Abnormal lens shape on CT in a patient with Aniridia

Reduction of lens size in PAX6-related aniridia

Heterozygous mutation of PAX6 in humans leads to congenital aniridia (OMIM 106210) which is typified by congenital iris and foveal defects, and later onset glaucoma, aniridic keratopathy, and cataract. Mice heterozygous for Pax6 mutations phenocopy many aspects of aniridia including the iris defects, keratopathy and cataract, although Pax6 mutant mice have small lenses, a phenotype which is not typically reported in human aniridia, perhaps due to difficulties in measuring lens diameter during typical ophthalmic examinations as the lens periphery is shielded by the iris. In order to overcome this, records of patients diagnosed with congenital aniridia between April 2015 and May 2021 at the Necker-Enfants Malades Hospital, and genetically confirmed with a disease-causing PAX6 variant, were retrospectively reviewed for those with normal axial length whose iris defects allowed visualization of the lens margins and corneal diameter to allow calculation of a lens/corneal diameter ratio. This value was compared with values obtained from a cohort of patients with Sjödell grade IV oculocutaneous albinism type 1 (OCA1; OMIM 203100) which allowed visualization of the lens periphery via iris transillumination. This analysis revealed that patients with congenital aniridia had a significantly lower lens/corneal ratio when compared to those with albinism, suggesting that humans haploinsufficient for PAX6, like mice, rats, frogs, and zebrafish, exhibit reductions in lens size.

Crystalline lens alterations in congenital aniridia

Congenital aniridia is a rare genetic disease associated with mutations in the PAX6 gene. Changes in the lens in aniridia can be alterations of size and shape, of position - which generally reveal zonular weakness and determines subluxation of the lens - and mainly changes in transparency, cataracts, with variable morphology of polar, cortical, subcapsular, lamellar, and more rarely, nuclear cataract. Visual acuity and quality of vision in patients with congenital aniridia complicated by cataracts can be improved by carefully planned surgery, when lack of media transparency justifies surgical indication. Most patients have some improvement in visual acuity and quality of retinal image. Cataract surgery with aniridia is complicated by pathological changes due to the underlying cause of the aniridia. Challenges include corneal opacification, friable capsule and, above all, iris and pupil reconstruction. It can also determine late complications, such as secondary glaucoma or deterioration of pre-existent glaucoma, and corneal endothelial decompensation. After crystalline lens surgery in these patients, either by cataract or dislocation, for visual rehabilitation there are various techniques such as keratopigmentation, prosthetic iris devices or Morcher intraocular lenses with a black diaphragm. An appropriate individualised surgical plan should be selected depending on patient and surgical experience, in order to minimise complications and give the best chance of postoperative success.

Crystalline lens alterations in congenital aniridia

Congenital aniridia is a rare genetic disease associated with mutations in the PAX6 gene. Changes in the lens in aniridia can be alterations of size and shape, of position - which generally reveal zonular weakness and determines subluxation of the lens - and mainly changes in transparency, cataracts, with variable morphology of polar, cortical, subcapsular, lamellar, and more rarely, nuclear cataract. Visual acuity and quality of vision in patients with congenital aniridia complicated by cataracts can be improved by carefully planned surgery, when lack of media transparency justifies surgical indication. Most patients have some improvement in visual acuity and quality of retinal image. Cataract surgery with aniridia is complicated by pathological changes due to the underlying cause of the aniridia. Challenges include corneal opacification, friable capsule and, above all, iris and pupil reconstruction. It can also determine late complications, such as secondary glaucoma or deterioration of pre-existent glaucoma, and corneal endothelial decompensation. After crystalline lens surgery in these patients, either by cataract or dislocation, for visual rehabilitation there are various techniques such as keratopigmentation, prosthetic iris devices or Morcher intraocular lenses with a black diaphragm. An appropriate individualised surgical plan should be selected depending on patient and surgical experience, in order to minimise complications and give the best chance of postoperative success.

Morphometric analysis of the lens in human aniridia and mouse Small eye

Congenital aniridia is caused by heterozygous mutations in the PAX6 gene. In this disease, congenital iris and foveal hypoplasia is associated with juvenile onset cataract, glaucoma, and corneal keratopathy. In rodents, Pax6 mutations result in a congenital reduction in ocular size that is not typically described in human aniridia. Here, the ocular morphometry of aniridia patients is compared with the lens phenotype of Pax6^+/tm1/Pgr mice to reveal whether there are species differences in Pax6 regulation of lens development and homeostasis. Ultrasound biometry (UBM) revealed that eleven percent of aniridia patients exhibited mild microphthalmia while the anterior chamber depth of aniridic eyes was significantly reduced from 6 months of age onward. Although aniridic lens thickness was normal from birth, it was significantly decreased in aniridic lenses older than 30. Notably, 86% of aniridic lenses exhibited cataractous changes in this cohort. In addition, a significant proportion of aniridia patients develop lens subluxation as they age associated with reduced lens diameter as measured by anterior segment optical coherence tomography (AS-OCT). Analysis of young adult Pax6^+/tm1/Pgr mouse lenses by micro-computed tomography (microCT), bright field and dark field imaging revealed that they are reduced in size but did not exhibit overt cataracts at this age. Overall, this study reveals that congenital microphthalmia as assessed by axial length, or microphakia, as assessed by lens thickness, are not typical in human aniridia, although these are primary manifestations of Pax6 mutations in mice, suggesting that PAX6 regulates some aspects of lens development differently between these species.