Keratoconus

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• Down’s syndrome, Ehler’s-Danlos syndrome, Leber’s Congenital Amaurosis and atopy associated with KC but are likely secondary to the eye rubbing associated with these conditions instead of genetic link


• i..e. secondary association in response to environmental or behavioral factors


• only 7 percent of patients report awareness of other family members with this condition


• KC is a complex genetic disease that requires interaction with environmental factors to make a genetically determined predisposition clinically apparent


• hypothesis that KC includes a genetically altered dose-response curve to eye rubbing


• Eye rubbing performed by the purely allergic patients is fairly straightforward. It is in response to allergic symptoms which patients consistently report as “itching.” When asked about eye rubbing, allergic patients are highly aware of their behavior and a typical response might be, “when my eyes itch, I rub them and if they didn’t itch, I wouldn’t rub them.”


• KC patients are very different in this regard. While they may have allergies and their symptoms can certainly overlap with allergic complaints, their observations often include comments not typically associated with allergies. The motivation behind their eye rubbing may include itching as a complaint, but unlike the allergic patient, they often report a number of other reasons such as, “burning” or “it just feels good” or commonly, “I need relief.” KC patients also describe motivating factors for eye rubbing that are never offered by the purely allergic patient, such as, “It helps me see better.” (temporary alteration in surface topography or more likely, an improvement in the quantity, quality and distribution of surface lubrication?)


• Allergy vs KC patients: different perceived need to rub, timing, contact method, pressure applied, duration, motion, location over the lid and the derived benefit


• the purely allergic patient, in response to allergic itching, generally begins by using a flat instrument (back of hand, front of hand or palm applied broadly, rubbing back and forth, horizontally over the eyelids generating eyelid movement and pressure and “traction” within the lid itself with only modest pressure transmitted to the cornea. This is often followed by a transition to using the tip of the index finger as allergic rubbing tends to migrate nasally, concentrating point pressure over the caruncle for the follow through and completion of the effort. Added contact pressure is then applied at this stage when the caruncle is being rubbed and a circular component may also be added to the motion after this transition to the caruncle


• The KC patient, on the other hand, has a limited number of favorite techniques, the majority of which begin with a pointed instrument, either a knuckle (middle knuckle more commonly than distal or proximal knuckle or fingertip(s)


• The hallmark of the KC rub is the circular motion of this point-like pressure confined over the cornea, often with pronounced pressure transmitted posteriorly—much more than with the allergic rub (apart from the allergic caruncle rub). The intensity and duration (10 to 180 seconds, up to 300 seconds) are much greater in KC patients, as is the repetitive nature. The perceived benefit and relief reported by the KC patient is different from the relief from itching sought and achieved by the allergic patient. Interviewing these patients “in action,” the KC patient is more likely to elucidate an experience of ecstasy and euphoric rapture during and toward the completion of the rub, wanting to do even more.


• The purely allergic patient describes the process as filling a need, wishing he did not have to do this, and in the end reports more of a “mission accomplished.”


• Allergic patients are highly aware of these episodes and tend to be fairly accurate when reporting their symptoms, as well as the frequency and severity of eye rubbing, in response to these allergic challenges.


• KC patients often under-report eye rubbing when first asked about it, perhaps reflecting a desensitized awareness as this repetitive behavior or habit becomes increasingly incorporated into their daily routine.


• KC patients may also exhibit repetitive and even ritualistic behavioral tendencies compounding the physical need they feel to rub their eye. This can include profound eye rubbing at certain times of the day or associated with specific activities such as immediately after awakening or after removal of their contact lenses.


• It appears directed at a stimulus derived from the cornea or from the interaction between the eyelid and corneal surface in the absence of a contact lens. While eye rubbing facilitates lubrication and the interaction between the eyelid and the corneal surface in the absence of a contact lens, I also wonder if contact lens removal improves oxygenation to corneal nerves that are stretched and stressed from KC but also somewhat hypoxic after contact lens wear.


• This improvement in oxygenation immediately after contact lens removal might initiate a pain signal that responds favorably to eye rubbing—perhaps in the same way that the gate-control theory of pain explains the benefits of acupuncture or therapeutic massage.


• Relative hypoxia from eyelid closure and the need for better surface lubrication are both factors that might also explain why some patients report early morning as another favorite time to rub their eyes.


