68 clear, an allele frequency of 0.09 that the authors call high and use to argue for testing before every mating. The mutation also keeps turning up in breeds nobody had looked at: a panel screen of nearly 7,000 dogs across around 230 breeds for 93 variants found lens luxation risk among the variants appearing in breeds where it had not previously been documented.

The genetics arrived late enough to overturn what breeders had been told. A complex segregation analysis of 872 phenotyped Jack Russell Terriers, supported by pedigree data on a further 1,898 dogs, concluded in 2008 that cataracts and primary lens luxation were highly heritable, genetically correlated and not controlled by a single gene. Two years later a single causal variant was published. Both papers are correct about what they measured, and the lesson for a buyer is that a pedigree-based opinion ages badly next to a genotype.

The breed lists do not agree with one another, and that is a fact a buyer needs. UC Davis names 24 breeds and adds an open category of terrier breeds, the Royal Kennel Club validates only 10, an Australian specialist ophthalmology practice lists 17 accredited breeds, OMIA documents the phene in 25 breeds and the OFA register holds results for 23. The Royal Kennel Club is the only one that spells out the consequence, which is that the strength of the association between a mutation and disease risk can vary between breeds, and that a result in an unlisted breed should be interpreted with caution. Ask the laboratory which variant it runs and whether it is validated for your dog's breed.

Clear, carrier or affected: what each result means, and where the sources disagree

A PLL DNA test returns one of three results, and only two of them are simple. N/N means the dog carries no copy and will not develop this form and cannot pass it on; PLL/PLL means two copies, the dog will have or is at risk of the disease, and it passes the variant to every puppy. N/PLL means one copy, and that is where five authorities say five different things.

Start with the breeding arithmetic, because that part nobody disputes. A carrier transmits the variant to 50 percent of its offspring, and a mating between two carriers is predicted to produce 25 percent affected puppies. A carrier bred to a clear dog produces no affected puppies at all, which is the whole reason the test exists Animal Eye Care, Primary Lens Luxation….

The disputed part is whether a carrier can go blind itself. The primary paper is the one to weigh first: Gould and colleagues identified an increased risk of primary lens luxation associated with heterozygosity at ADAMTS17, and concluded that carriers carry a low risk of developing the disease. That is not a theoretical worry. In the original 196 clinically affected dogs, 23 were heterozygous carriers, not homozygotes.

Read the table as a spread rather than as a contradiction to be resolved. Five of the six sources put a carrier's own risk somewhere between 2 and 20 percent or decline to give a number, and one says the risk is zero Animal Eye Care, Primary Lens Luxation… University of California Davis School… The Royal Kennel Club. This page does not pick a winner, because the honest position for an owner is that a carrier is very unlikely to luxate and is not guaranteed not to. A carrier terrier with a red eye still gets the same-day appointment.

Recessive, codominant or additive, and why the label moves

The inheritance label moves between sources too, and it moves for a reason. OMIA records the mode of inheritance as autosomal recessive, as does UC Davis, Laboklin and the Royal Kennel Club LABOKLIN (UK), Primary Lens Luxation (PLL) The Royal Kennel Club. Cornell describes it as codominant or additive, meaning dogs with two copies are at the highest risk while dogs with one copy sit at an increased risk that is still far below theirs, and adds that the carrier's risk depends heavily on the breed. Both descriptions fit the same data; the second one is simply the more careful reading of a carrier risk that is small but not zero.

The practical consequence is a breeding rule rather than a cull. An Australian specialist practice makes the argument explicitly: in most of the affected breeds a large share of the population carries the variant, so removing every carrier and affected dog would damage the gene pool, and the workable answer is to know each dog's genotype and put carriers and affected dogs only to tested clear dogs. That produces carriers rather than affected puppies, and testing the next generation shrinks the allele frequency without shrinking the breed. The 47.9 percent carrier rate the OFA register records in the Miniature Bull Terrier is the reason that argument exists.

Treatment for lens luxation in dogs, in general terms

There is no cure for the inherited weakness itself, because the zonules of an affected dog are abnormal from birth and degenerate over time. Treatment is therefore about the lens that has moved and the pressure it has caused, and for an anterior luxation surgical removal of the displaced lens is the only effective treatment.

