Allergic conjunctivitis: An in-depth guide with practical information

Allergic conjunctivitis is a condition that occurs when the conjunctiva (an almost transparent membrane that covers the white part of the eye, the sclera, and also the eyelids on the inner side) become inflamed as a consequence of an excessive reaction of the immune system (in response to an external agent). Its function is to protect the eyeball from external agents, although it is also involved in forming tear components and the eye's immunological defense.

Going more into scientific concepts, we should mention that allergic conjunctivitis is due to a type I hypersensitivity reaction to a specific antigen.

Allergic Conjunctivitis

It is essential to know that there is not only one type of this condition, but there are several manifestations, each of which will be explained in detail below, as well as its manifestations and treatments.

In most cases, seasonal allergic conjunctivitis (hay fever conjunctivitis) tends to peak in spring, late summer, or early autumn and disappears during the winter months, depending on the life cycle of the plant responsible.

Conjunctivitis: symptoms

Ocular pruritus is the most frequent symptom (particularly intense in the nasal quadrant of the eye), together with conjunctival hyperemia. There may also be foreign body sensations, burning, and tearing. The discharge is watery at first, becoming serous and thicker in chronic forms; the eyelids and conjunctiva are usually involved, with varying degrees of chemosis (gram blister appearance).

The palpebral conjunctiva usually has a pale pink or milky appearance (related to edema); corneal involvement is less frequent, although punctate epithelial keratitis may be found. Unlike other ocular diseases, it is rarely followed by permanent visual impairment.

Conjunctivitis: Causes

Among the most frequent causal agents are tree, grass, and weed pollens that present a botanical periodicity.

It is usually a type 1 hypersensitivity reaction (IgE-mediated) triggered by aeroallergens that bind to mast cells upon binding to their IgE receptors, causing their degranulation with subsequent release of cytokines and other inflammatory mediators.

The reactions produced can be divided into an early phase lasting 20 to 30 minutes, which is related to the specific activation of conjunctival mast cells, causing their degranulation, releasing histamine, proteoglycans, proteases (tryptase, chymase), acid hydrolases and oxidizing enzymes, as well as de novo formation of lipid mediators (prostaglandins and leukotrienes), platelet-activating factor, interleukins (IL4, IL5, IL6, IL8, IL13) and tumor necrosis factor-alpha (TNF-α). After that, this reaction follows a late phase caused by stimulation of epithelial cells and fibroblasts with the release of proinflammatory cytokines and chemokines and characterized by infiltration of inflammatory cells (neutrophils, eosinophils, lymphocytes, and macrophages), with subsequent persistent conjunctival inflammation; unlike other allergic diseases, there is little eosinophilic infiltration in acute forms, which increases as the pathology becomes chronic.

Perennial allergic conjunctivitis (PAC)

Perennial allergic conjunctivitis (PAC) (atopic conjunctivitis, atopic keratoconjunctivitis) is mainly caused by dust mites, animal dander, or other non-seasonal allergens. These allergens, especially in domestic environments, cause symptoms throughout the year.

Symptoms are persistent and may be exacerbated both seasonally (79% of cases) and by non-specific irritants, and there may be some cases associated with occupational exposures, such as in flower growers.

PAC may be more likely to cause chronic inflammation than seasonal due to the prolonged nature of the exposure.

Vernal keratoconjunctivitis (VKC)

On the other hand, vernal keratoconjunctivitis (VKC) is a more severe type of conjunctivitis, more likely allergic in origin. It is common in males between 5 and 20 years of age with a history of eczema, asthma, or seasonal allergies. Vernal keratoconjunctivitis typically recurs each spring and subsides in the fall and winter. Many children outgrow the disease in early adulthood.

This is characterized by a chronic bilateral and recurrent inflammation, whose predominant symptom is usually intense itching, to which are added hyperemia, edema, photophobia, foreign body sensation, lacrimation, and the production of a whitish and fibrous secretion composed of eosinophils, epithelial cells, and Charcot-Leyden crystals. The symptoms are usually exacerbated by exposure to wind, dust, solid lights, or physical exertion with sweating.

