Table 1.
Definition of terms used in the description of aniridia and related eye malformations
| Term | Working definition |
|---|---|
| Iris | |
| Aniridia | 1. (Clinical sign) Absence of the iris |
| 2. (Disease) Panocular eye malformation | |
| Complete aniridia | Absence of the iris, with no visible iris tissue (distinction is not made depending on whether any remnant is detectable goniscopically) |
| Partial aniridia | Incomplete aniridia with some visible iris rim (e.g., in classical aniridia) or, less commonly, absence of part of the iris (e.g., in Gillespie syndrome; this is a distinct phenotype to classical aniridia consisting of aplasia of the sphincter) |
| Iris hypoplasia | Unlike aniridia, this is a neutral term which does not imply any particular associated condition. In the context of aniridia, used to describe the minor end of the spectrum of hypoplasia of the iris (cf partial to complete aniridia). The mildest sign of this is iris transillumination |
| Congenital mydriasis | Fixed dilated pupils. In Gillespie syndrome this is due to aplasia of the sphincter |
| Iris coloboma | Approximately 6 o’clock defect in the iris resulting from failure of optic fissure closure |
| Iridolenticular strands | Strands of tissue between the iris and the lens, often seen in Gillespie syndrome or anterior segment dysgeneses |
| Corectopia | Displacement of the pupil, which may be misshapen |
| Other anterior segment | |
| Posterior embryotoxon | An abnormality of the iridocorneal angle resulting in an anteriorly displaced Schwalbe’s line. Characteristic of Axenfeld–Rieger syndrome but seen in 15% normal eyes |
| Keratopathy | A general term for corneal pathology. In the context of aniridia, this is progressive opacification of the cornea over many years, related to limbal stem cell failure |
| Congenital corneal opacification | Congenital corneal opacification may result from aniridia and from other developmental anomalies of the anterior segment such as failure of lens separation. Terms such as Peters anomaly and sclerocornea are clinical signs and are not helpful aetiologically. The authors recommend the classification outlined by Nischal (2015) |
| Cataract | Congenital or acquired lens opacity, with the visual prognosis and need for surgery depending on the age of onset, symptoms, morphological type and laterality |
| Posterior segment | |
| Foveal hypoplasia | Failure of the specialisation of the centre of the macula for fine detailed central vision, visible on OCT as an absent or shallow foveal dip. A core feature of aniridia (but not Gillespie syndrome) and ocular albinism |
| Optic nerve hypoplasia | Visible fundoscopically as a small optic disc, classically with a peripapillary halo and altered ring of pigmentation, with reduced vision correlating not with disc size but with papillomacular nerve fibre integrity |
| Optic nerve coloboma | Excavated optic disc anomaly due to defective optic fissure closure and thus deeper inferiorly, which may involve the whole disc and/or coexist with chorioretinal coloboma and microphthalmia |
| Other | |
| Ptosis | Drooping of the upper eyelid |
OCT optical coherence tomography