VICIOUS CYCLE

The diagnosis of ocular surface disease (OSD) is often overlooked or underestimated in glaucoma patients, even though recognising and treating the condition can greatly improve both quality of life and adherence to the glaucoma treatment, says Prof Maurizio Rolando, Clinica Oculistica, University of Genoa, Italy.

“We need to be aware of the dynamic nature of the ocular surface which is continuously adapting to environmental, toxic, infective, traumatic and inflammatory conditions that the eye is exposed to,” he told delegates attending the 2013 Congress of the Society of European Ophthalmology.

“We need to think about tear and ocular surface dysfunction in our glaucoma patients and look for clinical signs of OSD, which are not difficult to identify but which must be looked for in the first place.” Dr Rolando said that the association between ocular surface changes and IOP- lowering medications to treat glaucoma has been long established.

“In the 1970s, Dr Pfister showed the deleterious impact of 0.01 per cent benzalkonium chloride (BAK) on the corneal epithelium. After several minutes, large numbers of surface cells were shown to retract from their cell contacts leaving retraction fibrils. Many cell edges peeled up, with the loss of microvilli and rupture of intercellular tight junctions. After three hours of BAK exposure, the second layer cells have also undergone extensive degenerative membrane changes,” he said.

The specific term for such medication- related alterations is “medicamentosa,” noted Prof Rolando. “This is what we are seeing in the ocular surface of these patients, a condition used in or caused by a drug or combination of drugs. We see a toxic response with no underlying immune dysfunction and it is one of the most common disorders seen in the subspecialty of cornea and external diseases,” he said.

Prof Rolando emphasised the importance of staining the ocular surface in order to assess the integrity of the superficial cell layers and to give clues to the diagnosis. “Staining the conjunctiva is essential to determining if patients have OSD or not. Because the main focus is on their glaucoma and reducing their IOP, we may miss problems on the ocular surface and fail to recognise the problems that they have,” he said.

The ocular surface has two main abilities, said Prof Rolando, the first one being to protect the eye and the second to maintain the quality of vision. “The ocular surface is a functional unit that maintains the integrity of the cornea, preserves the quality of the refractive surface of the eye and visual function. It also resists injury and protects the eye against changing bodily and environmental conditions,” he said.

Quality of vision largely depends on the quality of the tear film, said Prof Rolando. “We are all aware of the detrimental effect of dry eye on a patient’s quality of life, because this is a problem that they have to deal with all day, every day. We know that moderate to severe dry eye syndrome can adversely affect a person's ability to perform vision-intensive tasks due to pain and impaired vision. In addition, dry eye disease is associated with increased ocular and corneal higher order aberrations,” he said.

He noted that artificial tear administration significantly improves reliability parameters and visual field indices. Rieger in 1992 was one of the first to report that threshold perimetry improved in dry eye patients after instillation of artificial tears, suggesting that tear film supplements stabilised the tear film and improved the optical quality of the eye.

The ocular surface disease index (OSDI) is a useful measure of the severity of the OSD, and underscores the frequency of the problem in glaucomatous patients under medical treatmentImpaired visual acuity, contrast sensitivity and visual function can have a profound effect on vision-related quality of life.

“Dry eye syndrome significantly decreases quality of life and patients’ ability to perform daily functions. One of the few studies by Nordmann et al. that looked at side effects from glaucoma treatment and quality of life showed that 62 per cent of patients reported more than one adverse effect from their treatment including burning, blurred vision, tearing sensation and itchy eyes,” he said.

This has a direct impact on the efficacy of the glaucoma treatment, said Prof Rolando. “You are not going to have a good adherence if a patient’s quality of life is impacted negatively by their treatment. Adverse effects are the third most common reason for non-compliance and they may well be underestimated in clinical trials,” he said.

The ocular surface is a dynamic system with a self-maintaining visual cycle that responds to changing conditions and stimuli. When the cycle is disturbed, intervention is necessary to prevent a cascade of negative effects such as tear evaporation, epithelial cell damage and inflammation, he said.

For patients with a chronic disease such as glaucoma, switching to preservative-free medications may help to reduce the toxic stress on the ocular surface, said Prof Rolando.

“Switching from BAK-preserved to BAK- free medication has been shown to improve epithelial barrier function. Furthermore, some studies have shown that the deleterious effect of BAK on trabecular meshwork cells may be an under-appreciated concern in patients receiving long-term glaucoma treatment,” he concluded.