bubble_chart Overview

Under normal circumstances, the lens is suspended from the ciliary body by the zonule of Zinn, with its axis nearly aligned with the visual axis. Due to congenital factors, trauma, or pathological conditions, defects or ruptures in the zonule can weaken the suspensory force, leading to ectopia lentis or subluxation of the lens. If the zonule is completely ruptured, it can result in complete dislocation of the lens.

bubble_chart Etiology

Abnormal lens position can be caused by congenital developmental anomalies. If the lens is not in its normal position at birth, it is called lens ectopia; if the lens position changes after birth due to congenital factors, trauma, or pathological changes, it can generally be referred to as lens dislocation (lens dislocation) or subluxation (lens subluxation). However, in cases of congenital lens position abnormalities, it is sometimes difficult to determine when the lens position changed. Therefore, the terms lens dislocation and ectopia are not strictly distinguished and are often used interchangeably.

I. Congenital Lens Ectopia or Dislocation

This can occur as an isolated congenital anomaly, or it may be associated with corectopia and other ocular abnormalities, or it may be part of a systemic syndrome involving mesodermal, particularly skeletal, developmental anomalies. In all cases, the condition is often due to weakness in part of the zonular fibers, leading to asymmetric traction on the lens, which then shifts toward the side with weaker zonular support.

(1) Simple Lens Ectopia

This condition has a significant hereditary tendency, typically following a regular or irregular autosomal dominant inheritance pattern, with a few cases being autosomal recessive. It is often bilateral and symmetrical. It may be accompanied by slit-like pupil deformities. The cause of zonular hypoplasia remains unclear. Although intrauterine inflammation or atrophy of the neuroectodermal ciliary body may be contributing factors, the exact mechanism is unknown. If associated with extensive uveal defects or other mesodermal developmental anomalies, it may be related to mesodermal developmental disorders.

(2) Associated with Lens Morphology and Ocular Abnormalities

Common manifestations include microspherophakia, coloboma of the lens, and aniridia.

(3) Associated with Congenital Lens Ectopia or Dislocation

1. Marfan Syndrome: An irregular autosomal dominant disorder characterized by widespread mesodermal tissue abnormalities, primarily affecting the eyes, cardiovascular system, and skeletal system. First described by Marfan in 1896. Ocular abnormalities include lens dislocation, particularly upward and temporally. Due to absence of the iris pigment layer, a positive transillumination test may be observed, and the pupil may be difficult to dilate due to partial absence of the dilator muscle. Other ocular features may include abnormal anterior chamber angles, choroidal and macular defects, as well as complications such as glaucoma, retinal detachment, nystagmus, strabismus, and amblyopia. Skeletal abnormalities include slender limbs, dolichocephaly, and a long, thin face. Cardiovascular anomalies include patent foramen ovale, aortic aneurysm, and aortic stenosis. Males are more commonly affected than females.

2. Homocystinuria: An autosomal recessive disorder most commonly affecting the skeletal system, characterized by osteoporosis and a tendency toward systemic thrombosis. The lens typically dislocates downward and nasally and may easily dislocate into the anterior chamber or vitreous cavity. The zonular fibers show abnormal structural and ultrastructural changes. Ocular associations may include congenital cataracts, retinal detachment and degeneration, and aniridia. Laboratory tests reveal homocystine in the blood and urine. The condition is caused by a deficiency of cystathionine synthase, impairing the conversion of homocysteine to cysteine.

3. Marchesani Syndrome: An autosomal recessive disorder characterized by short stature, brachydactyly, and normal cardiovascular system. The lens is spherical and smaller than normal, often dislocating downward and nasally. Dislocation into the anterior chamber may lead to glaucoma, often accompanied by high myopia. Other ocular abnormalities include ptosis, nystagmus, and microcornea.

Below is a comparison of the three syndromes (see Table 1).

