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Wednesday
Apr202011

Herpes Virus and the Eye

Herpes Simplex is a virus broken into 2 categories:  type 1 and type 2.  Easy enough.  Herpes outbreaks or "cycles" occur semi-randomly, but seem to coordinate with periods of other sickness or emotional stress.  The virus itself lives within the host indefinitely as there is no way to eradicate the virus completely, from a systemic standpoint.  So in the realm of eyecare, we treat the local outbreaks of the eye when they occur.  

If your eye doctor tells you you have "herpes of the eye," your official diagnosis is likely Herpes simplex epithelial keratitis.  There are around 48,000 new cases of this per year.  The "epithelium" referenced in the diagnosis is the outermost layer of the cornea (which is the 5 layered clear tissue on the front surface of the eye.)  So this can usually be considered a surface disease and is fairly easy to treat with a topical antiviral called trifluridine.  A newer drug that is now my 1st choice is Zirgan (ganciclovir).  The drug delivery system with Zirgan is superior, being in a gel form. 

Recurrence can be a troubling issue.  Sometimes the patient can have a more severe version of the disease where HSV infects the large central portion of the cornea called the stroma.  Longterm corneal problems such as scarring are more likely in these cases.  

There was a study done around 10 years ago called the Herpes Eye Disease Study that looked at ways to curb recurrence since there always exists the risk of corneal scarring with each subsequent outbreak.  Turns out a low dose oral anti-viral like Zovirax or Valtrex used as maintenance therapy sharply reduced number of outbreaks in the majority of patients.  If you are having bouts of recurrent HSK, definitely discuss this option with your Optometrist.  These low doses tend to be tolerated well with little side effects.  

Valacyclovir (Valtrex) makes a little more sense to me in this regard due to it being a pro drug.  Pro drugs rely on the body to do the metabolism into the more active form.  In effect, getting rid of the "Val" part, which is just an amino acid called Valine that they tack on to make the compound "less active" until the body converts it.  The advantage of this process is to enhance "bioavailability," thereby making the drug available for longer periods of time.  You can usually get by with less frequent dosings as well as lower drug concentration with the Pro form of drugs.  

If you fall into one of these categories of patients who have problems with recurrence rates, this is something to look at.  Most of the time, we can just treat a case of HSK (Herpes Simplex Keratitis)  with a topical antiviral for 2 to 3 weeks and the patient may not have another recurrence for several years.  This meets the standard of care for herpetic surface disease without having to go to an oral.  

Herpes Zoster infections are a different animal and tend to take a higher dosage of antivirals for longer periods.  It lives in the 1st branch of the 5th cranial nerve, or the ophthalmic division of the trigeminal.  

The epithelial disease is the most common and is generally easy to diagnose, though there can be much variation in its staining patterns, making an early diagnosis difficult.  Staining patterns are seen when your doctor puts the ophthalmic dye into your eyes and shines a cobalt blue light at you.  

There are even studies that suggest herpes simplex may have a role in Bell's Palsy (a partial facial paralysis, cranial nerve VII involvement).  

Questions or comments welcome.

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