This page names no drug dose and never will, because dosing is a decision for the veterinarian looking at your dog. What is useful to know is the shape of the plan. The first goal is controlling pain, inflammation and eye pressure, using pressure-lowering eye medication, anti-inflammatory eye drops, pain medication and a drug to change the pupil size depending on where the lens sits, with emergency referral if the lens has moved forward. For a posterior luxation the usual approach is medication that keeps the pupil constricted so the lens cannot slip forward into the anterior chamber Voice of Stray Dogs (VOSD).

Two operations compete for the anterior case and both are published with outcome numbers. Intracapsular lens extraction removes the lens through an incision in the eye, closed with absorbable sutures. Trans-corneal reduction instead pushes the lens back behind the iris without opening the eye properly, which avoids a general anaesthetic procedure in a dog that cannot have one.

Read those four rows together and the picture is consistent rather than encouraging. Technical success is high, between 68 and 95 percent of eyes, while vision retention runs between 44 and 70 percent and is usually temporary Montgomery KW, Labelle AL. In the Palma series every visual eye eventually lost vision after trans-corneal reduction, glaucoma caused the loss in every case but one, and the authors now reserve the technique for dogs in which anaesthesia is contraindicated, where the owner has financial limits, or where the eye is already blind. A separate specialist practice puts the long-term success rate of surgically removing a loose lens at under 50 percent, rising to up to 75 percent when a small-incision technique is used before the zonules break completely.

That last figure is the strongest argument on this page for testing a dog before its eye ever moves. If surgery done early on a wobbling lens does better than surgery done on a lens already in the anterior chamber, then knowing a dog is homozygous at three years old buys the better operation. The same practice recommends that homozygous affected dogs be examined by a veterinary ophthalmologist every six months from twelve months of age to monitor lens stability.

When the answer is to remove the eye

Removing a blind, painful eye is a treatment, not a failure. If surgical removal of the lens is not possible, enucleation can be performed to relieve the pain of the condition, and where the eye is blind and painful that is often the kindest option, with most pets doing very well and feeling much better once the painful eye is gone. Enucleation can be done by a general veterinarian rather than by a specialist, which matters in an Indian city with no ophthalmology referral service.

Complications are published honestly by the same sources that recommend the surgery. Persistent glaucoma is one of the commonest complications of anterior lens luxation and can be difficult to treat, and retinal detachment is the other, after which the eye usually stays blind although it is generally pain-free. Post-operative inflammation was significantly more common after intracapsular lens extraction than after trans-corneal reduction. Recovery in the Indian practice described by VOSD means a strict two-week rest period, leash walking only, a recovery cone and lifelong medication where inflammation, glaucoma or retinal detachment follow.

Lens luxation in India: no laboratory, no published series, and what it costs

India has no published canine lens luxation record and no laboratory selling the ADAMTS17 test, and both of those are checked absences rather than assumptions. A PubMed search for canine lens luxation scoped to India returned zero records on the title and abstract search and zero on the author affiliation search, while the controls passed in the same session.

Both instruments were run on 24 September 2026, because they find different papers. Searching lens luxation with dog, dogs or canine in the title and abstract field, plus India in the title and abstract field, returned 0 records, and the identical search with India in the author affiliation field also returned 0. Two controls rule out a broken search. Dropping only the India term returned 52 canine lens luxation records, and a control for Indian veterinary ophthalmology, searching dog or canine in the title and abstract with India in the author affiliation field, returned 10 records, among them Indian work on canine ocular thelaziosis and the only published Indian canine progressive retinal atrophy series. Indian veterinary ophthalmology publishes. It has simply never published on this disease.

The contrast with the human literature is worth a sentence, because it shows the capacity exists. The same database returns 67 records for lens luxation or ectopia lentis with an Indian author affiliation, all of them human ophthalmology, including a clinical profile of ectopia lentis in a large cohort of children from an Indian tertiary eye care network and a survey of how Indian paediatric ophthalmologists manage cataract and ectopia lentis. India has the eye surgeons and the case volume. Nobody has counted the dogs.

The testing gap is just as concrete. Two Indian-facing laboratories sell dog DNA panels, and neither names this disease. The DNA Labs India dog DNA test page, priced at Rs 16,000 with free home collection in 300 or more cities and results in 10 days, names drug sensitivities, progressive retinal atrophy and hip dysplasia as its example conditions and never uses the words lens luxation. The EasyDNA India animal testing index does not contain the word lens, the word retinal or even the word eye. Neither page was searched by eye alone; both were fetched and searched as saved text.

