Verwijscase SDU: Lens Luxation

Summary

This ocular problem may affect dogs and cats and may develop acutely or have a more chronic presentation depending on a variety of factors, some of which are mentioned below (i.e. see ‘points to remember’). All patients suspected to have lens luxation should be referred. It is important to provide a thorough history that focuses on the presence of vision prior to lens luxation and also the results of general a physical exam, as some of these patients will undergo surgery. Early referral is pivotal to determine the next steps for each patient, including whether lens removal surgery might be recommended. The work up at the ophthalmologist will include a thorough eye exam with particular attention to bilateral intraocular pressure measurement, funduscopy if possible, and the presence of possible subluxation in the eye that appears to be unaffected. Sometimes a DNA test for Primary Lens Luxation (PLL) might be carried out. In some patients, an ocular ultrasound and even an ERG (i.e. an electroretinogram, a test that is often performed under general anesthesia) might be recommended.

The following points to remember are based on articles / texts, and personal clinical experience: 

Possible presentations of lens luxation of lens luxation:

• Anterior luxation (the lens moves into the anterior chamber)
• Posterior luxation (the lens falls into the vitreous IF the vitreous is liquified /degenerated)
• Subluxation (the lens is moving but it is not completely loose). This might make the lens and the iris ‘wobble’ during ocular movement. We call the wobble ‘iridodonesis’ and ‘phacodonesis’. There may be a deep anterior chamber and/or presentation of the vitreous humor into the anterior chamber.

Eye pressure (IOP) possibilities (references vary, but a healthy range is about 12-24 mmHg): 

• High eye pressure (i.e. secondary glaucoma – due to luxation / subluxation) 
• Normal eye pressure (i.e. normotensive luxation / subluxation) 

An acute increase in IOP is found:  

• IF there is vitreous in the anterior chamber, even if the lens is not in the anterior chamber
• IF there is anterior luxation AND the lens blocks aqueous humor from travelling normally between the small space behind the iris (i.e. the posterior chamber) and the anterior chamber. This is called ‘pupil block glaucoma’ and it is always an eye emergency. 

A normal IOP is seen sometimes: 

• Veterinarians often do not know that lens luxation can be normotensive in some cases.
• If there is anterior lens luxation BUT there is enough space in the anterior chamber for the lens (i.e. in some dogs from breeds like border collies and cavaliers, and in cats (Fig 5.))

Primary Lens Luxation (PLL):

• There are different forms of lens luxation. There is a hereditary form of lens luxation (i.e. ‘primary’ lens luxation or PLL). There are also secondary forms (i.e. secondary to uveitis in cats, and secondary to glaucoma with globe enlargement in dogs, for instance). 
• The defective gene locus of PLL is found in the ADAMTS17 gene and was found in 2010
• PLL has been shown to ocur in a variety of breeds including most terriers as well as Lancanshire Heelers, Australian cattle dog, Chinese crested dog, Volpino Italiano and the Tibetan terrier (although this is not a true terrier). Shar Peis and Brittany spaniels also get lens luxation, but it is not caused by the same gene defect as in these other breeds, so it is clear there is more than one gene (i.e. genotype) that can be affected and cause lens luxation (i.e. the clinical phenotype we see in this disease).
• There is a gene test for PLL for those listed breeds. Homozygotes for the mutation (i.e. animals with two copies of the mutation) will have the disease (i.e. 10% are expected to be affected by 3 years of age and 100% are expected to be affected by 6 years of age). Interestingly, heterozygotes (i.e. one normal copy and one affected copy) are not just ‘carriers’ as 5% may be affected by age 3 and up to 60% may be affected by age 10. 

Treatment possibilities include medical and surgical options. It is important to note that both possibilities will need medication and re-examinations for life, and that the risks between the options differ: 

• Medical options: focuses on keeping the pupil small (use of latanoprost 2x day minimally, plus oral and/or topical anti-inflammatory depending on case) so that the lens does not move into the anterior chamber. ONLY possible IF the lens is completely behind the iris. If the lens is in the anterior chamber ‘transcorneal reduction’ (i.e. pushing the lens back, so it goes behind the iris, by acutely applying pressure on the cornea) might be of help for some patients that do not have adhesions between the iris and lens. However, this is traumatizing for the eye and requires a general anesthesia or a deep sedation and local anesthetic, and it should only be attempted by an ophthalmologist. Upside: surgery is avoided at that moment. Downside: there is a loose lens that causes micro-trauma inside of the eye, and the lens will develop a cataract over time and lens-induced uveitis. Also, surgery might still be needed if the lens luxates anteriorly again. It is worth remembering that if the lens becomes adhered to the retina the ‘window’ for surgery is lost.
• Surgical options: focuses on removal of the lens and restoring / maintaining IOP. It is better to operate early, before a high pressure develops. Some eye drops will still be necessary for the long term. Upside: recurring lens luxation, lens-induced uveitis or microtrauma are no longer possible. Downside: surgery is needed. 

