Ectopia lentis is a displacement or malposition of the

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

crystalline lens The lens, or crystalline lens, is a transparent biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. By changing shape, it functions to change the focal length of the eye so that it ca ...

from its normal location. A partial dislocation of a lens is termed lens subluxation or subluxated lens; a complete dislocation of a lens is termed lens luxation or luxated lens.

Ectopia lentis in dogs and cats

Although observed in humans and cats, ectopia lentis is most commonly seen in dogs.

Ciliary zonules The zonule of Zinn () (Zinn's membrane, ciliary zonule) (after Johann Gottfried Zinn) is a ring of fibrous strands forming a zonule (little band) that connects the ciliary body with the crystalline lens of the eye. These fibers are sometimes co ...

normally hold the lens in place. Abnormal development of these zonules can lead to primary ectopia lentis, usually a bilateral condition. Luxation can also be a secondary condition, caused by trauma,

cataract A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble w ...

formation (decrease in lens diameter may stretch and break the zonules), or

glaucoma Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye re ...

(enlargement of the globe stretches the zonules). Steroid administration weakens the zonules and can lead to luxation, as well. Lens luxation in cats can occur secondary to anterior

uveitis Uveitis () is inflammation of the uvea, the pigmented layer of the eye between the inner retina and the outer fibrous layer composed of the sclera and cornea. The uvea consists of the middle layer of pigmented vascular structures of the eye an ...

(inflammation of the inside of the eye).

Anterior lens luxation

With anterior lens luxation, the lens pushes into the iris or actually enters the anterior chamber of the eye. This can cause glaucoma, uveitis, or damage to the

cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical ...

. Uveitis (inflammation of the eye) causes the pupil to constrict (

miosis Miosis, or myosis (), is excessive constriction of the pupil.Farlex medical dictionary
citing: ...

) and trap the lens in the anterior chamber, leading to an obstruction of outflow of

aqueous humour The aqueous humour is a transparent water-like fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary body, a structure supporting the lens of the eyeball. It fills both the anterior and the posteri ...

and subsequent increase in ocular pressure (glaucoma). Better prognosis is valued in lens replacement surgery (retained vision and normal intraocular pressure) when it is performed before the onset of secondary glaucoma. Glaucoma secondary to anterior lens luxation is less common in cats than dogs due to their naturally deeper anterior chamber and the liquification of the

vitreous humour The vitreous body (''vitreous'' meaning "glass-like"; , ) is the clear gel that fills the space between the lens and the retina of the eyeball (the vitreous chamber) in humans and other vertebrates. It is often referred to as the vitreous humo ...

secondary to chronic inflammation. Anterior lens luxation is considered to be an ophthalmological emergency.

Posterior lens luxation

With posterior lens luxation, the lens falls back into the vitreous humour and lies on the floor of the eye. This type causes fewer problems than anterior lens luxation, although glaucoma or ocular inflammation may occur. Surgery is used to treat dogs with significant symptoms. Removal of the lens before it moves to the anterior chamber may prevent secondary glaucoma.

Lens subluxation

Lens subluxation is also seen in dogs and is characterized by a partial displacement of the lens. It can be recognized by trembling of the iris ( iridodonesis) or lens ( phacodonesis) and the presence of an aphakic crescent (an area of the pupil where the lens is absent). Other signs of lens subluxation include mild

conjunctiva The conjunctiva is a thin mucous membrane that lines the inside of the eyelids and covers the sclera (the white of the eye). It is composed of non-keratinized, stratified squamous epithelium with goblet cells, stratified columnar epitheli ...

l redness, vitreous humour degeneration, prolapse of the vitreous into the anterior chamber, and an increase or decrease of anterior chamber depth. Removal of the lens before it completely luxates into the anterior chamber may prevent secondary glaucoma. Extreme degree of luxation of lens is called "lenticele" in which lens comes out of the eyeball and becomes trapped under the Tenon's capsule or conjunctiva. A nonsurgical alternative treatment involves the use of a miotic to constrict the pupil and prevent the lens from luxating into the anterior chamber.

