Is it a coloboma or not? A new definition for isolated lens coloboma: focal zonular dysgenesis

Nicole B Larivoir; Paula M Marinho; Ivan C Teixeira; Gabriel B De Figueiredo; Rodrigo A B. Fernandes; Lincoln L Freitas

doi:10.4103/pajo.pajo_15_23

ORIGINAL ARTICLE

Year : 2023 | Volume : 5 | Issue : 1 | Page : 16

Is it a coloboma or not? A new definition for isolated lens coloboma: focal zonular dysgenesis

Nicole B Larivoir¹, Paula M Marinho², Ivan C Teixeira³, Gabriel B De Figueiredo⁴, Rodrigo A B. Fernandes⁵, Lincoln L Freitas⁵
¹ Department of Ophthalmology, Federal University of Juiz de Fora, MG, Brazil
² Vision Institute, IPEPO; Department of Ophthalmology, Federal University of Sao Paulo, Brazil
³ Department of Ophthalmology, Santa Casa de Sao Paulo; Sao Paulo Eye Hospital, H.Olhos, SP, Brazil
⁴ D'Olhos Day Hospital, SP, Brazil
⁵ Department of Ophthalmology, Federal University of Sao Paulo, SP, Brazil

Date of Submission	14-Mar-2023
Date of Decision	21-Mar-2023
Date of Acceptance	24-Mar-2023
Date of Web Publication	11-May-2023

Correspondence Address:
Nicole B Larivoir
MD, Rua Pedro Scapim 165/202, São Matheus, Juiz de Fora, Minas Gerais
Brazil

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/pajo.pajo_15_23

Abstract

Purpose: Ocular coloboma is defined as a congenital malformation caused by defective closure of the fetal fissure, resulting in a notch in any structure. However, the entity known as “isolated lens coloboma” does not seem to have a similar etiological basis with other ocular colobomas. This congenital malformation can induce an important decrease of the visual acuity, and facectomy has an increased risk for intraoperative and postoperative complications. Better surgical planning could be achieved with an accurate definition of the diagnosis and pathophysiology of this lens abnormality, as the extent and mechanism of zonular disease will have a significant impact on the selection of the modality of intervention.
Methods: Nine eyes of seven patients, who were diagnosed with “isolated lens coloboma” and underwent phacoemulsification and implant of intraocular lens (IOL), were studied (retrospective case series). The surgeries were performed by four different surgeons, according to their preferred technique, in the last 5 years.
Results: There were no intraoperative complications. Two (22.22%) eyes presented postoperative complications, one of which was the IOL decentralization.
Conclusion: Considering the ocular morphogenesis and the definition of coloboma, the ideal denomination for the congenital malformation traditionally known as isolated lens coloboma would be “focal zonular dysgenesis.” The best surgical approach, contemplating the pathophysiology, in addition to the cases described and review of literature, is discussed.

Keywords: Cataract, coloboma, intraocular, lenses, lens diseases, phacoemulsification

How to cite this article:
Larivoir NB, Marinho PM, Teixeira IC, De Figueiredo GB, B. Fernandes RA, Freitas LL. Is it a coloboma or not? A new definition for isolated lens coloboma: focal zonular dysgenesis. Pan Am J Ophthalmol 2023;5:16

How to cite this URL:
Larivoir NB, Marinho PM, Teixeira IC, De Figueiredo GB, B. Fernandes RA, Freitas LL. Is it a coloboma or not? A new definition for isolated lens coloboma: focal zonular dysgenesis. Pan Am J Ophthalmol [serial online] 2023 [cited 2023 May 30];5:16. Available from: https://www.thepajo.org/text.asp?2023/5/1/16/376675

Introduction

Coloboma is derived from the Greek koloboma, meaning mutilated or curtailed.^[1] Ocular coloboma is traditionally defined as a congenital malformation caused by defective closure of the fetal fissure during early eye morphogenesis, resulting in a notch, gap, hole, or fissure in any of the ocular structures.^[1]

The entity traditionally known as isolated lens coloboma is rare and characterized by notching of the equator of the lens.^[2] Despite the name, it does not seem to have a similar etiological basis with other ocular colobomas, as the lens vesicle develops independent of the embryonic fissure.^[3] Moreover, there is no real tissue defect in the lens itself. Instead, the lens is thicker and more spherical in that area, probably due to zonular dysgenesis and isolated weakness.^[4] Furthermore, the capsular bag is intact.