Lens extraction surgery (general comments and prognosis): 

• Good (to fair) prognosis with a low IOP, OR with a moderate-high IOP and surgery in ≤24 h
• Surgical technique may involve a (large) 180-degree corneal incision, OR a small incision (i.e. a similar technique to cataract surgery)
• At the SDU 80% of patients can have small incisional surgery for luxated lens removal, but early referral is essential to avoid corneal edema (i.e. the surgeon cannot see through an edematous cornea and needs to perform a 180-degree corneal incision in those cases).
• Animals can adapt to vision without a lens. Unfortunately, a lens implant (i.e. an intraocular lens or IOL) cannot be used in lens luxation cases. This is because an IOL is fitted inside a lens capsule and the entire lens, including the lens capsule, is removed in lens luxation cases so there is nowhere for the IOL to go. 

Further reading (you may enter the title of the articles in www.pubmed.com to read the abstract): 

Farias FHG et al. An ADAMTS17 Splice Donor Site Mutation in Dogs with Primary Lens Luxation.
Investigative Ophthalmology and Visual Science. 2010; 51(9): 4716-4721.

Gould D et al (2011) ADAMTS17 mutation associated with primary lens luxation is widespread among breeds. Veterinary Ophthalmology. 2011; 14(6): 378-384.  

Gharahkhani P, O’Leary C, Duffy D, Bernays M, Kyaw-Tanner M. Primary Lens Luxation in Australian Tenterfield and Miniature Bull Terriers is Due to An Old ADAMTS17 Mutation and is an Additive Trait. The Open Genomics Journal. 2012; 5: 7-13. 

Glover TL, Davidson MG, Nasisse MP, Olivero DK. The intracapsular extraction of displaced lenses in dogs. a retrospective study of 57 cases (1984 –1990). Journal of the American Animal Hospital Association. 1995; 31: 77–81. 

Montgomery KW, Labelle AL, Gemensky-Metzler AJ. Trans-corneal reduction of anterior lens luxation in dogs with lens instability: a retrospective study of 19 dogs (2010-2013). Veterinary Ophthalmology. 2014; 17(4): 275-259.  

Binder DR, Herring IP, Gerhard T. Outcomes of nonsurgical management and efficacy of demecarium bromide treatment for primary lens instability in dogs: 34 cases (1990-2004). Journal of the American Veterinary Medical Association. 2007; 231(1): 89-93.  

Michau TM. Surgery of the lens (Ch. 23). In: Veterinary Ophthalmology. Gelatt KN, Ben-Shlomo G, Gilger BC, Hendrix DVH, Kern TJ and Plummer CE editors. 6Th Edition. Wiley-Blackwell. 2021: Pg: 1371. 

Specialist

Rick F. Sanchez, BSciBiol, DVM, CertVOphthal, DipECVO, CertVetEd / FHEA 
EBVS accredited, European Specialist in Veterinary Ophthalmology 

Patiënt

• Fox (dog1): Jack Russel Terrier, Male, 5 years old – Presented with sudden onset pain right eye (OD).
• Madam (dog2): Tibetan terrier, Female neutered, 6 years old – Sudden onset pain right eye (OD).
• Baby (doge): Jack Russell Terrier, Female/spayed, 8 years and 8 months old – Bilateral lens luxation. 
• Lady (cat): Domestic short hair, Female spayed, 12 years old – Sudden development of ‘strange’ eyes (OU).
• Franky (dog4): Mixed breed, Male neutered, 8 years old – Sudden onset pain right eye (OD). 

Medical imaging

Figure 1A-C. Shows the right eye (OD) of Fox, a Jack Russell Terrier, male / castrated, 5 years of age that presented with sudden onset pain right eye. The ‘glassy’ edge of the lens is seen in the anterior chamber, which also has central corneal edema (Fig. 1A). The patient presented with ocular pain (Fig 1B) and conjunctival as well as episcleral hyperemia (Fib 1C), and a high intraocular pressure (45mmHg).  

Figure 2. Shows the early post-operative appearance of a right eye (OD) of a Tibetan terrier, male/ castrated, 6 years of age, that presented with a hypertensive anterior luxation. The patient has undergone a 180-degree corneal incision. The eye was comfortable and seeing well and was on prophylactic medical therapy for life (i.e. in this case a dexamethasone drop and a carbonic anhydrase inhibitor drop). The incision line consisted of simple interrupted microsutures and a superimposed continuous microsuture. Edema around the corneal incision is common for some weeks until the wound heals and the suture dissolves. A large incision will invariably affect corneal innervation in part of the cornea and cause more tissue trauma than smaller incisions.  

