Since their introduction to the general public in the late 1950s, contact lenses have gained steadily in popularity with advances in lens materials, designs, fitting, and care. Early contacts were made of polymethyl methacrylate (PMMA), a rigid polymer impermeable to the transmission of gases—both the oxygen the cornea consumes as it respires and the carbon dioxide it produces. Moreover, the sensitivity of the eye to lens edges and also to airborne particles meant that many patients could not tolerate their discomfort.
“Soft” lenses made of pliable, water-absorbing polymers became available in 1971 and quickly exceeded hard lenses in popularity. They transmit oxygen relatively well because of their high water content (up to 75 percent in some), and they shape themselves to the cornea, allowing quick adaptation by the eye and increased comfort. Unfortunately, soft lenses, known as hydrogels, are less durable than hard lenses and require greater care and more frequent replacement. With them the eye is more prone to infection and a number of other complications and, while well suited for correcting myopia (nearsightedness), they are often unable to correct astigmatism adequately.
Rigid gas-permeable lenses (RGPs), available since 1979, combine good gas transmissibility and the superior optical properties of rigid materials. However, they suffer from some of the same problems as the older PMMA lenses, including greater sensitivity to foreign particles in the eye and increased risk of lens displacement or loss.
Both hydrogel and RGP lenses available today offer the possibility of extended wear for periods longer than a day. About a third of the hydrogel lenses in use are of this extended-wear variety (Schein, 1990), with a typical wear time of one week.
Nonetheless, all contact lenses, either daily wear or extended wear, must be removed at regular intervals to prevent complications from oxygen deprivation, bacterial infection, and mechanical irritation.
What Causes an Allergic Reaction to Contacts?
Contact lens materials.
There are two main kinds of contact lenses: soft and gas permeable. Soft contact lenses are made of a plastic polymer and contain at least 10% water. They contribute to more eye infections than rigid or gaspermeable contact lenses. Wearers of these lenses are at a greater risk of developing eye infections and corneal ulcers. These conditions can develop quickly — usually within 24 hours of exposure to the offending agent; they can be very serious and, in rare cases, cause blindness.
More is demanded from ophthalmic treatments using contact lenses, which are currently used by over 125 million people around the world. Improving the material of contact lenses (CLs) is a now rapidly evolving discipline. These materials are developing alongside the advances made in related biomaterials for applications such as drug delivery. Contact lens materials are typically based on polymer- or silicone-hydrogel, with additional manufacturing technologies employed to produce the final lens.
Contact lens cleansing systems
Multipurpose contact lens solutions are the dominant disinfection method used by contact lens wearers today.
What Is Contact Lens Intolerance?
Contact lens intolerance is the same as contact lens discomfort (CLD) that is assessed by ophthalmologists in research. Factors causing CLD can be either contact lens-related or environmental. Contact lens-related factors can be associated with:
- material (lubricity, water content),
- design (edge, base curve, asphericity),
- wearing schedule,
- care system (chemical composition, regimen).
It has been estimated that there are currently more than 140 million contact lens wearers worldwide (Nichols JJ, written communication, 2013). It is much more difficult to estimate the number of individuals who have previously worn contact lenses and then abandoned lens wear as a result of CLD. Studies have reported that between 12% and 51% of lens wearers “drop out” of contact lens wear, with CLD remaining the primary reason for discontinuation.
Environmental factors can be subdivided into:
- ocular surface condition (dry eye, tear composition),
- external environment (humidity, wind, temperature),
- occupational factors (computer, light, altitude, and other occupational related changes in the external environment),
- other factors (age, gender, background ocular or systemic diseases, psychiatric and psychological conditions).
Out of these, young age, female gender, tear quality and quantity, seasonal allergies, psychological factors, the use of some medications, room humidity, and wind and blink-rate altering activities are clinically related to CLD.