This condition mainly has two forms of conjunctival involvement: tarsal and limbar. The first is related to the presence of giant papillae (7-8 mm) that primarily affect the upper tarsal conjunctiva and give it a characteristic cobblestone appearance. In the limbus, Horner-Trantas spots can be found, which are observed as small gelatinous nodules, are typical of the active phase of the disease, usually last from 2 to 7 days, and are caused by the accumulation of eosinophils and epithelial cell detritus.

It should be noted that giant papillae present in the tarsal conjunctiva cause mechanical damage and corneal involvement in 5% of patients; in these cases, micropannus (vascularization of the cornea as a result of repeated inflammation), superficial punctate keratopathy (punctate epithelial denudation usually located in the upper half of the cornea), corneal macroerosions and ulcerations can be observed. In persistent forms, subepithelial fibrosis is generally found, appearing as a linear whitish scar parallel to the lid margin (Arlt's line) and pseudogerontoxon (opacification of the cornea adjacent to the upper limbus).

It is necessary to mention that histopathologically, VKC corresponds to both a type I and type IV hypersensitivity mechanism. Conjunctival biopsy reveals increased basophils, eosinophils, degranulated mast cells, plasma cells, and lymphocytes. Tears show high levels of histamine, tryptase, eotaxin, eosinophil cationic protein, major essential protein, adhesion molecules (VCAM-1), leukotrienes (LTB4, LTC4), IgE and IgG specific for aeroallergens and eosinophils in 90% of cases, supporting both a Th1 and Th2 response.

Although it can be self-diagnosed by signs and symptoms, it is important to treat in time for possible refractive pathologies it might cause in children.

Now, one of the main symptoms is ocular pruritus (itching); that is why we must treat our children immediately to avoid the response that is caused, which is rubbing since it can cause a mild to severe "astigmatism" when performing this act.

On the other hand, not having control over how to treat the symptoms can trigger a thinning of the cornea, which leads to a dreaded "keratoconus" (conical shape of the cornea), producing irregular and diminished vision at an early age.

In case of the appearance of symptoms compatible with allergic conjunctivitis (red eye, tearing, itching, foreign body sensation, mucous secretion, egg white appearance...), it is necessary to visit a specialist for its timely diagnosis and treatment.

Conjunctivitis: Treatment

The initial treatment consists of attenuating the symptoms and periodic control with the specialist.

Let us remember that prevention is the basis of medicine, leading us to avoid serious complications.

  • Over-the-counter topical antihistamines, nonsteroidal anti-inflammatory drugs, mast cell stabilizers, or a combination of these.
  • Topical corticosteroids or cyclosporine for treatment-resistant cases. Sometimes oral antihistamines.
  • Avoiding identified allergens and using cold compresses and artificial tears can reduce the symptoms of allergic conjunctivitis; antigen desensitization is sometimes helpful.
  • Over-the-counter antihistamine eye drops (e.g., ketotifen) may be effective in mild cases. When these drugs are insufficient, prescription antihistamine eye drops (e.g., olopatadine, bepotastine, azelastine, cetirizine), mast cell stabilizers (e.g., nedocromil, cromoglycate), or nonsteroidal anti-inflammatory drugs (e.g., ketorolac) may be used separately or in combination.
  • Topical corticosteroids (e.g., loteprednol eye drops, 0.1% fluorometholone, 0.12-1% prednisolone acetate in drops three times daily) may be helpful in treatment-resistant cases or when rapid relief of symptoms is of interest. Because topical corticosteroids can cause an outbreak of latent ocular herpes simplex virus infections, with a risk of ulceration and perforation and, in prolonged use, glaucoma and cataracts, their administration should be initiated and supervised by an ophthalmologist.
  • Topical cyclosporine drops may be helpful. Corticosteroid ointment or tacrolimus applied to the skin is very effective in treating atopic dermatitis of the eyelids.
  • Oral antihistamines (e.g., fexofenadine, cetirizine, or hydroxyzine) may be helpful, especially when patients experience other allergic symptoms (e.g., rhinorrhea).

Seasonal allergic conjunctivitis does not usually require drug combinations or intermittent topical corticosteroids.

Dr. Glaybeth Lara Hidalgo