Morgagnian cataract with congenital complete aniridia with congenital lenticular coloboma: A rare association

INTRODUCTION

Aniridia is a genetic eye disease causing partial or complete absence of the iris. Congenital aniridia is an infrequent disorder with an incidence between 1:40,000 and 1:100,000. Aniridia can be unilateral or bilateral in occurrence, and many forms can cause visual impairment that ranges from mild to severe. Besides the absence of the iris, aniridia often presents with other ocular conditions, such as congenital cataracts, glaucoma and nystagmus.^[1] It is mostly associated with the mutations of PAX6, an important gene involved in ocular development.^[2]

Aniridia, in some cases, is seen in conjunction with other syndromes, such as the Wilms tumor, aniridia, genitourinary anomalies and retardation (WAGR) syndrome or other ocular conditions (including megalocornea, lenticular coloboma, or glaucoma).^[3] Although aniridia as a condition cannot be treated, the symptoms can often be alleviated and further loss of vision prevented by managing the condition with treatment options including surgery for cataract or glaucoma, treatment with corrective lenses and continued monitoring.^[4] This case report aims to present an updated overview of congenital aniridia, with the goal of enhancing the clinical management of this ocular condition.

CASE REPORT

A 31-year-old male laborer attended the ophthalmology outpatient department with a history of progressive diminution of vision in both eyes since childhood. The patient described a slow, painless diminution of vision in the right eye with mild ocular pain, redness and photophobia. Due to socioeconomic constraints, he never sought medical help for his vision impairment. The past medical history revealed daily alcohol consumption for 12 years, but no history of ocular trauma or any significant medical conditions. There was no known family history of similar ocular disorders and consanguinity in the family.

At presentation, uncorrected visual acuity was hand movements+ in the right eye and 20/200 in the left eye. Goldmann applanation tonometry revealed corrected high intraocular pressure (IOP) of 28 mmHg in the right eye and normal IOP of 11 mmHg in the left eye. Extraocular movements were full, free and pain-free in all gazes, and there was no nystagmus or squint. Schirmer’s testing was suggestive of very severe dry eye, with findings of <5 mm in both eyes.

Examination with slit lamp showed bilateral mild corneal haze with 360° vascular pannus more than 1 mm (mild limbal insufficiency) according to aniridia-associated keratopathy classification (López-Garcíac et al., 2006)^[5] with subepithelial fibrosis [Table 1]. The right eye showed peripheral conjunctivalisation of the cornea all around, measuring 360° suggesting limbal stem cell deficiency, with significant Descemet membrane at the nasal limbus in the 12–6 O’clock position. There was a white intumescent cataract with sunken nucleus inferiorly, with a shallow anterior chamber of the right eye, while that of the left eye was normal. A 2–3 mm rudimentary iris stump is present circumferentially in both eyes, confirming the diagnosis of bilateral complete aniridia. Multiple anterior capsule calcifications were observed in the right eye, in addition to white morgagnian cataract, and inferior lenticular coloboma [Figure 1a]. There was complete aniridia with congenital cataract (posterior subcapsular cataract) in the left eye without lenticular coloboma. Von Herrick revealed grade 2 in the right eye and grade 3 in the left eye. Gonioscopy showed open angles with increased pigmentation of the trabecular meshwork and few iris processes and rudimentary hypoplastic iris tissue in both eyes. On fundus examination, the right eye showed a glow through the lenticular colobomatous area, while the left eye had a hazy view with only a tilted disc and foveal reflex with no retinochoroidal coloboma. B-scan of the right eye is grossly within normal limits. On the intraocular lens (IOL) master, the white-to-white corneal diameter was 15.3 mm and 14.3 mm in the right and left eye, respectively, in agreement with the diagnosis of megalocornea. Anterior chamber depth (ACD) of the right eye was 1.71 mm, and the left eye was 2.43 mm. Abdomen ultrasonography to rule out Wilms’ tumor and/or genitourinary anomalies was performed and showed only grade 1 fatty liver due to chronic alcohol consumption. Ear, nose and throat assessment was done to rule out auditory dysfunction. A psychiatric assessment was performed to rule out central nervous system involvement. Final diagnosis of congenital morgagnian cataract with megalocornea, limbal stem cell deficiency, aniridia, and inferior lenticular coloboma in the right eye and congenital cataract with megalocornea, aniridia, with limbal stem cell deficiency in the left eye was made [Table 2].

