Study Identifies Progressive Corneal Nerve Dysfunction in Congenital Aniridia Patients

Congenital Aniridia: Progressive Dysfunction of Corneal Sensory Nerves Unveiled

A clinical study has revealed that congenital aniridia, a rare genetic disorder, leads to progressive dysfunction of corneal sensory nerves.

The research, conducted by the Ocular Neurobiology Group at the Institute for Neurosciences (IN), indicates that while corneal sensitivity is similar to healthy individuals in childhood, it significantly decreases by adulthood, affecting the eye's protective mechanisms and regenerative capacity.
The findings, published in the journal Cornea, represent a crucial step towards understanding and potentially mitigating the effects of this condition.

Background on Congenital Aniridia

Congenital aniridia is a rare disease often linked to mutations in the PAX6 gene, which is essential for ocular structure development. Patients with the condition frequently experience partial or total absence of the iris, focusing difficulties, and photophobia.

While previous studies had documented reduced nerve density in the corneas of adult aniridia patients, the functional status of these nerves had not been previously analyzed.
The current study uniquely aimed to understand the functionality of the remaining nerves and their implications for the eye.

Study Design and Methodology

The research team, led by Professor Mª Carmen Acosta and part of the Ocular Neurobiology Group headed by Professor Juana Gallar, evaluated a cohort of aniridia patients, encompassing both children and adults, and compared them to individuals without the condition.

To establish a diverse clinical group, the team collaborated with ophthalmologist Nora Szentmáry from Semmelweis University, Hungary, which facilitated patient recruitment and evaluation across different age groups.
Corneal sensitivity was measured using mild mechanical stimuli delivered via controlled air pulses, as well as cold stimuli. Additionally, tear production was assessed under basal conditions and following activation of the lacrimal reflex through CO₂ microstimulation. The i-Onion device, which originated from a patent held by the research group, was utilized for these measurements. The Institute for Neurosciences (IN) is a joint center of Miguel Hernández University of Elche (UMH) and the Spanish National Research Council (CSIC).

Key Findings

The study yielded several observations regarding nerve function in aniridia patients:

In childhood, corneal sensitivity in aniridia patients was found to be comparable to that of healthy individuals. However, a significant decrease in sensitivity was observed in adulthood. Adult patients required stronger stimuli for perception and demonstrated difficulty in distinguishing between different stimulus intensities.

This deterioration was identified as progressive over time, highlighting a worsening condition with age.

While basal tear production in aniridia patients was similar to individuals without the condition, their ability to increase tear secretion in response to a protective stimulus was significantly reduced.

This limitation impacts a primary ocular defense mechanism, as sensory nerve signals are crucial for activating protective responses such as blinking and tear production, leaving the eye more vulnerable.

The study also addressed the trophic function of sensory nerves, which contribute to the maintenance and regeneration of corneal tissue. The research indicated that when innervation decreases or deteriorates, the cornea's capacity for self-repair is compromised.

This can lead to small lesions, a loss of corneal transparency, and persistent pain, potentially affecting vision and overall quality of life for aniridia patients.

Future Implications and Funding

This research is part of a broader ongoing project. The next phase will involve analyzing nerve function in a mouse model with a PAX6 gene mutation to investigate the cellular mechanisms underlying the progressive degeneration of corneal innervation.
This foundational understanding is intended to contribute to the design of more precise future therapeutic strategies aimed at slowing the deterioration observed in aniridia patients and improving their quality of life.

The study received funding from multiple sources, including the Spanish State Research Agency – Spanish Ministry of Science, Innovation and Universities, the European Regional Development Fund (ERDF/European Union), the Generalitat Valenciana, the Dr. Rolf M. Schwiete Foundation, the Hungarian Academy of Sciences, and the National Research, Development and Innovation Office of Hungary.