A wide range of drops is available to treat sore and dry eyes. Alan Nathan explains the differences between them

SORE AND ‘TIRED’ EYES

Redness and mild irritation in the eyes can be caused by activities such as driving and close work, and by environmental pollutants. Several products, based mainly on astringents and vasoconstrictors, are available. The main active constituents are witch hazel and naphazoline.

Witch hazel

Some products contain distilled witch hazel (hamamelis water), which contains flavonoids and tannins and has astringent and anti-inflammatory properties. However, there appears to be no evidence for its efficacy in ophthalmic preparations.

Naphazoline

Naphazoline, a decongestant vasoconstrictor, is included in some ophthalmic preparations to shrink the dilated blood vessels that cause redness. It is a sympathomimetic agent with marked alpha-adrenergic activity, with a rapid and prolonged action when applied topically. It is documented as being effective in constricting conjunctival blood vessels, and in reducing discomfort associated with ocular inflammation.^1,2 It is included with distilled witch hazel in one proprietary product and is the sole active constituent of another.

Long-term use of decongestant eye drops can lead to rebound congestion (hyperaemia), and a paper has been published documenting a large number of cases of conjunctival inflammation following long-term use.³ Purchasers should therefore be advised not to use these products continuously. Decongestants may slightly dilate the pupils, so their use should be avoided by patients with glaucoma. Because of the slight risk that these ophthalmic sympathomimetic decongestants may raise blood pressure and interfere with carbohydrate metabolism and thyroid function, patients with high blood pressure, heart disease, diabetes or hyperthyroidism should consult their doctor before using these products.

DRY EYE

Dry eye (keratoconjunctivitis sicca) is a chronic condition characterised by dryness of the surface of the eye. It is caused by either a deficiency of conjunctival mucus, due to the absence or significant impairment of the mucin-producing goblet cells of the conjunctiva, or by tear deficiency which is often associated with rheumatoid arthritis. Treatment of dry-eye conditions is usually with tear substitutes (‘artificial tears’). Several products are available, taking slightly different approaches to the problem. The main goal of formulation is to prolong the action and reduce the frequency of application required. Compounds used include: hypromellose, carmellose, polyvinyl alcohol (PVA), carbomer 940, sodium hyaluronate, liposome particles and hydrophobic ocular lubricants.

Hypromellose

Hypromellose (hydroxypropyl methylcellulose) is a mixed cellulose ether with viscosity-enhancing properties, which prolongs the persistence of the water in the drops on the surface of the eye. It is most useful for dry eyes caused by tear deficiency (eg, Sjögren’s syndrome associated with rheumatoid arthritis).

Viscosity of hypromellose solutions increases with concentration, and it has been suggested that the 0.3 per cent concentration of the official formulation may be too low.⁴ On the other hand, too high a concentration can lead to blurring and crusting. The optimum range appears to be 0.5–1.0 per cent. Dextran 70 0.1 per cent is included with hypromellose 0.3 per cent in one product as a fluid volume expander. pH also seems to be an important factor in relation to the comfort of the drops in the eye, slightly alkaline formulations being thought preferable; the official preparation has a pH of 8.5.

Carmellose

Carmellose (carboxymethylcellulose) is a polycarboxylmethylether of cellulose with a variety of therapeutic uses. It is used in eye drops, in concentrations of up to 1 per cent, for the management of dry eye.

Polyvinyl alcohol

Polyvinyl alcohol (PVA) is a viscosity enhancer, usually used at a concentration of 1.4 per cent. It also promotes wetting of the ocular surface, and is useful to help spread the water content of the drops over the eye when the mucus layer is deficient and tear film distribution is patchy. Like hypromellose, PVA enhances stability of the tear film without causing ocular irritation or toxicity. Some preparations also contain povidone, which is thought to mimic the action of natural conjunctival mucin.

Carbomer 940

Carbomer 940 is an acrylic acid polymer that is formulated as a liquid gel for the treatment of dry eye. Its claimed advantages include ease of application and prolonged contact with the corneal surface, requiring application only three or four times a day. In one trial, a carbomer 940 gel-based product was found to remain on the cornea for seven times longer than a conventional PVA-based formulation.⁵

Sodium hyaluronate

Hyaluronic acid is a component of the ground substance or tissue cement surrounding cells and is widely distributed in body tissues and intracellular fluids, including the aqueous and vitreous humours of the eye, Hyaluronate eye drops are useful for treating severe dry eye in Sjögren’s syndrome patients.⁶

Liposome particles

The tear film of the eye is composed of mucin, water and lipids; the latter prevent evaporation of the aqueous component and act as a lubricant for the eyelids. In nearly 80 per cent of cases of dry eye the cause is some sort of disturbance in the lipid layer⁷. An eye spray formulation is available that delivers liposomes to the corneal surface, containing phospholipids that replenish and improve the stability of the lipids. The product is sprayed on to closed eyes and liposomes in the spray migrate across the surface of the eyelid, collecting at the edges of the eye. When the eye is opened the lipid mixture moves into the eyes. The product can be used while contact lenses are being worn.

Hydrophobic ocular lubricants

These are sterilised ointments containing liquid and soft paraffins and wool fat or a similar non-lanolin derivative. They mimic the lipid layer of human tear film and are intended mainly for night-time use to protect and lubricate the cornea during sleep.

Overall efficacy of dry eye treatments

A recent review of 51 studies evaluating 18 different brands of artificial tears and their efficacy, found that all formulations of artificial tears provided significant benefit to patients with dysfunctional tear syndrome, but some proved superior to others.⁸

BLEPHARITIS

Blepharitis is inflammation of the margins of the eyelids, often accompanied by crusting. In many cases the cause is unknown but it is sometimes associated with seborrhoea of the scalp. In these cases, treatment of the scalp with an antidandruff shampoo containing pyrithione zinc, selenium sulphide or ketoconazole may resolve the condition. Hydrophobic ocular lubricants can be used to soften crusts.

 

References

1. Swedish GP Allergy Team. Topical levocabastine compared with oral loratadine for the treatment of seasonal allergic rhinoconjunctivitis. Allergy 1994; 49: 611–615.
2. Abelson MB, Paradis A, George MA, et al. Effects of Vasocon-A in the allergen challenge model of acute allergic conjunctivitis. Arch Ophthalmol 1990; 108: 520–524.
3. Soparkar CN, Wilhelmus KR, Koch DD, et al. Acute and chronic conjunctivitis due to over-the-counter ophthalmic decongestants. Arch Ophthalmol 1997; 115: 34–38.
4. Toda I, Shinozaki N, Tsubota K. Hydroxypropyl methylcellulose for the treatment of severe dry eye associated with Sjogren’s syndrome. Cornea 1996; 15: 120–128.
5. Leibowitz HM, Chang RK, Mandell AI. Gel tears. A new medication for the treatment of dry eyes. Ophthalmology 1984; 91: 1199–1204.
6. Aragona P, Di Stefano G, Ferreri F, Spinella R, Stilo A. Sodium hyaluronate eye drops of different osmolarity for the treatment of dry eye in Sjögren's syndrome patients. Br J Ophthalmol. 2002; 86: 879–884.
7. Heiligenhaus A, Koch JM, Kruse FE, Schwarz C, Waubke TN. Diagnosis and differentiation of dry eye disorders. Ophthalmologe 1995;92:6-1.
8. Moshirfar M et al. Artificial tears potpourri: a literature review. Clin Ophthalmol. 2014; 8: 1419–1433.