• Eye rubbing may also be incorporated in behavioral tendencies associated with obsessive compulsive disease (OCD) as some of these patients reveal these tendencies in other activities in their life.


• It is not uncommon for KC patients to report their eye rubbing more accurately when they return for a follow-up visit, noting that it was called to their attention either by the eye doctor raising the question during the first visit or by family, friends or co-workers the patients might survey with regard to their behavior. Another reason for under-reporting this behavior is an embarrassment that some of these patients feel; they may have been chastised growing up or told over the years to stop rubbing their eyes by their peers or by those in authority. For these patients, it is like nail biting, and when asked to demonstrate their eye rubbing technique, they will often blush and remark on the embarrassment this brings.


• If the patient and their family denies history of rubbing, another theory is that there may be a tendency toward putting pressure on or around the more severely affected eye while they sleep at night.


• position was exclusively on the affected side and involved a hand position that placed considerable pressure on the eye itself.


• consistent tendency for patients to sleep on the side that is more severely affected or progressing more rapidly.


• Some of these patients like to sleep with their hand or fist directly against their eyelid and are more likely to hug their pillow in a manner that generates some compression around their eyes


• While some generate substantial pressure—in effect, grinding their eye into the pillow—even the milder forms of pressure can deliver considerable cumulative effect over time.


• Adding further to this is the thermal impact of compressing a pillow against the closed eyelid, reducing the normal dissipation of heat.


• These patients with asymmetric KC are also more likely to develop floppy eyelids to a greater degree on their sleeping side.


• Also patients are more likely to have undiagnosed obstructive sleep apnea (OSA), a condition that may lead to a host of cardiac and pulmonary problems, hypertension, esophageal reflux, weight gain and shortened lifespan.


• Some KC patients develop OSA symptoms prior to acquiring their weight gain, further supporting the need for a heightened sense of awareness among clinicians who may otherwise overlook this condition.


• Referring these patients to a sleep lab for formal study if they report restless sleep, snoring, periodic apnea, daytime restlessness, unexplained hypertension or any of the other symptoms commonly associated with OSA.


• For those patients already diagnosed with OSA, one should be aware that their favorite sleeping position may be altered by their need to wear a CPAP or BiPAP mask, some of which require patients to sleep on their back to maintain an adequate seal.


• link between KC and obesity. These heavier patients were also more likely to demonstrate a floppy eyelid.


• a hypothesis that a subset of KC patients represents a syndrome that includes a floppy eyelid, “floppy” keratoconic cornea, and floppy soft palate leading to OSA is intriguing and worth pursuing as we try to better understand aging and mortality among our KC patients


• this still does not fully account for the observed reduction in disease prevalence with advancing age.


• patients usually point to the moreadvanced eye as their favorite eye to rub prior to PK. After PK; however, patients often switch so that the other eye becomes the favorite eye to rub


• Their need for relief diminishes, further supporting that it is not the conjunctiva or eyelids producing this need to eye rub, in contrast to what we see with allergic patients. Instead, this may be a product of neurotrophism making the dry-eye symptoms of lid wiper epitheliopathy less symptomatic. Alternatively, this may provide added support to the gate-control theory of pain with neurogenic factors originating in the cornea “short-circuited” by vigorous eye rubbing and then dramatically reduced when tissue containing these stretched or altered nerves is eventually removed with PK.


• Do the prominent corneal nerves seen by slit-lamp biomicroscopy anatomically represent either a response or a contribution to the viscious eye rubbing cycle we see clinically?


• The case is strong that eye-rubbing tendencies of KC patients are overall quite distinct from those seen in the purely allergic patient. Interestingly, these same tendencies are seen in a number of patients with post-LASIK keratoectasia.


• Perhaps the best model for KC is a genetic condition that is particularly susceptible and even accelerated by trauma resulting from eye rubbing or mechanical weakening from LASIK surgery?


• The observed association with OSA brings to mind a number of plausible hypotheses, the most intriguing of which would be a syndrome that includes KC, floppy eyelid and OSA.


• Consider the genetically susceptible host with the environmental “second hit” provided as follows: a) eye rubbing or nocturnal eye pressure leading to the “floppy” keratoconic cornea; b) sleeping position and eye rubbing leading to the floppy upper eyelid; and c) the genetically affected soft palate that has a greater propensity for developing OSA due to a greater susceptibility to become “floppy” and obstruct from airway turbulence at lower levels of weight gain.