| Ectopia lentis | |
|---|---|
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| Ectopia lentis in a patient withMarfan syndrome.Zonular fibers are visible. | |
| Specialty | Medical genetics  |
Ectopia lentis is adisplacement or malposition of theeye'slens from its normal location. A partial dislocation of a lens is termedlens subluxation orsubluxated lens; a complete dislocation of a lens is termedlens luxation orluxated lens.
Although observed in humans and cats, ectopia lentis is most commonly seen indogs.Ciliary zonules 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 formation (decrease in lens diameter may stretch and break the zonules), orglaucoma (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 anterioruveitis (inflammation of the inside of the eye).[citation needed]
With anterior lens luxation, the lens pushes into theiris or actually enters theanterior chamber of the eye. This can cause glaucoma, uveitis, or damage to thecornea. Uveitis (inflammation of the eye) causes the pupil to constrict (miosis) and trap the lens in the anterior chamber, leading to an obstruction of outflow ofaqueous humour and subsequent increase in ocular pressure (glaucoma).[1] Better prognosis is valued in lens replacement surgery (retained vision and normal intraocular pressure) when it is performed before the onset ofsecondary glaucoma.[2] Glaucoma secondary to anterior lens luxation is less common in cats than dogs due to their naturally deeper anterior chamber and the liquification of thevitreous humour secondary to chronic inflammation.[3] Anterior lens luxation is considered to be an ophthalmological emergency.[citation needed]
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.[2]
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).[4] Other signs of lens subluxation include mildconjunctival redness, vitreous humour degeneration, prolapse of the vitreous into the anterior chamber, and an increase or decrease of anterior chamber depth.[5] Removal of the lens before it completely luxates into the anterior chamber may prevent secondary glaucoma.[2] 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.[6] A nonsurgical alternative treatment involves the use of a miotic to constrict the pupil and prevent the lens from luxating into the anterior chamber.[7]
Terrier breeds are predisposed to lens luxation, and it is probably inherited in theSealyham Terrier,Jack Russell Terrier,Wirehaired Fox Terrier,Rat Terrier,Teddy Roosevelt Terrier,Tibetan Terrier,[8]Miniature Bull Terrier,Shar Pei, andBorder Collie.[9] The mode of inheritance in the Tibetan Terrier[5] and Shar Pei[10] is likelyautosomal recessive.Labrador Retrievers andAustralian Cattle Dogs are also predisposed.[11]
In humans, a number of systemic conditions are associated with ectopia lentis:[12]
More common:
Less common: