When starting any contact lens evaluation, a careful examination of the ocular surface is vital. It is this surface where the contact lens resides, and if it is at all compromised, this will greatly affect the success of the fit. This post will briefly review the key structures at play. A practitioner must have a general understanding of the corneal / conjunctival surface, tear film and eyelids.
Careful anterior segment evaluation is crucial prior to initiating any type of contact lens fit. In analyzing the cornea, we must rule out signs of epithelial compromise, inflammation, infection, allergy or dryness. When evaluating the conjunctiva signs of inflammation and dryness can include injection, follicles or papillae. For the most part, these findings do not prohibit contact lens use, but they will require adequate treatment before initiating the fitting process.
When addressing the conjunctiva, one of the most common complications of contact lens wear would be giant papillary conjunctivitis. While these findings are most commonly seen with soft lens use, it can be found with rigid, hybrid and sclera lenses.
The function of the tear film is to lubricate the ocular surface, provide anti-microbial properties as well as deliver nutrients and oxygen to the corneal cells. When referencing contact lenses, an adequate tear film is required to insure adequate vision and comfort.
Practitioners can help promote tear stability by understanding the tear components and where and how to manage them. The meibomian glands are responsible for the lipid layer of the tears and receptive to good lid hygiene and Omega-3 dietary supplements. The lacrimal glands are responsible for the aqueous component of the tears. Production here is influenced by nerve stimulation and a reduction may be secondary to an underlying disease process, trauma or medications. Finally you have the mucin layer which is produced by the goblet cells of the conjunctiva. Coating the cornea, this hydrophobic layer is responsible for allowing an even distribution of the tear layer.
Proper eyelid function allows for protection of the ocular structures as well as a mechanism for adequately distributing the tears across the ocular surface. Lid abnormalities such as entropion or ectropion can complicate the wearing process. Other involuntary lid function such as ptosis or marcus gunn jaw winking syndrome can require specialty fitting techniques such altering diameters and lens designs.
Some practitioners are using scleral contact lenses as a way to treat dry eye secondary to lid abnormalities. Studies continue to show that these types of lenses serve as a protective barrier to an otherwise fragile and exposed cornea.
Making sure the ocular surface can support contact lenses is extremely important. Not only will it increase efficiency of the fitting process, but it will greatly reduce the likelihood of complications down the road. When ocular surface disease is found we need to be able to determine if the patient requires treatment, a specialty lens or if contact lenses are even a possibility at all.