Diabetes mellitus may induce various kinds of ocular complications, including diabetic retinopathy and cataract. However, dry eye induced by diabetes is very often overlooked.
There are reports showing significantly higher prevalence of dry eye in diabetic patients – from 15.4 per cent in Type 1 diabetic children to 54.3 per cent in Type 2 diabetic adults (see Table 1). Symptoms of dry eye include ocular discomfort, dryness, foreign body sensation, unstable vision, excessive tearing and sensitivity to light.
How Does Diabetes Affect the Tear System?
Diabetes can disrupt tear secretion. Clinical studies demonstrated a reduction of Schirmer test measurement in diabetic patients.3-7 Evidence from animal studies showed histological and functional alterations in the lachrymal gland as the result of direct hyperglycemia related oxidative stress.8
Moreover, damage to the corneal nerves observed in many diabetic patients may block the feedback mechanism that controls the tear system, further reducing tear secretion.9
Diabetic patients should be advised to maintain a high standard of personal hygiene because their eyes are vulnerable to infections
On the other hand, glucose in the skin, mucous membrane and tears may promote the growth of microorganisms in the conjunctiva and eyelid margins of diabetic patients.10-13 Bacteria like Staphylococcus sp. can be found on the conjunctiva and eyelid of more than 80 per cent of diabetic patients, 10,12 making diabetes a risk factor of conjunctivitis and blepharitis.14,15 Inflammation of the conjunctiva and eyelid may then lead to deficiency of mucin and lipid, further destabilizing the tear film (see Diagram 1).
The effect of diabetes on the anterior segment of the eye should not be overlooked. Patients with diabetes have been shown to have lower tear break-up time,3,5 reduced tear production,3-7 a higher level of Rose Bengal staining 5,7 and fluorescein staining,5 a lower level of lactoferrin and tear-specific prealbumin,5 a higher grade of conjunctival metaplasia,4,6 lower goblet cell density4 and reduced corneal sensitivity.12 Moreover, sustained hyperglycemia can disrupt the corneal endothelial fluid pump,16 causing corneal edema.17 Therefore, any signs and symptoms of corneal swelling should also be closely monitored.
Eye care practitioners have a role in managing patients with diabetic dry eye. Here are some guidelines:
1. Assess tear film function of all diabetic patients regularly. This should include Schirmer test, tear-breakup time, corneal staining, meibomian gland function and other tear film function tests.
2. Diabetic patients should be advised to maintain a high standard of personal hygiene because their eyes are vulnerable to infections. Patients should wash their hands frequently and avoid touching their eyes with their hands.
3. Diabetic patients should be advised to undertake a proper lid-cleaning regimen every day. This helps to remove any crusts, scales and bacteria appearing on lid margins:
a. Wet a clean washcloth with warm water and wring it out. Close eyes and place the washcloth over eyelids for 3-5 minutes. This helps loosen scales and crusts.
b. Wet a clean cotton-tipped swab with water. Gently hold upper lid up and rub the swab over the area where the eyelashes grow out of the eyelid.
c. Gently hold the lower lid down and scrub the lower eyelid.
4. Eye drops are always useful. Formulas containing lubricants like PEG-400 can help relieve dryness and irritations significantly. Since the ocular surface of diabetic patients is compromised, patients are advised to use preservative-free unit dose or multi-dose eye drops that contain disappearing preservatives. These preservatives are decomposed when exposed to light and are safe to the eyes.
Table1: Prevalence of dry eye in different diabetic populations
Diabetic Patients and Contact Lenses
It appears that diabetes is a contraindication for contact lens wear due to the alterations in the cornea and tear system. However, since silicone hydrogel lenses are available in the market, hypoxia due to low oxygen permeability can be virtually eliminated, making contact lens wear possible for diabetic patients. Herse suggested five factors to determine whether a diabetic patient is a good candidate for contact lens wear:18
1. Tight control of blood glucose levels
2. Stable refraction
3. No evidence of corneal epithelial erosion
4. Good compliance with an approved cleaning and disinfection regimen
5. Regular aftercare visits
Blood glucose level of diabetic patients in contact lens wear should be closely monitored.
The ultimate goal of contact lens fitting is to preserve the function of corneal epithelium and endothelium in diabetic patients. I would suggest silicone hydrogel contact lenses with higher oxygen transmissibility worn on a daily wear basis if contact lenses are to be prescribed. This ensures that the oxygen supply to the endothelium is not interrupted and hence the risk of corneal edema can be minimised. I would also advise patients to use a hydrogen peroxide cleaning and disinfection, because laboratory studies suggest some multipurpose solutions (MPS’s) can induce significantly higher cell apoptosis and have negative effect on epithelial cells viability.19
However, if patients are using a MPS, make sure that toxicity staining is being assessed in regular aftercare visits. Recent findings suggested that the risk of corneal inflammatory events is three times higher in patients showing toxicity staining.20 Also, strict compliance to contact lens cleaning instructions including rub and rinse should be assured.
Dr. Gunter Wong graduated from the optometry program at the Hong Kong Polytechnic University. He gained his Master of Optometry degree from the University of New South Wales and his PhD from the University of Hong Kong. His research interest is orthokeratology, visual perception and dyslexia. He is currently the training manager of Abbott Medical Optics Inc.