4.3 .- Restoration of the lipid layer. The lipid layer is the one that has been more relevant in a case of dry eye. We know that in most cases the lipids are of poor quality and deficient, so they cannot perform their function, lubricate the ocular surface or slow the evaporation rate of the tear film. The meibomian glands are clogged and atrophied, which reduces the secretion of lipids and alters its quality. They are “stale” lipids, which are not distributed well enough to generate the outer layer of the tear film. Also, they have a low pH, acid, which irritates the eye surface even more.
To improve the lipid layer, we must act on the meibomian glands and the eyelid margin, as we noticed in the previous section, and if we want to supplement the treatment, we can add some eyedrops new generation, that attempts to emulate the lipid layer.
As we see, the stability of the tear film is a key point being confusing when planning treatment at the same time. Faced with the simple administration of drops, artificial tears, which try to emulate and tear supply deficits and restore stability of the tear film, we propose to treat the causes of instability, especially with regard to the lipid layer, opening the orifice of the meibomian gland and probing the internal duct, restoring lipid secretion and leaving the artificial tears only as an aid to treat dry eye. We also know that artificial tears are not free of secondary effects, even now that most of them are hasve no preservatives. The excessive use of artificial tears can have a toxic effect on the ocular surface.
The improvement of the lipid layer also depends on the level and quality of lipids, on the metabolism in the meibomian glands, something related to diet, (to be precise, to the balance of saturated and unsaturated fats), as stated above in paragraph 3 on therapeutic measures to improve meibomian gland and eyelid margin.
5 .- State of the tissues of the ocular surface. Osmolarity and inflammation.
The direct action of the air on the ocular surface is responsible of cells damage in the cornea and conjunctiva, a phenomenon that will be aggravated by tear hyperosmolarity and an inflammatory response to this aggression.
So far, not much importance has been given to this fact; when the tissue damage was evident with vital dyes, which is basically known as keratitis, a treatment that consists of the prescription of more drops, more viscous artificial tears or contact lenses to protect the cornea. Today the situation has totally changed, both in approach and treatment.
As the tissue damage is the final result of the instability of the tear film, this damaged tissue is responsible for the discomfort felt by the patient and it`s essential to focus the treatment correctly to solve the problem as soon as possible. We must focus our attention on: (1) cell damage, especially in the corneal epithelium, (2) osmolarity of the tear and (3) the presence of inflammatory mediators in tears.
We have pointed out previously the growing importance of hyperosmolarity and especially inflammation, anf that is why the treatment should be focused on the administration of drops that reduce osmolarity, hypoosmolar tears and antiinflammatory drugs. We are aware that this is a controversial issue; there are still many ophthalmologists who occur to be reluctant to the administration of anti-inflammatory drugs. However, we know that in the active phase of dry eye, especially when associated with other diseases with a clear inflammatory component, we must administer these drugs. The good news is that we have a test that measures inflammation so we can adjust the type, intensity of anti-inflammatory and time management, to be able to monitor changes in the concentration of inflammatory mediators, such as metalloproteinase 9 (InflammaDry Detector RPS ®).
It is suitable to administer anti-inflammatory indiscriminately, especially steroidal derivatives, but we know that in the phases of inflammatory activity the cells aggression on the ocular surface is improved and, as a result, the disease progresses rapidly and patient feel more subjective discomfort. For this reason we need the administration of anti-inflammatory drugs to be controlled. In other wordws, we have to choose the most appropriate in each case, adjusting the dose and time of administration.
To help and improve the damaged cells of the ocular surface, we manage substances that have a high regenerative power, as serum and blood plasma derivate. This is not new in medicine: in other specialties, such substance contributes as mediator of cell growth and natural anti-inflammatory effect and, in our case, it helps to soften dry eye. In more advanced cases, when there are corneal ulcers with low response to conventional treatments, new drugs like Cacicol ® (heparan sulfate) have been proven to be effective, reducing the inflammatory reaction of the ulcerated area and helping to regenerate the corneal matrix.
Along with these measures, we could include other drugs such as derivatives of vitamin A, which try to help tissue regeneration even though their benefits are not entirely proven. Recently, many other drugs with molecules that also look for this regenerative effect have been discovered. However, time is needed to verify its effectiveness as a positive alternative to autologous serum and plasma derivatives, more difficult to obtain and manage.
In severe cases, when there is a significant loss of cells in the corneal epithelium and keratitis or corneal ulcers, it is necessary to protect this area and this is why we have special contact lenses acting as a patch, so there is no need to occlude the eye or tarsorrhaphy. Silicone hydrogel with high Dk can enhance the strong subjective complaints that these patients suffer.