Every rupee figure above was divided by 84.38 and by 74 before publication, and none of them lands on a round dollar amount, so none is a converted foreign price. Rs 2,500 is USD 29.63 at 84.38 and USD 33.78 at 74; Rs 3,000 is USD 35.55 and USD 40.54; Rs 15,000 is USD 177.77 and USD 202.70 Supertails, How Much Does a Corgi Cost…. Two honest caveats belong with the private figure. It prices cataract surgery, not lens luxation surgery, and it is published by a retailer with no denominator and no source attached; the page prints it with the rupee sign, as ₹3,000 to ₹6,000 for diagnostics and ₹15,000 to ₹30,000 for surgery. Treat it as the nearest published Indian number for intraocular eye surgery and not as a quotation for this operation.

Geography limits every Indian figure on this page, and the limit is worth stating rather than hiding. The only Indian veterinary fee table this page could open is the Madras Veterinary College one in Chennai, Tamil Nadu. No equivalent published government rate card was found for Mumbai or elsewhere in Maharashtra, for Delhi, for Bengaluru or elsewhere in Karnataka, for Hyderabad, for Pune or for Kolkata, so an owner in any of those cities is reading a Chennai price and should ask their own hospital for its own table. There is a second reason to say so out loud. The page that ranks first in India for this condition is published by an organisation whose corporate office is on HAL Airport Road in Bangalore and which describes itself as running India's largest referral hospital for dogs, and even that page prints no Indian price.

The sample-shipping route, step by step

The route out of India is a postal one and it is not complicated. All three overseas laboratories work from a cheek brush rather than blood, all three post a kit, and OFA states plainly that owners can collect the sample at home, that the process is non-invasive and that no veterinary appointment is necessary University of California Davis School… Genomia, Testing of dogs: PLL. Turnaround is at least 15 business days at UC Davis, 1 to 3 weeks from receipt at the Royal Kennel Club and 12 business days at Genomia, and every one of those clocks starts when the sample lands, not when it is posted Genomia, Testing of dogs: PLL.

One detail costs Indian buyers money and nobody warns them about it. The Royal Kennel Club kit ships with a pre-paid return envelope, which is pre-paid for a United Kingdom posting, so an Indian owner pays international courier charges on the return leg that a British owner does not. UC Davis simply asks that the brushes be placed in an envelope and returned to the address provided, with no pre-paid leg at all. Neither page publishes an India shipping charge, so this page does not print one; ask the courier before you buy the test.

The clinical side is better provided for than the genetic side. The Madras Veterinary College Teaching Hospital in Chennai, run by Tamil Nadu Veterinary and Animal Sciences University, lists Ophthalmology as a named referral unit of Surgery, alongside soft tissue surgery, orthopaedics and radiology, and handles more than one lakh cases a year. Its pharmacy runs on an average annual budget of Rs 25,00,000 and dispenses drugs and fluids free of cost to animals brought to the hospital, which matters for a disease whose first hours are about pressure control. It opens 8 am to 1 pm on weekdays and 8 am to 11.30 am on Saturdays, Sundays and government holidays, so an eye that goes wrong on a Sunday evening needs a private clinic.

The page that ranks first in India for this condition is worth naming, because it shows the size of the hole. Measured on 24 September 2026, the top Indian result runs 803 words and contains no percentage, no study denominator, no rupee figure and not one use of the word India. Four of the other ranking pages contain no number at all VCA Animal Hospitals Cornell University College of Veterinary… Orthopedic Foundation for Animals.

What to ask before you buy a terrier puppy in India

To avoid buying a dog that will luxate, ask for the ADAMTS17 DNA result on both parents before you pay, by name and on paper. Two clear parents cannot produce an affected puppy, and one clear parent cannot produce one either, which is why the genotype of the pair is the only question that settles it.

Kennel club rules make the certificate worth less than the laboratory report unless you check one thing. The Royal Kennel Club records a DNA result on a dog's profile only when the test comes from a laboratory on its own approved list and only when the test is recognised for that specific breed, and results from laboratories not on the list are not recorded at all The Royal Kennel Club. India has no equivalent national recording scheme, so an Indian buyer is reading a private laboratory report rather than a registry entry. Six questions cover it.