Table 1 Comparison of the Three Syndromes

	Marfan syndrome	Marchesani syndrome	Homocystinuria
Lens dislocation	Upward, age of occurrence varies, can be congenital, normal morphology	Mostly downward, occurs after age 25, spherical shape	Mostly downward, often occurs in childhood or before age 25, morphology can be normal or spherical
High intraocular pressure	Less likely to occur	More likely to occur	Very likely to occur
Intelligence	Normal	Normal	Half are delayed
Hair color	Normal	Normal	Golden
Skin	Normal, may be loose	Normal	Fair, flushed cheeks, may have livedo reticularis
Cardiovascular disease	Prone to aortic aneurysm, rupture can be fatal	Often die from cardiovascular disease after age 50	Prone to thrombosis, potentially fatal
Skeleton	Tall, slender limbs, arachnodactyly	Short stature, short neck, large head, short and thick fingers/toes	Limbs may be slender, osteoporosis, prone to fractures
Muscles	Underdeveloped muscles, thin subcutaneous fat	Well-developed muscles, ample subcutaneous fat	No specific changes
Inheritance pattern	Autosomal dominant	Autosomal dominant, sometimes incomplete	Autosomal recessive
Urine homocysteine	Negative	Negative	Negative

II. Traumatic lens dislocation

Ocular trauma, especially blunt contusion, is the most common cause of lens dislocation. Traumatic dislocation of the lens is often accompanied by secondary cataract formation. The dislocated lens may enter the anterior chamber or vitreous cavity; if accompanied by eyeball rupture, the lens may dislocate under the conjunctiva.

III. Spontaneous lens dislocation

Spontaneous lens dislocation is caused by mechanical elongation of the zonules due to intraocular lesions, or by inflammatory decomposition and degeneration. Lens dislocation due to mechanical elongation of the zonules is commonly seen in buphthalmos, staphyloma, or eyeball expansion, and may also occur due to adhesions from ciliary body inflammation or vitreous strands pulling on the lens. Intraocular tumors can push or pull the lens out of its normal position. Destruction of the lens zonules by inflammation is observed in endophthalmitis or panophthalmitis, where the zonules may completely decompose. Long-term chronic ciliary body inflammation can lead to the same pathological process, with the zonules being replaced by granulation tissue from the ciliary body. Degeneration or dystrophy of the zonules is the most common cause of natural lens dislocation, often accompanied by vitreous degeneration and liquefaction, such as in high myopia, old chorioretinitis or cyclitis, or retinal detachment. Conditions like siderosis or chalcosis can also gradually degenerate and decompose the zonules. Another common cause is the hypermature stage of senile cataract, where degenerative changes in the lens also affect the zonules. Once the zonules degenerate, the lens may dislocate spontaneously at any time due to its own weight, minor trauma, or even exertion and coughing.

When the crystalline lens dislocates, the broken zonules may remain attached to the lens and gradually become opaque. The zonules rarely detach from the ciliary body end, but mostly detach from the lens lamellar end. Therefore, it is rare to find zonular fibers on a dislocated lens.

bubble_chart Clinical Manifestations

According to the degree and morphology of crystalline lens dislocation, it can be divided into incomplete dislocation and complete dislocation of the crystalline lens.

I. Incomplete dislocation of the crystalline lens

The displaced lens remains in the pupillary area or within the vitreous cavity behind the plane of the iris. The symptoms of incomplete dislocation depend on the extent of the lens displacement. If the axis of the lens remains on the visual axis, only lens-induced myopia occurs due to loosening of the suspensory ligaments and increased curvature of the lens. If the lens axis tilts horizontally, vertically, or obliquely, it can cause severe astigmatism that is difficult to correct with glasses or contact lenses. A more common form of incomplete dislocation is longitudinal displacement of the lens, which may result in monocular diplopia. Slit-lamp examination of the eye may reveal deepening of the anterior chamber, iris tremor, a grayish lens, visible equatorial regions or even ruptured suspensory ligaments, and vitreous herniation into the anterior chamber with pigment on the surface. Fundoscopy may show a crescent-shaped fundus reflex and double fundus images.

II. Complete dislocation of the crystalline lens

The displaced lens completely leaves the pupillary area, and the lens may shift or result in:

(1) Pupillary incarceration;

(2) Dislocation of the lens into the anterior chamber;

(3) Dislocation of the lens into the vitreous cavity, floating on or sinking into the vitreous;

(4) Dislocation of the lens through a retinal hole into the subretinal or sub-scleral space;

(5) Dislocation of the lens through a corneal ulcer perforation or scleral rupture into the subconjunctival or sub-tenon space.