Figure 3. Image of a patient’s eye that underwent lens luxation surgery using a small incision technique, as that used for standard cataract surgery, instead of a 180-degree corneal incision. The very small incisions (i.e. one of 2.8mm and one of 1mm per eye) cause very little corneal damage. The patient was on long term, prophylactic use of a low dose of a topical steroid (dexamethasone) drops as well as twice daily applications of brinzolamide for life, and he was followed up with eye examinations twice yearly. The image shown is form almost 2 years after surgery. She is visual, active, and very happy.  

Figure 4. Example of a cat (domestic short hair, female spayed, 12 years of age) with a history of chronic, bilateral, low-grade uveitis and secondary anterior lens luxation bilaterally with normotension. The lenses are in the anterior chambers in both eyes, but the eyes look different. This is because the lens in the right eye (OD) has a cataract and this makes the anterior chamber look white, while the lens in the left eye (OS) has no cataract and we can see the tapetal reflex (i.e. the yellow glow) through the cornea and lens. She underwent bilateral lens extraction surgery with small incisional phacoemulsification followed by medical supportive treatment. Contact of the lens with the corneal endothelium in cats will often lead to corneal vascularization. Corneal edema in cats due to contact of the endothelium with the lens is uncommon.  

Figure 5A-C. Right eye (OD) of a patient (mixed breed, male neutered, 8 years of age) that presented with anterior luxation (A). The lens was trapped in the anterior chamber because the referring veterinarian had treated the eye with a miotic (i.e. a drop to reduce the size of the pupil and also reduce pressure), while there was anterior luxation. The pupil did not become small because the lens was blocking it from getting smaller, but this also kept the lens in the anterior chamber and caused pupil block glaucoma. Unfortunately, this caused patient discomfort, acute eye pressure increase and corneal edema due to lens contact with the corneal endothelium. The patient was a good candidate for surgery, but the owner could not afford anesthesia or surgery, and ‘transcorneal reduction’ was also out of the question cost-wise. The patient was treated with atropine in the hospital and under constant supervision (help on a lap with the nose pointing up) until the pupil dilated, which took 45 minutes, then, the eye was gently massaged and, luckily, the lens dropped on its own into the posterior segment behind the iris as there were no synechiae between the iris and lens (B). The lens had nuclear sclerosis, which is obvious in the second image although it was not obvious in the first. The eye was then treated with latanoprost (i.e. a pressure reducing eye drops that is also a potent miotic) until the pupil was closed (C). In this image, the central cornea still has edema due to recent lens contact with the endothelium. The patient was sent home on an course of an oral NSAID, and long term use of a low dose of a topical steroid (dexamethasone) drops as well as twice daily applications of latanoprost for life, and he was followed up with eye examinations twice yearly and has done well. The long-term risk for this patient is lens-induced microtrauma, lens induced-uveitis and the possibility of recurrence of anterior lens luxation. 

Further information

In addition to the information already presented /discussed in this article one can add that there is a surprisingly small amount of information regarding the long-term prognosis of surgical and medical treatment options, especially when it comes to studies that, due to study design, would offer the most reliable evidence (i.e. prospective, randomized, controlled, ‘masked’ clinical studies) as some of the aspects of the study design would be difficult to impossible to implement.  

Most of the available literature on surgery dates to the 80s or 90s and this is old enough to warrant new studies with newer techniques that have become available since. Another problem is that most studies (i.e. on surgical and medical options) do not extend long enough to include a significant follow up to draw conclusions from (i.e. not just up to 1 year, but much more and ideally up to 4-5 years). This means that different ophthalmologists often have different personal biases when it comes to treating these patients medically or surgically.  

Generally speaking, the prognosis of cases that are operated early that do not have glaucoma on presentation or that have had a high pressure for no longer than 24 hours tend to do well, especially with small incisional surgery. We know that cases managed medically can do well for at least a year, sometimes more, but we do not know what problems they might develop in 4 or 5 years, and this is important because many animals are affected at ages of 3-7 years in breeds that might live up to 10 or 14 years. Cases with a posteriorly luxated lens (i.e. a lens that is in the vitreous) are often accompanied by vitreous degeneration (i.e. liquefaction of the vitreous) and this means the lens can move freely in the back of the eye causing microtrauma as it knocks around inside the large space available behind the pupil.

Also, when a lens is not in its intended anatomical position, sooner or later it will develop a cataract, and this will lead to lens-induced uveitis. The lens can become adhered to the retina, and this can lead to further issues through tissue inflammation, accumulation of inflammatory cells in certain parts of the eye, other microscopic changes and even the development of internal neovascularization.

These potential risks need to be considered in all animals and especially in animals that are young adults, as years of lens-induced uveitis, even when medically managed, could lead to secondary glaucoma and the loss of the eye.

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