1. Ask for the ADAMTS17 result on the sire and the dam, named as N/N, N/PLL or PLL/PLL.
2. Ask which laboratory ran it, since a kennel club records a result only from a laboratory on its own approved list.
3. Ask whether that test is validated for this breed, because a result in an unlisted breed carries an uncertain association with disease.
4. Ask to see the report itself, not a line in an advertisement, with the dogs' registered names on it.
5. Ask whether any relative has luxated a lens, since the disease runs in families and the primary form is essentially bilateral.
6. Ask about the eyes as well as the genes, because a breed can carry more than one inherited eye disease at once.

That last question is not padding, and one breed proves it. A genetic analysis of 849 Tibetan Terriers from 596 litters in 203 kennels, examined under a standardised German scheme between 1987 and 2001, estimated the heritability of primary lens luxation in the breed at 0.13 with a standard error of 0.04, alongside separate heritabilities for persistent pupillary membrane at 0.17, non-congenital cataract at 0.13 and progressive retinal atrophy at 0.49. A Tibetan Terrier clear for ADAMTS17 has been cleared of one of four documented inherited eye problems in its breed. Our page on progressive retinal atrophy in dogs covers the one with the highest heritability of the four.

What the test cannot do, said plainly

A clear ADAMTS17 result clears a dog of one variant, not of lens luxation. Thirty-five of the 196 dogs in the founding study were clinically affected without two copies of the variant, affected Shar Pei and Brittany Spaniels carry a different genetic form entirely, and secondary lens luxation follows cataract, glaucoma, uveitis, trauma or an intraocular tumour in a dog with perfectly normal genes Betschart, Haessig. In the Zurich series, 48 of 134 luxations were secondary, and glaucoma alone accounted for 58 percent of those.

For an Indian buyer the harder problem is the paperwork rather than the biology. Our guide to dog breeder checks in India sets out what to ask for in writing before you pay, and KCI registration explained covers what a Kennel Club of India certificate does and does not say about health testing. Neither a pedigree nor a registration number is a health test.

One more piece of advice belongs here because it is counter-intuitive. Do not ask a breeder to promise that no dog in the line carries the variant, because in several of these breeds most of the breeding population does. The OFA register puts carriers at 47.9 percent of 2,749 tested Miniature Bull Terriers and 34.7 percent of 1,972 tested Jack Russell Terriers, and a specialist practice warns that excluding every carrier would damage the gene pool. A breeder who tests, publishes and mates carriers only to clear dogs is doing the right thing; a breeder who says the line is clean without a report is not.

Living with a dog that has had a lens removed or an eye removed

A dog usually lives well after this disease is treated, even when an eye is lost. Most pets do very well after eye removal and feel much better once the painful eye is gone, and dogs that keep a lens-free eye still see, although they become long-sighted without the lens and their vision is never perfect again VCA Animal Hospitals.

The recovery is short and strict. A dog may be hospitalised for a few days after surgery for monitoring, and once home it must be kept quiet, with no jumping and no running up or down stairs, and short leash walks as the only exercise for the first few weeks. The Indian account of the same protocol adds a two-week rest period, a recovery cone to stop the dog pawing at the face, and a crate where restricting activity is otherwise impossible. All post-operative medication is given exactly as the surgeon directs, and a problem of any kind means calling the clinic rather than waiting.

The remaining eye is the thing to watch for the rest of the dog's life. Long-term care means regular eye pressure checks, long-term eye drops where they are needed, and monitoring the other eye, especially in a breed at risk. Where one eye has had primary lens luxation the other may also be at risk, and a veterinarian or eye specialist may recommend preventive medication or regular examinations for it. Some ophthalmologists prefer to operate on a subluxated second lens before it dislocates completely, to avoid the complications that come with a complete luxation.

Prognosis is honest in the sources and it turns on time. The outlook depends on where the lens is, how long it has been out of place, whether glaucoma is present and whether the eye can still see, and if treated quickly some pets keep useful vision, while if pressure stays high too long vision is lost. Even where vision cannot be saved, treatment usually keeps the dog comfortable. The Indian reading of that is simple: the difference between a seeing dog and a blind one is measured in hours, and in most Indian cities those hours are spent finding a clinic.

• Keep the furniture where it is, because a dog with reduced vision navigates a familiar room from memory.
• Keep food and water bowls in one fixed place, every day.
• Gate the stairs during the strict rest period after surgery.
• Use a leash rather than a free run in any unfamiliar place while the dog adjusts.
• Book the pressure checks in advance, since the remaining eye needs them for life.
• Treat any new squint, redness or cloudiness as urgent, in either eye.