Complete dislocation of the lens is more severe than incomplete dislocation. The lens may dislocate into the pupillary area, causing pupillary incarceration, often occurring after trauma when the lens axis rotates 90°, with the equator of the lens located in the pupillary area or even a 180° rotation, with the anterior surface of the lens facing the vitreous.

After the lens completely leaves the pupillary area, vision becomes aphakic, the anterior chamber deepens, and iris tremor occurs. The dislocated lens may move with changes in body position in the early stages. If the lens dislocates into the anterior chamber, it settles at the bottom of the deepened anterior chamber, with a smaller diameter than in its normal position but increased convexity. A transparent lens appears as an oil droplet with golden shimmering edges, while an opaque lens appears as a white disc. However, during the process of the lens moving from the vitreous cavity through the pupil into the anterior chamber, partial pupillary block may occur, leading to acute glaucoma. If the pupillary area remains clear, good vision can be maintained, and the patient may tolerate it well. Sometimes, vision may improve in cases of hypermature cataract when the lens dislocates into the anterior chamber, and the lens in the anterior chamber may gradually be absorbed. However, more commonly, repeated contact between the lens and the cornea can lead to severe iridocyclitis, corneal dystrophy, and acute glaucoma. Dislocation of the lens into the vitreous cavity is more common than into the anterior chamber, and patients may tolerate it better, but the long-term prognosis remains uncertain.

The outcome of a dislocated lens varies from person to person. Many dislocated lenses can remain transparent for years. However, dislocated lenses tend to degenerate over time: epithelial cells gradually break down, cortical water clefts form, the cortex becomes opaque and liquefies, the lens capsule shrinks, and the nucleus sinks, forming Morgagnian cataract. Partial or complete absorption of the lens is rare.

bubble_chart Treatment Measures

1. Overview

The treatment of crystalline lens dislocation is challenging. Removing a dislocated lens carries higher risks than extracting a typical white internal visual obstruction, and blind surgery may lead to visual impairment or even loss of the eyeball. Therefore, treatment plans must be carefully considered. The management of lens dislocation depends on factors such as the position of the lens, its hardness, the visual acuity of the affected and contralateral eye, the patient's age, the presence of congenital abnormalities, complications, and surgical conditions. The causes of vision loss due to lens dislocation are multifaceted, including opacities in the refractive media, secondary glaucoma, and congenital retinal abnormalities. Thus, lens extraction does not always guarantee improved vision.

For incomplete lens dislocation without complications, treatment involves correcting refractive errors in the phakic or aphakic zones using spectacles or contact lenses to restore adequate vision. Since astigmatism in the phakic zone is often irregular and difficult to correct, optical correction in the aphakic zone usually yields better results. If the aphakic zone is small and the anterior chamber is deep, weak mydriatics can be used to maintain pupil dilation, or laser iridotomy can be performed to enlarge the aphakic zone, facilitating refractive correction.

2. Indications for Surgical Treatment

Generally, the indications for surgical lens extraction include:

1. Lens dislocation severely impairing vision, especially when accompanied by white internal visual obstruction;

2. Lens dislocation into the anterior chamber;

3. Phacolytic glaucoma;

4. Phacoanaphylactic uveitis;

5. Pupillary block glaucoma unresponsive to conservative treatment or conventional glaucoma surgery;

6. Lens opacity hindering examination or surgery for retinal detachment.

7. Dislocated lens in the hypermature or mature stage of white internal visual obstruction.

3. Surgical Treatment

Preoperative preparation and anesthesia are the same as for white internal visual obstruction extraction.

During lens extraction, extreme care must be taken to minimize vitreous loss. Preoperative use of carbonic anhydrase inhibitors or hyperosmotic agents to reduce intraocular pressure is recommended, and a Flieringa ring may be sutured in place beforehand. The following methods can be employed for lens extraction:

(1) Cryoextraction and Silicone Lens Extraction

For lenses dislocated into the anterior chamber, preoperative miotics should be administered. A corneal limbal incision is made, and the lens is extracted using cryoextraction or silicone adhesion, similar to intracapsular cataract extraction. For subluxated lenses partially in the pupil and anterior chamber with surrounding vitreous, a small incision is first made for anterior vitrectomy to clear vitreous from the anterior chamber. The incision is then enlarged for intracapsular cryoextraction.