This congenital malformation can induce an important decrease of the visual acuity due to the presence of cataract and/or high lenticular astigmatism.^[4],[5] Cataract surgery in these eyes has an increased risk for intraoperative and postoperative complications, considering the deficient zonular support and the deformity of the capsular bag. Better surgical planning could be achieved with a better definition of the diagnosis, as the extent and mechanism of zonular disease will have a significant impact on the selection of the modality of intervention.

The aim of this study is precisely to define the accurate diagnosis and pathophysiology of this lens abnormality.

Methods

This study was a retrospective analysis of a small case series of seven patients who were diagnosed with “isolated lens coloboma” and nuclear sclerosis. They underwent phacoemulsification and implant of intraocular lens (IOL) by four experienced and different surgeons, in multiple centers, in the last 5 years. The surgical technique used for the stabilization and centering of IOL was chosen according to the patient's clinical examination and the surgeon's preference, supported by the available publications. The Institutional Review Board/Ethics Committee from Universidade Federal de São Paulo approved the study protocol (42054720.7.0000.5505).

Results

The patient data are shown in [Table 1]. The patients had a median age of 38.14 years, and 6 (85.71%) patients were male. All patients presented a progressive decrease in vision acuity, and in only one of them (14.86%), the complaint was unilateral. There was no positive familiar history or any systemic disease. After pupillary dilatation, slit-lamp biomicroscopy revealed straight inferior equator of the lens with scanty zonules [Figure 1]. None of them had uveal or retinochoroidal coloboma, and fundus examination showed normal outcomes. Phacoemulsification and IOL implantation were performed by experienced surgeons, and there were no intraoperative complications.

Figure 1: Preoperative slit-lamp biomicroscopy of four different patients showing straight inferior equator of the lens with scanty zonules

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Table 1: Patient data

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Considering the nine cases reported in the present study, only two of them (cases 2 and 9) presented with <120° of defect. In case 2, IOL was implanted in the capsular bag with standard capsular tension ring (CTR), without decentration in the postoperative [Figure 2]. In case 9, IOL was placed in the bag without any capsular support device, but good stabilization was accomplished as well.

Figure 2: Pre- (a) and postoperative (b) slit-lamp biomicroscopy showing centered IOL and CTR in the capsular bag. IOL: Intraocular lens, CTR: Capsular tension ring

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Regarding the cases with more than 120° of defect, IOL was placed in the capsular bag in three of them (cases 1, 3, and 4). The best results concerning IOL centration were achieved with modified CTR with scleral fixation (cases 1 and 3). In case 4, which presented a defect of 180°, the use of a standard CTR was associated with superior IOL decentration, which is compatible with the results of the literature described above [Figure 3].

Figure 3: Pre- (a) and postoperative (b) slit-lamp biomicroscopy showing IOL decentralization. IOL: Intraocular lens

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In cases 5 and 6, considering that the extension of the defect was 180° and only standard CTR was available, sulcus IOL placement with standard CTR implant inside the capsular bag was performed, with good centration in the postoperative. In cases 7 and 8, the unavailability of any kind of CTR led the surgeon to implant the IOL in the ciliary sulcus, and satisfactory centering was achieved.

Discussion

Normal ocular morphogenesis initiates with the bilateral evagination of the optic vesicles from the neuroectoderm of the developing brain from 21 to 25 days of gestation. Within about 30 days, as the optic vesicle reaches the surface ectoderm, its ventral surface begins to invaginate, forming a double-layered optic cup. At the same time, a groove is formed along the length of the ventral aspect of the optic cup and optic stalk, referred to as the fetal or embryonic fissure.^[1],[6] Concurrently, the surface ectoderm thickens to form the lens placode, which invaginates to form the lens vesicle.^[1],[6]

By the 5^th week of gestation, the margins of the fetal fissure displace the periocular mesenchyme to fuse in the central region of the fissure and proceed proximally along the optic stalk and distally toward the optic cup rim. Fissure closure is complete by 7 weeks of gestation.^[1],[6]

The fibers from the zonula are derived from the tertiary vitreous, generated by the neural ectoderm at the margin of the optic cup during the 3^rd to 4^th month of gestation.^[7] The primary candidate for synthesis of the zonule is the ciliary nonpigmented epithelium, and the mechanisms and factors guiding their highly oriented and predictable attachment to sites on the lens capsule are still unknown.^[8]

Ocular coloboma is traditionally defined as a congenital ocular malformation caused by partial or complete failure of the embryonic fissure to close, resulting in a notch, gap, hole, or fissure in any of the ocular structures. Typically, this is seen as a ventral gap in the iris, but it can also affect the retina, choroid, and optic nerve, depending on the moment of development when there was a failure to close the fissure.^[6]

As demonstrated, the lens vesicle derivates from the surface ectoderm and develops independent of the embryonic fissure, which would make the term “lens coloboma” inappropriate.^[3] Furthermore, there is no real tissue defect in the lens itself; instead, the lens is thicker and more spherical in the area adjacent to the defect.^[9]

It seems that this malformation results from focal faulty development of the zonule, which may be absent or weak, resulting in released tension on the lens capsule and segmental contraction of the affected region.^{[2],[5],[9],[10]} Thereafter, many authors believe that the correct name for this malformation should be “zonular coloboma.”^[11] However, the zonular development occurs after the closure of fetal fissure; also, there are cases with only zonular weakness instead of zonular absence, which would speak against the definition of coloboma.

