Xeroderma pigmentosum (XP) is a rare autosomal recessive disease, first described by Hebra and Kaposi in 1874 [1]. It affects both sexes equally, and it is due to an abnormality in the system of the nucleotide excision repair [1],[2]. Conjunctival injection and palpebral conjunctival melanosis are the most common reported ocular features. Posterior embryotoxon is a corneal abnormality manifested as a thickening of the Schwalbe’s line, and that may appear like a thin gray-white ridge in the inner part of the cornea [2].

To the best of our knowledge, posterior embryotoxon has never been reported among patients with xeroderma pigmentosum.

A 28-year-old man was referred from dermatology department for a routine eye examination. He was diagnosed with xeroderma pigmentosum since his childhood. He also had an iron deficiency anemia. There was no similar case in his family even though first degree consanguinity was reported. Visual complains were absent.

At physical examination, there was a focal ulcerative lesion in the inter-eyebrow area suggesting a basocellular carcinoma which was confirmed by the histological examination.

A systemic examination didn’t reveal any dysmorphic facial features, such as hypertelorism, flat nasal bridge, or hypodontia, and there was no umbilical or other systemic defects.

Eye examination revealed a bilateral euryblepharon in the medial portion of the lower lids and the presence of a pendular nystagmus (Figure 1). Ocular motility and pupillary reflexes were preserved. Best corrected visual acuity was significantly reduced to 20/80 in both eyes while the intraocular pressure, measured by the Goldmann applanation tonometer, was 15 and 16 mmHg in the right and the left eye, respectively. Slit lamp examination revealed the presence of a temporal posterior embryotoxon, from 2 to 4 clock hours in both eyes (Figure 2). While testing ocular surface dryness, break-up time test (BUT) was found abnormally below 10 seconds.

Furthermore, there was no corneal abnormality and the architecture of the iris was normal in both eyes, without any defect, polycoria, corectopia, or coloboma. The lens in both eyes didn’t appear dislocated or subluxed, and there was no sign of cataract. Indirect ophthalmoscopy and biomicroscopy showed that the cup-to-disc ratio was 0.3 in both eyes. Macula’s examination revealed a bilateral foveal hypoplasia. A gonioscopy examination was done and showed an open angle with a prominent and anterior displaced Schwalbe’s line. There was no iridocorneal adhesion, or any other sign of dysgenesis of the angular structure.

An optical coherence tomography (OCT) scan was performed and confirmed a foveal hypoplasia grade 2, characterized by the absence of foveal pit. The patient was treated by artificial tears, advised to wear adapted ophthalmic ultraviolet radiation (UVR) protection and monitored for intraocular pressure.

Posterior embryotoxon consists of a thin layer of Descemet’s membrane surrounding collagen fibers. It appears as a thick gray-white ridge of Schwalbe’s line, which is anteriorly displaced. Most frequently, it is described in anterior segment dysgenesis, such as in Axenfield–Rieger’s syndrome, where it results from an abnormal development of the neural crest.

It can be encountered in systemic disorders, like in Alagille’s syndrome [2]. Posterior embryotoxon can also be seen as an isolated item. Incidence of posterior embryotoxon varies between studies, with a range from 12% to 32% [2].

When posterior embryotoxon is associated with iris and angle anomalies, it may induce glaucoma. Actually, Shields [3] showed that when posterior embryotoxon is isolated, it may increase the risk of development of glaucoma. To the best of our knowledge, posterior embryotoxon has never been described in xeroderma pigmentosum. The posterior embryotoxon was isolated and was not associated with any sign of glaucoma. It is mandatory to maintain a follow-up to seek the risk of glaucoma development. In fact, the most frequent ocular features in this disease are found to be in the periocular skin or in the ocular surface, and are typically represented by eyelid tumors or atrophy, exposure keratitis, severe dry eye, pterygium, and chronic conjunctival injection [1].

Some corneal changes can also usually be found in xeroderma pigmentosum, such as scarring, stromal edema, scarring, or corneal thinning [4]. In this case report, our patient had an inter-eyebrow basocellular carcinoma as a periocular skin lesion. In 40–45% of the cases [1], patients presenting xeroderma pigmentosum may have at least one ocular abnormality and may cause visual impairment.

Ocular manifestations in xeroderma pigmentosum are, for most, related/linked to photo-exposure. Fundus abnormalities are uncommonly seen in xeroderma pigmentosum, as the posterior segment is normally protected from ultraviolet (UV) rays by the lens and the cornea. However, our patient had a bilateral foveal hypoplasia grade 2. It is usually associated with nystagmus and variable visual acuity loss, like it was the case of our patient. Foveal hypoplasia is mostly bilateral and it is often seen in aniridia, achromatopsia, albinism, or even PAX6 mutation associated diseases [5].

To the best of our knowledge, foveal hypoplasia has never been described among patients presenting xeroderma pigmentosum.

In conclusion, our case report tends to describe the possible association between posterior embryotoxon and xeroderma pigmentosum. The main limitation of our study is due to the lack of genetic testing and counseling after ascertainment of posterior embryotoxon. As this association is rare, further delineation of genotype-phenotype associations may have to be assessed for a better understanding of the pathogenesis of this disease and its manifestations in order to offer patients more individualized care.