Pre-operative mannitol 200 mL (intravenous) was given over 30 min under cardiac monitoring. The right eye was operated on under local anesthesia using a small incision cataract surgery (temporal approach) for cataract extraction with aniridia IOL with an optic diameter of 5.95 mm, length 12.75 mm, was implanted after informed consent. The Scleral tunnel was closed with 10-0 nylon box sutures. The surgery was successful, and postoperatively, visual acuity in the right eye was improved to 20/40 [Figure 1b].

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Figure 1:

(a) Pre-operative image of the right eye which shows complete aniridia with morgagnian cataract with lenticular coloboma inferiorly. (arrow) (b) Post-operative image which shows aniridia intraocular lens (arrow).

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DISCUSSION

Congenital aniridia is a complex, pan-ocular disease primarily due to heterozygous mutations in the PAX6 gene, which is essential for the developmental processes in the early eye. While the classical note is the complete or partial acquired loss of the iris, individuals with aniridia often present with a spectrum of secondary ocular anomalies, such as congenital cataract, foveal hypoplasia, glaucoma and progressive aniridia-associated keratopathy (AAK).^[5,6] The complex phenotype of these anomalies is largely explained by PAX6 haploinsufficiency, which impairs the regulation of multiple downstream targets required during ocular morphogenesis.^[7]

Our case illustrates a few challenges that are not uncommon in the management of such cases. First of all, this patient had AAK and associated dry eye. He was prescribed preservative-free lubricants. AAK is often worse after surgery that involves excessive manipulation of the limbus while implanting an aniridia IOL. Secondarily, the patient had morgagnian (fluid-filled with small nucleus) cataract with zonular weakness and abnormalities of the anterior segment, megalocornea, and shallow ACD. The lack of zonules in the inferior segment from the 5 to 7 O’clock position and fluid-filled cataract made the capsulorhexis intraoperatively challenging. To avoid intraocular turbulence and to protect the corneal endothelium, a slow infusion technique was performed. The biggest challenge faced was capsulorhexis due to liquified cortex, making it difficult to stabilise. Intraocular forceps were used to complete capsulorhexis successfully. This finding highlights the target zonular weakness that underpins aniridia as syndromic PAX6 loss-of-function mutations lead to generalised developmental deficiencies.^[8]

Congenital aniridia is also associated with several other anterior segment dysgenesis syndromes, such as aniridiaankyloblepharon ectodermal dysplasia syndrome, which complicates the surgical management.^[9] In syndromic cases, the lack of zonules not only predisposes the lens to subluxation; it also requires mindful modifications in the standard cataract surgery technique. The slow infusion technique is essential to decrease intraocular turbulence and preserve zonular integrity. Intraocular forceps, such as those used in our case, gave added control to the process of making the capsulorhexis, which is critical in the presence of zonular dialysis.^[10]

Moreover, the diversity in phenotypic expression (from iris hypoplasia to severe corneal and lenticular defects) is attributed to the different roles of the PAX6 protein in ocular development, as supported by the literature. PAX6 is also known to play a role in differentiation and maintenance in multiple ocular tissues, such as the corneal epithelium, lens and retina. Interruption of these pathways results in a cascade of developmental abnormalities that is exacerbated by secondary sequelae, like in AAK, in which progressive corneal opacification contributes to disintegrating visual acuity.^[6,7]

Key insights into the mechanisms of aniridia have come from animal models, especially a number of different Pax6-mutant mice (broadly termed ‘Sey’ mice). These models recapitulate the human phenotype and highlight the role of PAX6 dosage in normal eye formation. For example, studies using these models indicate that decreased PAX6 expression leads to not just iris malformation but a spectrum of lens and corneal structural abnormalities that corroborate our intraoperative observations of zonular deficiency and capsular difficulties.^[8] Complete anterior segment assessment in terms of the degree of zonular compromise and other concomitant pathologies is important for pre-operative planning. If significant zonular weakness is detected, adjunctive devices, including capsular tension rings or scleral-fixated intraocular lenses, may be used to achieve long-term lens stability and enhance postoperative visual results.^[10]

CONCLUSION

This case describes multiple anomalies that posed considerable surgical challenges. The presence of AAK necessitates lifelong, multidisciplinary management. Ongoing monitoring and patient education are crucial for preserving ocular surface integrity and maintaining visual function in individuals with aniridia.