Signs That You May Be Allergic to Contacts
WHO conducted a large study trying to identify why people stop wearing lenses and what were the symptoms they were complaining about. They found that “dryness” of the eyes was the number one complain, while the eye really does not have receptors or nervous endings that are capable of experience it. The perception of symptoms of contact lens–related discomfort is complex and likely results from interactions across multiple psychophysical channels. Other than dryness, “scratchy” and “watery” sensations have been reported 52% and 30% of the time, respectively, in daily hydroxyethyl methacrylate (HEMA) contact lens wearers. Other symptoms have also been reported. Among a sample of 83 adapted contact lens wearers, blurry vision was a frequent symptom. Scratchiness and irritation were infrequent symptoms, and light sensitivity and eye soreness were seldom experienced. In a large population-based study of dry eye (2500 subjects including some contact lens wearers), blurred vision was found to be the most commonly reported symptom.
It is difficult to tell when the allergy to contacts or cleaning materials start and how it is different from just a discomfort. It is possible that those are just different interpretations of the same process. After all, if you removed the lenses and symptoms went away – here is your answer!
What Can I Do to Avoid Irritation?
Standard daily-wear soft contact lenses should be cleaned daily. Several professional groups that represent optometrists and ophthalmologists recommend rubbing each lens in the palm of the hand with a few drops of solution, even if using a “no rub” product.
The importance of careful eye care with contacts
Contacts and allergies
Giant papillary conjunctivitis (GPC) can occur with any type of contact lenses. The coating on the lens and the contact lens trauma to the conjunctiva are probable factors. Changing the polymer of the contact lens that a patient with GPC wears can decrease the chance of the condition recurring. Also, replacing a soft contact lens at intervals of less than 3 weeks, rather than 4 or more weeks, significantly reduces the chance of developing GPC. GPC can occur with high Dk silicone contact lenses. Two forms of GPC have been reported: a generalized form similar to that seen with conventional soft contact lenses and a localized form in which the papillae are confined to one or two areas of the tarsal conjunctiva, near the lid margin.
Contacts and infections
Improper care of contact lenses can lead to a variety of eye infections including infectious keratitis. Experts in the eye care field agree that estimated rates of microbial keratitis in the contact lens–wearing population has not substantially declined since the first disinfection method using heat, despite the evolution of contact lens disinfection systems.
Risk factors associated with an increased risk for eye infections include inadequate hygiene, noncompliance with schedules for wearing contact lenses or contact lens care systems, and contamination of contact lens materials.
Basic Preventative Steps to Combat Allergies
The modifiable environmental factors should be addressed first. Increasing room humidity, avoiding being in the direction of windy air conditioners, intermittently looking at far objects during computer work, and adjusting the angle of gaze at the computer monitor are simple modifications that can help.
A variety of treatment options exist to control ocular allergy symptoms. Nonpharmacologic options include allergen avoidance and lubrication with saline, and if these fail to be sufficiently effective, symptom relief may be provided by medicinal agents that are either applied topically to the eye or taken orally. Recent evidence suggests that nasal allergy treatments applied topically to the nose may also positively affect ocular allergy symptoms, which raises the interesting possibility that a parasympathetic nasal-ocular neural reflex pathway may be involved in the stimulation of allergic responses in the eye.
The Importance of Proper Contact Lens Care.
Eye Drops for Itchy Eyes.
Ocular antihistamine drops such as olopatadine and epinastine can decrease symptoms in patients with history of allergic conjunctivitis, even in the absence of symptoms, while oral omega-3 fatty acids can decrease dry eye symptoms.
For the patients who remain symptomatic despite the above-mentioned modifications, a trial of changing the lens type to another with a better surface wettability, and more frequent replacement schedule preferably daily disposable can be helpful.
News – a lens delivering medication.
A contact lens (CL) – based drug delivery system for therapeutic delivery of the antihistamine ketotifen was tested in 2 parallel, conjunctival allergen challenge-based trials. This large-scale assessment (n = 244) is the first demonstration of efficacy for CL delivery of a therapeutic for ocular allergy. Results are comparable to direct topical drug delivery and suggest that the lens/ketotifen combination can provide a means of simultaneous vision correction and treatment for CL wearers with ocular allergies.