I. Overview: 1. Marfan syndrome is an autosomal dominant hereditary connective tissue disorder that was proposed and named by French pediatrician Antoine-Bernard Marfan in 1896, with the causative gene located on human chromosome 15 and an incidence of 1/5000 to 1/10,000. It is characterized by extensive disorders of the mesodermal tissues throughout the body and is characterized by abnormalities of the eye, skeletal and cardiovascular systems. In addition to the characteristic ocular manifestations, the manifestations of the skeletal system mainly include long and thin body, scoliosis, elongated fingers (toes), chest wall deformity (funnel chest or chicken chest), spider’s foot-like fingers (toes), ligament laxity, abnormal joint movement, etc.; the manifestations of the cardiovascular system mainly include aortic root and ascending aorta progressive dilatation resulting in aortic closure insufficiency and intercalated aortic aneurysm, mitral valve closure insufficiency, prolapse and Aortic regurgitation, etc. The patient’s skeletal, ocular, and cardiovascular pathology and family history, any two of the four items are consistent with the diagnosis of Marfan syndrome. The most effective and simple means of diagnosing this disease are physical examination and echocardiographic ultrasound. Dilatation of the ascending aorta is the predominant feature of the disease. Epidemiological surveys show that the incidence of lens subluxation in Marfan syndrome is 60,0% to 87,2%. The abnormal development of the suspensory ligament of the lens and the subluxed lens often cause severe refractive error and visual impairment, secondary glaucoma and other complications, which in children can affect the establishment of normal visual function and lead to amblyopia. Therefore, the dislocated lens should be removed as early as possible to maximize the patient’s visual function. Removal of a hemispheric lens is usually performed by ultrasonic emulsion aspiration or lens dissection, or often in combination with an anterior vitrectomy. Depending on the extent of the lens dislocation and the surgical removal method, the following types of I0L implants are generally available: (1) standard capsular bag tension ring combined with posterior chamber IOL implantation; (2) anterior chamber iris clamping IOL implantation; (3) posterior chamber IOL fixation via scleral sutures; (4) iris suture fixation posterior chamber IOL; (5) modified hooked capsular bag tension ring combined with folded posterior chamber IOL implantation. Patients with Marfan syndrome have progressive lesions of the suspensory ligament of the lens and should, in principle, be implanted with MCTR to fix the lens capsular bag. Compared to standard CTR, it is better at maintaining the centering of the lens capsule and stability within the IOL capsule in patients with Marfan syndrome lens subluxation and at avoiding significant postoperative IOL dislocation due to progressively worsening lens suspensory ligament abnormalities. It also provides better resistance to CTR dislocation due to lens capsular bag fibrosis, wrinkling, and lens epithelial cell proliferation migration, and is more suitable for younger patients. The standard sutureless fixed hook CTR for the treatment of dislocation of the lens in Marfan syndrome, although it may achieve better near-term results, the long-term results are still to be confirmed, and it is generally not advisable to implant it, so as not to cause distant capsular bag-CTR-artificial lens complex deviation, or even complete dislocation in the vitreous cavity, unless it is pre-fixed to the standard CTR with polypropylene sutures, and then fixed to the ciliary sulcus through the equatorial part of the lens capsular bag However, the lens capsule is prone to tearing during surgery, and the force on the CTR may be uneven, requiring high operator skill. The incidence of retinal detachment in Marfan syndrome is 8% to 25 , 6%. In patients with lens subluxation, the incidence of retinal detachment is even higher after traditional lens removal surgery, ranging from 19% to 31%. Most of the causes are unstable lens or surgery resulting in pulling on the vitreous base and peripheral retinal fissure. Careful fundus examination and close follow-up should be performed before and after surgery. 2 .The significance of relevant auxiliary examinations Generally, Marfan syndrome lens subluxation can be diagnosed according to the history, symptoms and slit lamp examination results. Ultrasound biomicroscopy or OCT examination of the anterior segment of the eye: it can assist in the diagnosis and treatment of lens subluxation in Marfan syndrome, providing more specific and quantitative results such as shallow anterior chamber, iris lens contact, atrial angle closure, thinning and elongation of the lens suspensory ligament, and the extent of lens subluxation. Treatment plan and basic principles 1. Non-surgical treatment: Close follow-up is possible for lens subluxation that is still transparent and does not cause serious complications. Refractive error of crystalline origin can be corrected by convex lens or corneal contact lens to obtain part of useful vision. 2.Surgical treatment: If the scope of lens dislocation is large or the anterior capsular membrane ring tearing capsule cannot be completed, transciliary flattening/angular scleral rim lens removal combined with anterior vitrectomy is feasible, and IOL implantation can be done by transscleral fixed posterior chamber IOL implantation, anterior chamber iris clamping IOL implantation or peripheral iris suture IOL fixation. The IOL implantation is a very important part of the procedure. Anterior chamber IOL implantation is contraindicated due to complications such as distant corneal endothelial loss and secondary glaucoma. For patients with lens dislocation who can complete an anterior capsular ring tear, the ideal surgical procedure is to perform lens aspiration, MCTR, and IOL intracapsular implantation. The greatest advantage of this procedure is that it restores the normal physiological position of the lens capsule without disturbing the vitreous and reduces the occurrence of vitreoretinal complications. (1) Other congenital lens subluxation: congenital lens subluxation is generally divided into simple lens subluxation, lens subluxation with other developmental abnormalities of the eye and lens subluxation with systemic developmental abnormalities. Simple lens hemimelia has a clear genetic predisposition and is mostly autosomal dominant, with symmetrical onset in both eyes, and its cause is not clear, but it is not accompanied by other developmental abnormalities of the eye or with systemic systemic abnormalities. The cause of the disease is not clear, but it is not associated with other developmental abnormalities of the eye or with systemic abnormalities. (2) Other developmental abnormalities of the lens with systemic systemic abnormalities: Weil-Marchesani syndrome and homocystinuria are common. Marchesani syndrome is a chromosomal recessive disorder in which the patient is short and fat, with a short and thick chest, neck, fingers and toes, and abundant muscle and fat. The cardiovascular system is normal. The typical ocular manifestation is a small spherical lens with a predominantly subnasal lens dislocation, often combined with high myopia. Homocystinuria is also a chromosomal recessive disorder in which the child has increased cystine in the blood, which is excreted in the urine and is called homocystinuria. In addition to the manifestations of Marfan syndrome, it is often associated with osteoporosis and a tendency to systemic thrombosis, mental deficiency, and epilepsy. The ocular manifestations are bilateral symmetrical lens dislocation, mostly below the nose, which may be combined with congenital cataract, retinal detachment and aniridia. (3) Traumatic lens subluxation: The lens subluxation is caused by rupture of the suspensory ligament of the lens due to ocular trauma, especially blunt contusion, which usually has a clear history of trauma, mostly unilateral, and is often associated with other traumatic lesions of the eye such as traumatic cataract, atrial angle recession, secondary glaucoma or retinal concussion injury. (4) Spontaneous lens subluxation: often due to weakness of the suspensory ligament caused by ocular inflammation or degenerative disease or mechanical elongation of the suspensory ligament caused by intraocular lesions. Inflammation is seen in endophthalmitis or total uveitis, long-term chronic iridocyclitis; degeneration is seen in retinal detachment, high myopia, overmaturity cataract, pseudocapsular exfoliation syndrome, iron or copper rust; mechanical elongation is seen in bull’s eye, grapevine or dilatation of the eye is also seen in other intraocular pathologies of pulling or pushing such as ciliary inflammatory adhesions, PHPV, vitreous striae, intraocular tumors, etc.