Megalocornea
Megalocornea is a rare eye condition characterised by an abnormally large cornea. The cornea is the transparent, dome-shaped front surface of the eye that helps to focus incoming light. In individuals with megalocornea, the cornea is larger than the average size, which can lead to visual abnormalities and potential complications.
Presentation and Clinical Features
Megalocornea is typically diagnosed when the horizontal diameter of the cornea exceeds 13 millimeters in infancy or 12 millimeters in adulthood. However, the exact measurement criteria may vary among studies. Individuals with megalocornea often have an otherwise normal eye structure, including the lens and retina.
The most common symptom associated with megalocornea is reduced visual acuity, which can be present from childhood. Some affected individuals may also experience astigmatism, which causes blurred vision due to an irregularly shaped cornea or lens. In some cases, the enlarged cornea can lead to increased intraocular pressure and glaucoma, although this is less common.
Genetics and Inheritance
Megalocornea can have both non-genetic (non-hereditary) and genetic causes. In the non-genetic form, megalocornea can occur as an isolated eye abnormality without any associated medical conditions. It may also be associated with certain connective tissue disorders or metabolic disorders.
In the genetic form of megalocornea, the condition is inherited in an autosomal dominant pattern. This means that an affected individual has a 50% chance of passing the condition on to each of their children. Several genes have been associated with genetic megalocornea, including CHRDL1, KERA, and ADAMTS17. However, the underlying genetic mechanisms and specific gene mutations involved are not yet fully understood.
Diagnosis and Management
Diagnosis of megalocornea is typically made through a comprehensive eye examination, including measurements of corneal diameter and assessment of visual acuity. Additional imaging tests, such as corneal topography or ultrasound, may be used to further evaluate the cornea's size and shape.
Management of megalocornea focuses on addressing visual impairments and preventing complications, such as glaucoma. Corrective lenses, including glasses or contact lenses, may be prescribed to improve visual acuity and correct astigmatism. Regular monitoring of intraocular pressure is important to detect and manage any signs of glaucoma.
In cases where megalocornea is associated with other systemic conditions or abnormalities, a multidisciplinary approach involving various medical specialists may be required to address the specific needs and potential complications.
Research and Future Perspectives
Further research is needed to better understand the underlying causes and genetic mechanisms of megalocornea. Studying the specific genes associated with genetic megalocornea can provide insights into the normal development and function of the cornea. Animal models and cellular studies can contribute to understanding the molecular pathways involved in corneal growth and the impact of gene mutations on corneal development.
Advancements in genetic technologies, such as next-generation sequencing, may facilitate the identification of additional genes and mutations associated with megalocornea. Understanding the genetic basis of megalocornea can lead to improved diagnostic techniques, genetic counseling, and potential future therapeutic approaches.
Collaboration among researchers, ophthalmologists, and geneticists is essential to further unravel the complexities of megalocornea, improve management strategies, and enhance the quality of life for individuals affected by this condition.
References
- Aldahmesh MA, Nowilaty SR, Alkuraya H, et al. Megalocornea associated with zonular weakness and childhood lens-related secondary glaucoma--a distinct phenotype caused by recessive LTBP2 mutations. Mol Vis. 2010;16:2572-2579.
- Abu-Amero KK, Hellani AM, Salih MA, Alorainy IA. Megalocornea associated with multiple skeletal anomalies: a new autosomal recessive syndrome. Ophthalmic Genet. 2005;26(2):71-76.
- Héon E, Mathers WD, Alward WL, et al. Linkage of posterior polymorphous corneal dystrophy to 20q11. Hum Mol Genet. 1995;4(3):485-488.
- Khan AO, Aldahmesh MA, Alkuraya FS. Genetic and genomic analysis of classic cases of anterior megalophthalmos. Ophthalmology. 2011;118(1):85-92.
