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what are the causes of ectopic and dislocated lenses, and what are the causes of ectopic and dislocated lenses

what are the causes of ectopic and dislocated lenses, and what are the causes of ectopic and dislocated lenses

Etiology of ectopic and dislocated lens

I. Etiology

Abnormal crystal position can be caused by congenital development abnormality. If the crystal is not in normal position after birth, it can be called crystal ectopic; If the lens position changes due to congenital factors, trauma or pathological changes after birth, it can be collectively referred to as lens dislocation or lens subluxation. However, in the case of congenital abnormal crystal position, it is sometimes difficult to distinguish when the crystal position changes, so there is no strict boundary between crystal dislocation or ectopic, which is often common.

1. Congenital ectopic or dislocated lens

It can be regarded as a single congenital anomaly; Or with pupil ectopic and other ocular abnormalities; Or complicated with systemic syndrome with abnormal development of mesoderm, especially bone. In any case, due to the weak suspensory ligament of some crystals, the force of pulling the crystals is asymmetric, which makes the crystals shift in the opposite direction to the poorly developed suspensory ligament.

(1) Simple ectopic lens

There are obvious genetic tendencies, which are regular or irregular autosomal dominant inheritance, and a few are autosomal stable inheritance, often with binocular symmetry. It may be accompanied by fissure pupil deformity. The cause of dysplasia of suspensory ligament is unknown. Although intrauterine inflammation and ciliary atrophy of neuroectodermal layer are possible inducing factors, the exact mechanism is unknown. If there are abnormal development of mesodermal leaves such as extensive uveal defect, it may be related to the disorder of mesodermal leaves.

(2) Accompanied by crystal morphology and ocular abnormalities

The common ones are microspherophakia, coloboma of the lens, aniridia and so on.

(3) With congenital ectopic or dislocated lens

A, Marfan's Syndrome

It is an irregular autosomal dominant hereditary disease characterized by extensive disorder of mesodermal tissue in the whole body, characterized by abnormalities of eye, cardiovascular and skeletal systems. Marfan first reported in 1896. Ocular abnormalities are characterized by ectopic lenses, especially upward and temporal displacement. Because the lack of iris pigment layer can produce positive post-transillumination test, the local lack of pupil dilator muscle makes it difficult for drugs to dilate pupils. In addition, the eye can also have anterior chamber angle abnormality, choroidal and macular defects, and can also produce complications such as glaucoma, retinal detachment, nystagmus, strabismus and amblyopia. Bone abnormalities are found in slender bones of hands, feet and limbs, long head and thin face, unclosed foramen ovale of heart, aneurysm and aortic stenosis. Generally, there are more males than females.

B. Homodeaminuria

(Homocystinuria) is an autosomal recessive disease that most often affects bones and is characterized by osteoporosis and a tendency to develop systemic thrombosis. The lens is often dislocated under the nose, and it is easy to get rid of the anterior chamber and vitreous cavity. The tissue structure and ultrastructure of lens suspensory ligament were abnormal. The eye can also be complicated with congenital cataract, retinal detachment and degeneration, aniridia and other abnormalities. Laboratory tests can detect bleeding and homocystinuria in urine. This pathogen is caused by the lack of desulfurization ether synthase and the inability to convert homocysteine into cystine.

C, Marchesani Syndrome

It is an autosomal recessive genetic disease. Short body, short and thick limbs and fingers (toes), normal cardiovascular system. The lens is spherical, smaller than normal, and often dislocated to the lower part of the nose. After dislocation, the lens enters the anterior chamber, which is prone to glaucoma and often accompanied by refractive high myopia. Other eye abnormalities include ptosis, nystagmus, cornea and so on.

The following is a comparison of the above three syndromes (see Table 1).

Table 1 Comparison of three syndromes

Marfan syndromeMarchesani syndromeHomocysteinuria
Dislocation of lensAbove, the age of occurrence is not certain, but it can be congenital and normal in shapeMost of them are downward, which occurs after the age of 25 and is sphericalMost of them are downward, most of them occur in infancy or before the age of 25, and the shape can be normal or spherical
High intraocular pressureHappens lessEasier to occurIt is easy to happen
IntelligenceNormalNormalHalf of them are slow
Hair colorNormalNormalWith golden yellow
SkinNormal and relaxableNormalWhite, flushed zygomatic face, with reticular green spots
Cardiovascular diseaseAneurysms are prone to occur, and rupture can cause deathMost people die of cardiovascular disease after the age of 50Thrombosis may cause death
SkeletonHeight, slender limbs, spider-like toesShort body, short head and neck, big head, thick and short fingers and toesLimbs can be slender, osteoporosis and easy to fracture
MuscleUnderdeveloped muscles and less subcutaneous fatMuscle is well developed and subcutaneous fat is plumpNo specific change
Genetic modeAutosomal dominanceAutosomal dominant, sometimes incompleteAutosomal recessive
Urinary homocysteineNegativeNegativeNegative

2. Traumatic dislocation of lens

Ocular trauma, especially ocular contusion, is the most common cause of lens dislocation. Traumatic dislocation of the lens (traumatic dislocation of the lens) is often accompanied by secondary cataract formation. Dislocated crystals can be detached into anterior chamber or vitreous cavity; If accompanied by eyeball rupture, the lens can be detached under the bulbar conjunctiva.

3. Spontaneous dislocation of lens

Spontaneous lens dislocation is caused by mechanical elongation of suspensory ligament caused by intraocular lesions, or by inflammatory decomposition and degeneration. Lens dislocation caused by mechanical elongation of the suspensory ligament is common in bovine eye, staphyloma or eyeball dilatation, and can also be seen in inflammatory adhesion of ciliary body or vitreous cord pulling lens. Intraocular tumors can push and pull the lens away from its normal position. Inflammatory destruction of lens suspensory ligament can be seen in endophthalmitis or panophthalmitis, and suspensory ligament can be completely decomposed. Long-term chronic ciliary body inflammation can have the same pathological process, and the suspensory ligament can be occupied by granular tissue of ciliary body. Degeneration or malnutrition of suspensory ligament is the most common cause of natural dislocation, which is often accompanied by degeneration and liquefaction of vitreous body, such as high myopia, old choroiditis or cyclitis, and retinal detachment. Iron or copper rust, etc. can also make the suspensory ligament gradually degenerate and decompose. Another common cause is the overmaturity of senile cataract, and the degeneration of lens also involves the suspension ligament of lens. Once the suspensory ligament degenerates, the lens can be dislocated spontaneously at any time due to its own weight or slight trauma, even exertion and cough.

When the lens is dislocated, the broken suspensory ligament can be connected with the lens and gradually become turbid. Suspensory ligament is rarely severed at the end of ciliary body, but most of them are severed at the end of lens lamina, so it is rare to find suspensory ligament filament in dislocated lens.

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