Surgeons need to be familiar with presentations of and treatments for coloboma
Failure of the embryonic fissure to close results in congenital coloboma.
Development of the eye is a fascinating subject. Simultaneous invagination of the optic vesicle and the optic stalk creates the fetal fissure inferonasally, which then closes, beginning at the equator and proceeding anteriorly and posteriorly during the fifth to seventh week of gestation. Meanwhile, the surface ectoderm thickens to form the lens placode, which invaginates to form the lens vesicle. Simultaneously, other structures of the eye also develop. But any anomaly of closure of the embryonic fissure will result in a coloboma.
The term coloboma refers to a notch, hole or fissure in any ocular structure from a congenital malformation or an acquired process. Coloboma in Greek (koloboma) means mutilated or curtailed. Failure of the embryonic fissure to close results in the typical form of congenital coloboma. Closure defects can involve the iris, ciliary body, lens, retina, choroid, optic nerve and lid.
A colobomatous lens (Figure 1) is due to defective or absent segment of zonules, resulting in a notch in the lens. It is a misnomer in that there is no actual lenticular substance missing. There is just a retraction of a crystalline area due to localized loss of tension on the lens capsule. Intact zonules are often seen in this area, and therefore a localized area of defective ciliary body or zonules may lead to localized loss of traction on the lens capsule. It may occur along with a ciliary body coloboma. Lens coloboma is, therefore, more accurately referred to as coloboma of the zonule and/or ciliary body.
Cataract often develops at a younger age in patients with colobomatous lenses. The extent of the ocular structures affected by the coloboma should be determined preoperatively. The degree of posterior segment involvement should be confirmed by B-scan. Preoperative IOL power assessment is difficult in eyes with coloboma extending to the macula and optic disc due to high variability in axial length measurements. Small changes in the orientation of the ultrasound probe may result in different measurements. IOL selection is guided by the patient’s refraction and by measuring the distance to the patient’s preferred fixation point.
Images: Agarwal A
Endocapsular ring implantation.
Cortical aspiration in eye with lens coloboma.
Cortex removed. Note the lens coloboma and endocapsular ring.
Surgery in lens coloboma
Surgery is done using a capsular tension ring (CTR), which forms the capsular fornix (Figures 2 to 4). The CTR, which was first used by Hara et al, protects against capsular fornix aspiration, consecutive zonular dialysis, irrigation fluid flowing behind the capsule, vitreous herniating into the anterior chamber, IOL decentration and capsular phimosis. Minimal mydriasis or reactive miosis may be a problem. Conventional approaches to deal with normally positioned small pupils and cataract surgery may be used, such as mechanical stretching, iris retractors or multiple sphincterotomies. Vitreous loss may occur secondary to prolapse through the coloboma in the presence of an intact capsule. Giant retinal tears also occur with isolated lens coloboma. A large-optic IOL is advisable for better visualization of the posterior segment, which is at greater risk of potential retinal detachment, and for optimal centration of the optic relative to the ectopic pupil. Aberration-free or aspheric IOLs may also be preferable in these eyes to decrease the effect of lens decentration on vision. A silicone IOL is not advised in case a complex retinal detachment occurs that requires the use of silicone oil.
Glaucoma may sometimes be associated, and here, as in other cases, a normal trabeculectomy with phacoemulsification and IOL implantation is carried out. Congenital coloboma is often associated with microphthalmia and nystagmus. It may also be associated with orbital cyst. Well-demarcated pannus-like growths extending from the limbus onto the peripheral cornea may interfere with visualization during surgery. Phacoemulsification in these microphthalmic eyes is often a challenge, considering the relatively large size even small-gauge instruments assume in these tiny eyes. An extracapsular cataract extraction is therefore often the best option. Postoperative IOL edge glare syndrome and monocular diplopia, potential complications, can be managed by pupilloplasty. Coloboma with microphthalmos may also be associated with several genetic neurological, craniofacial or other multisystem developmental defects. CHARGE syndrome consists of coloboma, heart defects, choanal atresia, retardation, genital anomalies, and ear or hearing abnormalities.
Eyes with congenital coloboma and cataract are at greater risk of surgical complications. The condition may be associated with nondilating pupil, zonular absence, etc. The structural integrity of the globe may be compromised, increasing the risk of vitreous loss during cataract extraction.
The iris coloboma is repaired using two peripheral corneal stab incisions on either side of the inferior coloboma. Using Vannas scissors, two small cuts are made through the inferior iris sphincter on either side. A straight needle on a 10-0 Prolene suture is passed through the paracentesis and then edges of the central iris leaflets, exiting through the distal peripheral corneal stab incision. It is then tied with a modified Siepser sliding knot technique. Iris tissue peripheral and central to the first knot is also closed in a similar technique to get a round, satisfactory pupil. Severing the iris sphincter inferiorly releases the pupil’s attachment to the iris base and chamber angle. The pupil constricts normally after re-approximation of the central sphincter leaflets and no longer moves inferiorly. A cosmetic contact lens is another alternative for monocular diplopia. Postoperative anterior capsular fibrosis may also solve this problem.
In summary, lens colobomas can occur as isolated defects or with anterior and posterior segment involvement. The anterior segment surgeon needs to be familiar with the various presentations, respective management protocols, and the preoperative and technical intraoperative challenges in each situation.
For more information:
- Amar Agarwal, MS, FRCS, FRCOphth is director of Dr. Agarwal’s Group of Eye Hospitals. Prof. Agarwal is the author of several books published by SLACK, Incorporated, publisher of Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery, and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; fax: 91-44-28115871; e-mail: email@example.com; Web site: www.dragarwal.com.
- Agarwal A. Handbook of Ophthalmology. Thorofare, NJ: SLACK Incorporated; 2005.
- Agarwal A. Phaco Nightmares: Conquering Cataract Catastrophes. Thorofare, NJ: SLACK Incorporated; 2006.
- Agarwal S, Agarwal A, Agarwal A. Phacoemulsification –Two volume set. 3rd ed. Informa Healthcare; 2004.