Dry eye syndrome occurs in patients with psoriasis due to an obstructive dysfunction of the excretory ducts of the meibomian glands. Although their secretory function is normal, the dysfunction results from epithelial keratinization of the glandular ducts (1,2). The patients experience a feeling of dry eyes, foreign body sensation, blurry vision and photophobia, with symptoms worsening throughout the day (6). This complication may be independent from or may be the result of blepharitis or conjunctivitis. Conversely, this syndrome may be associated with the decrease of the tear film, namely the deficiency of L-arginine, which is observed in patients with psoriasis (15).

Blepharitis is one of the most common ocular manifestations associated with psoriasis. Patients exhibit hyperemia, inflammation and edema at the free margin of the eyelids, with slight scaling, itching and burning sensation (1,6,13). Chronic blepharitis may lead to ectropion of the lower lacrimal point with epiphora, madarosis, trichiasis and loss of lid tissue (5,13) or meibomian gland dysfunction, which is frequently associated with posterior blepharitis.

The treatment of patients with blepharitis includes rigorous hygiene (warm compresses, washing the eyelids and lashes with a gentle shampoo) and application of topical corticosteroids on the eyelids (6). The application of tacrolimus ointments may also be taken into consideration (16). In addition, antibiotic ointment application may be necessary for the treatment of secondary bacterial infections; should such complications occur surgery is performed, including in cases of ectropion, trichiasis and pterygium (13).

Conjunctivitis manifests as hyperemia, possible yellowish-red lesions in the conjunctival area and xerosis that may involve the cornea (1). Patients complain of the feeling of grittiness or foreign bodies in the eyes, pain and conjunctival secretions. In cases with complications, such as trichiasis or symblepharon, patients should be referred to an ophthalmologist (6,13).

Several studies have previously reported that patients with psoriasis may develop cataracts (8,13,14). Lens abnormalities, which are generally considered to be incidental findings, are defined by gradually declining vision, glare around lights, decreased contrast sensitivity and visualization of cloudy lens on routine ophthalmological examination. Ultraviolet (UV) radiation contributes to cataract development, as light in the wavelength range of 300-400 nm is absorbed in the lens and may cause photochemical changes in the lens proteins. It has been hypothesized that treatment with psoralen-UVA may trigger the formation of anterior cataracts, whereas prolonged courses of systemic corticosteroids for psoriasis management may cause posterior subcapsular cataracts (13).

Uveitis is a rare but serious eye complication that occurs in patients with psoriasis, and is the most common cause of blindness in developed countries. Anterior uveitis affects the iris, cornea and ciliary body, intermediate uveitis affects the vitreous body and pars plana, and posterior uveitis affects the retina. Anterior uveitis is more common in patients with psoriasis, and it is usually diagnosed at an early stage. Several studies have reported the occurrence of anterior uveitis in 7-25% of patients with psoriasis (1,17,18). This is a bilateral condition and the symptoms include red, painful eyes with pericorneal congestion, reduction or even loss of visual acuity and photophobia may also occur (1,6,12,19). Previous studies have demonstrated the association between uveitis and different types of psoriasis, but uveitis is more frequent among patients with HLA B27-positive psoriatic arthritis (20); however, the association is not fully understood. Uveitis may also develop in patients with pustular psoriasis (5,12). Uveitis is not only a complication of psoriasis, but also of other immune-mediated diseases. It affects several anatomical structures of the eye, without the involvement of any infectious factors (Table I) (14,21-32). This commonly results in disabling complications, such as cataract, glaucoma, band keratopathy or macular edema (23,25).

Corticosteroids are commonly used to treat uveitis, followed by immunosuppressive treatments. In patients who do not respond to these therapeutic options, therapy with TNFα inhibitors (anti-TNFα) may be considered (1,17,21). Although the majority of studies regarding anti-TNFα treatment have demonstrated promising results in terms of the remission of ocular inflammation, cases of exacerbation or eye damage have also been reported. For example, a case reported in 2015 described the induction of uveitis in a patient with ulcerative colitis treated with infliximab (33). Another study demonstrated that 15/54 patients treated at least once with anti-TNFα developed anterior uveitis following therapy. If the treatment is not effective, two possibilities may be considered: TNFα inhibitors are not well-tolerated and do not achieve an appropriate therapeutic response in ocular damage, or TNFα inhibitors induce uveitis (34). Conversely, a recent article demonstrated the efficacy of certolizumab pegol in cases of refractory uveitis or in patients who do not tolerate infliximab or adalimumab (35).

Psoriasis and uveitis have similar immune etiopathogenetic mechanisms, as a result of immunological disturbances in the Th1 and Th17 lymphocyte populations. T17 cells play a key role in sustaining the inflammatory cascade in psoriasis. Secukinumab was the first IL-17A inhibitor to emerge as one of the preferred biological agents to manage chronic psoriasis in patients with multiple comorbidities, including uveitis (36). Notably, ustekinumab has also demonstrated good results in uveitis (37). The incidence of anterior uveitis during treatment with ixekizumab was described; however, in several cases, patients had a pre-existing history of anterior uveitis and were HLA B27⁺ (38).

Therefore, although biological therapies are increasingly used for the treatment of moderate-to-severe psoriasis, their ocular safety profiles remain unclear and further investigation is required.