Therefore, the most appropriate denomination for this ocular malformation would be “focal zonular dysgenesis.” Although the etiology is not fully understood, it is believed that it can be inherited^[6] or result from 3^rd to 4^th-month embryonic exposure to toxic agents or inflammation,^[2] sectoral persistent vasculature vessels,^[11],[12] or ciliary body cyst.^[11]

Although the condition is rare, the reported types are of considerable diversity. The edge of the lens defect may be straight, indented, curved in or projecting out,^[13] depending on the extension zonular involvement and if it affects the anterior, posterior or equatorial fibers.^[14] Most reported cases show the defect to downward, or down and slightly in or out, but it can involve any of the regions in the lens.^[13],[15]

The congenital zonular dysfunction can induce an important decrease of the visual acuity due to high lenticular astigmatism induced and the development of cataract at much earlier ages.^[4],[5],[15] Cataract surgery in these eyes has an increased risk for intraoperative and postoperative complications, considering the deficient zonular support and the deformity of the capsular bag. It is recommended to plan the cataract surgery in the early stages of nuclear sclerosis, as postponement would only lead to a more challenging surgical scenario.^[15],[16] Phacoemulsification should be a technique of choice, as it has been found to be safer than manual small-incision cataract surgery in these cases.^[3]

In the preoperative assessment, it is necessary to determine the extent of the zonular fragility, the presence of phacodonesis, and the size of dilated pupil.^[16],[17] An important point to consider in surgical planning, based on the pathophysiology under discussion, is that the zonular stretching is localized and not related to qualitative or quantitative abnormalities in zonular components such as fibrillin,^[8] since it can modify the modality of intervention. It is also of interest to highlight that the capsular bag, despite being intact, presents segmental contraction due to zonular dysgenesis, being usually smaller than normal.

During the surgery, the main challenges are the laxity of zonules, which can pose problems during the confection of the capsulorhexis (capsular hooks can be used to center and stabilize the capsule, mainly when the zonular dysfunction is wider than 120°^[5],[18]); the possibility of vitreous loss secondary to prolapse through the coloboma in the presence of an intact capsule; and the difficult of stabilization and centration of IOL.^[3],[17]

Capsular support devices, such as CTRs, have been found to be an effective option to stabilize the capsular bag and stretch the defective lens equator in the notching region, helping the IOL to keep centered.^{[10],[11],[12]} They also protect against capsular fornix aspiration, consecutive zonular dialysis extension, irrigation fluid flow behind the capsule, and vitreous herniation into the anterior chamber.^[3] The implantation of such devices in a deformed capsular bag, usually smaller than normal, is possible due to its mechanical properties. Laboratory studies demonstrate that a continuous-tear circular capsulorhexis can increase 53%–78% in its edge length when distended.^[18]

Gurler et al. performed phacoemulsification in 18 eyes of 15 young adults with isolated lens coloboma, and implanted standard CTR before IOL in cases of defect <120° and Cionni-modified single eyelet CTR in cases with more than 120°, achieving significant visual improvement by this method.^[5] Dhingra et al. performed phacoemulsification in three eyes of two patients with isolated lens coloboma extending more than 120° with implantation of a combination of CTR and capsular tension segment, with significant improvement of visual quality and no intraoperative complications.^[19] Mizuno et al. performed phacoemulsification in two eyes of the same patient and reported that the use of CTR in the second eye facilitated lens rotation and IOL implantation in the capsular bag.^[14]

Conclusion

Considering the ocular morphogenesis and the definition of coloboma, we believe that the ideal denomination for the congenital malformation traditionally known as isolated lens coloboma would be “focal zonular dysgenesis.” To accomplish stabilization and centration of the IOL, our surgical experience in these rare cases associated with the literature results indicates that the best results are achieved using a standard CTR in defects of <120° and Cionni-modified CTR when it is >120°. Better surgical planning can be achieved with an accurate definition of the diagnosis, contemplating the ocular morphogenesis and pathophysiology of this lens abnormality.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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