(2) Lens Aspiration

For young patients with grade I incomplete lens dislocation and no hard nucleus, a small limbal incision is made to introduce a cystotome to rupture the anterior capsule (or Nd:YAG laser capsulotomy may be used). An irrigation-aspiration needle is then used to remove the lens cortex. If necessary, a second incision can be made at the temporal or superior limbus to stabilize the lens during capsulotomy and aspiration. If posterior capsule rupture or vitreous prolapse occurs, an anterior vitrectomy can be performed to remove vitreous and residual cortex.

(3) Pars Plana Lensectomy

For subluxated lenses, a pars plana approach can be used with a vitrector to excise the lens (similar to the surgical treatment of white internal visual obstruction described in Chapter 2, Section 7.2 of this volume). For harder lenses, phacoemulsification may be performed.

For lenses dislocated into the vitreous cavity, the most effective method is pars plana vitrectomy with the aid of an endoilluminator to excise the lens.

(4) Use of Perfluorocarbon for Extracting Dislocated Lenses in the Vitreous Cavity

Perfluorocarbon (Perfluorocarbon) liquid is heavier than water and has low viscosity. After vitrectomy, it can be injected in front of the retina to float the lens and push it into the pupillary area, allowing conventional extraction.

(5) Cryoextraction of the lens in the vitreous cavity

For a completely dislocated lens in the vitreous, it can be removed via an open or vitrectomy approach, followed by inserting a cryoprobe into the vitreous cavity to extract the lens. However, this method carries certain risks and is not commonly used.

(6) Lens loop delivery of the lens in the anterior chamber or vitreous cavity

In the absence of cryoextraction or vitrectomy equipment, the dislocated lens in the anterior chamber can be fixed by constricting the pupil. A lens loop is then inserted through the corneal limbal incision behind the lens to deliver it. For a lens dislocated into the vitreous cavity, BSS is gently injected through the corneal limbal incision toward the ciliary body, allowing the lens to float up from the opposite side. A lens loop is then inserted to lift and deliver the lens.

(7) Bimanual needle technique for removing a dislocated lens in the vitreous

In the absence of vitrectomy equipment, for a lens dislocated into the posterior vitreous, the patient is instructed to assume a head-down or prone position until the lens settles near the posterior pupillary margin. Two sharp, long needles (Barraquer needles) are then inserted through the pars plana, passing behind the lens to the opposite sclera, trapping the lens in the pupillary area. The patient is then repositioned supine, and an anterior chamber incision is made at the corneal limbus to extract the lens using a cryoprobe or lens loop. Residual vitreous in the anterior chamber is excised. This method may lead to complications such as vitreous hemorrhage and retinal detachment and should only be used cautiously when vitrectomy equipment is unavailable.

bubble_chart Complications

In addition to causing severe refractive errors, crystalline lens dislocation often leads to some serious complications.

1. Uveitis

is a common complication of lens dislocation. There are two types of uveitis caused by lens dislocation. One is triggered by mechanical irritation of the uveal tissue by the dislocated lens, while the other occurs when the dislocated lens becomes hypermature, leading to lens-induced uveitis. Both types of uveitis are stubborn inflammations and may result in secondary glaucoma.

2. Secondary glaucoma

is also one of the most frequent complications. When the lens dislocates into the pupillary area or a vitreous hernia becomes incarcerated in the pupil, pupillary block glaucoma may occur. Repeated pupillary block can cause iris bombe, leading to aphakic malignant glaucoma. Long-term lens dislocation may also cause phacolytic glaucoma. Additionally, lens dislocation caused by blunt ocular trauma may be accompanied by iridodialysis or angle recession, resulting in secondary glaucoma.

3. Retinal detachment

is the most common and severe complication of lens dislocation, particularly in eyes with congenital abnormalities such as Marfan syndrome, where it may even occur bilaterally. Treating retinal detachment caused by lens dislocation is challenging because the dislocated lens often obstructs the accurate localization of retinal breaks and the extent of detachment. If the lens is removed first, it may lead to vitreous loss, worsen retinal pathology, and delay the timing of retinal reattachment surgery.

4. Corneal opacity

In recent years, it has been noted that lens dislocation can cause corneal opacity. When the dislocated lens enters the anterior chamber and comes into contact with the corneal endothelium, it can damage the endothelial cells, leading to corneal edema and opacity.