Breed predisposition

Terrier breeds are predisposed to lens luxation, and it is probably inherited in the

Sealyham Terrier The Sealyham Terrier ( cy, Daeargi Sealyham) is a rare Welsh breed of small to medium-sized terrier that originated in Wales as a working dog. It is principally a white-bodied, rough-coated breed, developed in the mid-to-late-19th century by C ...

Jack Russell Terrier The Jack Russell Terrier is a small terrier that has its origins in fox hunting in England. It is principally white-bodied and smooth, rough or broken-coated and can be any colour. Small tan and white terriers that technically belong to oth ...

, Wirehaired Fox Terrier, Rat Terrier, Teddy Roosevelt Terrier,

Tibetan Terrier The Tibetan Terrier is a medium-sized breed of dog that originated in Tibet.American Kennel Club (2013). '' Get to know the Tibetan Terrier.'' Retrieved from http://www.akc.org/breeds/tibetan_terrier/index.cfm Despite its name, it is not a membe ...

, Miniature Bull Terrier, Shar Pei, and Border Collie. The mode of inheritance in the Tibetan Terrier and Shar Pei is likely

autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and ...

. Labrador Retrievers and Australian Cattle Dogs are also predisposed.

Systemic associations in humans

In humans, a number of systemic conditions are associated with ectopia lentis:Eifrig CW, Eifrig DE
"Ectopia Lentis"
eMedicine.com. November 24, 2004. More common: *

Marfan syndrome Marfan syndrome (MFS) is a multi-systemic genetic disorder that affects the connective tissue. Those with the condition tend to be tall and thin, with long arms, legs, fingers, and toes. They also typically have exceptionally flexible joints a ...

(upward and outward) * Homocystinuria (downward and inwards) * Weill–Marchesani syndrome *

Sulfite oxidase deficiency Sulfite oxidase () is an enzyme in the mitochondria of all eukaryotes, with exception of the yeasts. It oxidizes sulfite to sulfate and, via cytochrome c, transfers the electrons produced to the electron transport chain, allowing generation of A ...

* Molybdenum cofactor deficiency * Hyperlysinemia Less common: * Ehlers–Danlos syndrome *

Crouzon disease Crouzon syndrome is an autosomal dominant genetic disorder known as a branchial arch syndrome. Specifically, this syndrome affects the first branchial (or pharyngeal) arch, which is the precursor of the maxilla and mandible. Since the branchial ...

Refsum syndrome Refsum disease is an autosomal recessive neurological disease that results in the over-accumulation of phytanic acid in cells and tissues. It is one of several disorders named after Norwegian neurologist Sigvald Bernhard Refsum (1907–1991). Ref ...

Kniest syndrome Kniest dysplasia is a rare form of dwarfism caused by a mutation in the ''COL2A1'' gene on chromosome 12. The ''COL2A1'' gene is responsible for producing type II collagen. The mutation of ''COL2A1'' gene leads to abnormal skeletal growth and pr ...

* Mandibulofacial dysostosis *

Sturge–Weber syndrome Sturge–Weber syndrome, sometimes referred to as encephalotrigeminal angiomatosis, is a rare congenital neurological and skin disorder. It is one of the phakomatoses and is often associated with port-wine stains of the face, glaucoma, seizures, ...

* Conradi syndrome *

Pfaundler syndrome Hurler syndrome, also known as mucopolysaccharidosis Type IH (MPS-IH), Hurler's disease, and formerly gargoylism, is a genetic disorder that results in the buildup of large sugar molecules called glycosaminoglycans (GAGs) in lysosomes. The inab ...

* Pierre Robin syndrome * Wildervanck syndrome * Sprengel deformity

References

External links

GeneReviews/NCBI/NIH/UW entry on ADAMTSL4-Related Eye Disorders, Autosomal Recessive Isolated Ectopia Lentis, Ectopia Lentis et Pupillae
{{Congenital malformations and deformations of eye, ear, face and neck Dog diseases Cat diseases Congenital disorders of eyes Disorders of lens