Management of Subluxated cataract
Dr. Ruchi Goel,
Assistant Professor, Gurunanak Eye Center, Maulana Azad Medical College, New Delhi
Email:gruchi@rediffmail.com
Dr. KPS Malik
Additional Director General Health Services, CHS, and Head of Ophthalmology Safdarjung Hospital, Vardhman Mahavir Medical College, New Delhi
Zonular compromise complicates every step of cataract surgery and poses a serious challenge in terms of safety and visual outcome. When the lens is displaced from its normal position, it is considered subluxated if it remains in the pupillary area and luxated or dislocated if it is completely displaced from the pupil. Ectopia lentis is the term used to describe congenital dislocations.1 Lens displacements may be traumatic, heritable, and spontaneous.( Table 1)
| Table 1: Causes of Lens Dislocatiotion | ||
Causes |
Features |
|
Traumatic |
Responsible for >50% lens displacements |
|
Heritable
|
Associated systemic |
Marfans’s syndrome: Triad of skeletal, cardiovascular & ocular anomalies. Autosomal dominant. Generalized thinness and elongation of limbs, sternal deformities, kyphoscoliosis, joint hyperextensibility, low ratio between upper and lower segment, arachnodactyly, cardiopathy, aortic dilatation, dissecting aneurysm, mitral regurgitation. Ectopia lentis: B/L superotemporally, usually partial, rarely progressive. Hypoplasia of dilator muscle, myopia is common. Angle abnormalities: Iris processes, pectinate ligaments, vascular anomalies. |
Homocystinuria: Inborn error of sulphur containing aminoacids, Sodium nitroprusside test of urine is used for screening. Autosomal recessive. Tall, slender, genu valgum, flat feet, kyphoscoliosis, joint laxity, deformed sternum, generalised osteoporosis with vertebral collapse, high arched palate, malar flush, light, fair & dry skin, fair and sparse hair. Mental retardation >50% of cases, thromboembolic phenomenon in veins & middle sized arteries, premature death in 40% cases. Ectopia lentis: downwards & nasal; progressive. Angle anomalies donot occur. Glaucoma and retinal detachment may occur. |
||
Weil-Marchesani syndrome: Dominant and recessive inheritance. Brachymorphy, short stature, spade like hands and feet, large thoraces, reduced joint motility. No cutaneous, vascular, mental or urinary abnormality. Microspherophakia, lens displacements later in life. |
||
Other disorders: Hyperlysinemia, Ehlers-Danlos syndrome, Sturge Weber syndrome, Crouzon’s syndrome, chondrodysplastic, dwarfism, oxycephaly, polydactyly, sulfite oxidase deficiency. |
||
Associated ocular anomalies |
Ectopia lentis et pupillae, aniridia, isolated anomaly. |
|
Spontaneous |
Old age, high myopia, endophthalmitis, treatment of retinal detachment by diathermy, Eale’s disease, chalcosis, buphthalmos, megalocornea, coloboma of iris/choroids, perforation of corneal ulcer and growth of intraocular tumor. |
|
The adoption of new devices and techniques that minimize the stress on compromised zonules have gained acceptance over older approaches like iridectomy, laser iridotomy and intracapsular cataract extraction. The contemporary techniques of management shall be discussed at length.
Anatomy
The lens is suspended in its anatomic position by ciliary zonules (zonules of Zinn or suspensory ligament of Zinn) which consists of fibers which run from ciliary body and fuse into the outer layer of the lens capsule around the equatorial zone. The bundles that insert into the anterior capsule are stronger than those that insert in the posterior capsule. The insertion of zonules extends 1.5 mm anterior to the equator and 1mm posterior to it. Each zonule measures 5 to 30µm in diameter and is composed of bundles of microfibrils. Biochemically they are composed of fibrillin, a protein product of the gene linked to Marfan’s syndrome.
Preoperative Evaluation
A detailed ocular examination is mandatory. Both near and distant BCVA should be determined, keeping in mind that the patient may best see with an aphakic correction if the lens is markedly subluxated. The exact degree of zonular loss, location of defect and presence or absence of vitreous in the anterior chamber should be noted. Ultrasound biomicroscopy and anterior segment OCT, are especially useful for zonular and angle assessment in patients where the pupil fails to dilate. An inferior subluxation often indicates 360 degrees of zonular insufficiency combined with the effect of gravity. Gonioscopy is performed to note any developmental defects, pseudoexfoliative material and deformities secondary to trauma or as a sequlae to subluxation. The fundus examination is done to look for lattice degeneration, cyclitic membranes, retinal detachment or posttraumatic pathology. Retinal detachments occur in 10% eyes with Marfan’s syndrome and Homocystinuria.2 Bscan ultrasonography is indicated in opaque ocular media.(Figure 1) Presence if any of uveitis, glaucoma, corneal edema and amblyopia should also be ascertained.
Fig1: Bscan showing posteriorly subluxated cataract and a normal posterior segment.
Besides the routine systemic examination, conscious efforts are directed towards detection of any cardiovascular abnormalities especially in Marfan’s syndrome and Homocystinuria.
Indications for surgery
- In younger children if there is significant or progressive dislocation or if amblyopia cannot be effectively treated by conventional means such as glasses, contact lens, and/or patching.
- For older children and adults, if poor visual acuity is attributed to subluxated lens and is not amenable to spectacle correction, or if the lens is threatening to dislocate anteriorly or posteriorly.
- Lens induced uveitis.
- Significant cataract.
Operative procedure:
Fig 2 :Superior zonular dehiscence.
|
|
Degree of Zonular dehicense |
Procedure chosen |
|---|---|
Superior upto 4 clock hours |
First choice: CTR with IOL implantation |
Second choice: IOL implantation with haptic being used to stretch the bag ( Figure 2 & 3) |
|
Inferior upto 3 clock hours |
CTR with IOL implantation |
Anywhere> 3 to 6 clock hours |
Modified CTR with single loop |
Anywhere >6 to >9 clock hours |
Modified CTR with double loop with IOL implantation |
9 or more clock hours /generalized weakness of zonules |
Intracapsular cataract extraction with scleral fixated IOL/Iris fixated IOL/anterior chamber IOL |
Depending on the degree of subluxation the surgical procedure is chosen. (Table 2) In 1991, the CTR(capsular tension ring) was introduced by Dr Hara and subsequent studies demonstrated that CTR could provide both intraoperative and postoperative stabilization of capsular bag and IOL.3 These PMMA rings can be inserted anytime after the capsulorrhexis has been completed.4 In patients with profound and progressive zonular loss , Osher described the technique of suturing CTR to the scleral wall by straddling the CTR with a 10,0 prolene suture, double armed with CIF-4 needles.5 This procedure involved the risk of rupturing the bag. The modified CTR(MCTR), designed by Dr Robert Cionni, incorporates a unique fixation hook to provide scleral fixation without violating the integrity of the capsular bag.6 The MCTR consists open, flexible PMMA filament with a fixation hook that loops anteriorly and in a second plane wrapping around the capsulorrhexis edge. At the free end of the hook is an eyelet through which a suture can be passed for scleral fixation. Depending on the extent of subluxation single or double loop models can be chosen.( Figure 4)The MCTR has shown to provide a good centration of capsular bag.7
Fig 3: The superior haptic of IOL used to strech the capsular bag.( Courtesy: Malik & Goel.Manual os Small Incision Cataract Surgery2003)
Fig 4:Capsular tension ring & Modified capsular tension ring.
