Yesterday’s post about training general neurologists to recognize PSP early in the course elicited a reader comment about one patient whose first symptom of PSP was dry eyes.  The diagnosis of PSP remained elusive through multiple years and multiple doctors.  So, a word about that symptom seems in order.

Dry eyes are common in the general population, usually as a result of insufficient tear production, but in PSP the problem is too little blinking – about 20 percent of the normal frequency for age.  This causes inflammation of the conjunctiva (the very thin, transparent layer covering the cornea, the sclera and the inside of the eyelid) and a sensation of dryness or itchiness.  Part of the eye’s reaction is to increase the production of the watery component of tears, but that doesn’t help the loss of the oily component, which comes from a different set of glands. 

Often, the eyes’ reactions also include a reflexive increase in blinking when awake.  This is helpful, but during sleep the lids may remain open because of the basic eyelid dysfunction of PSP.  The resulting drying during the night creates more inflammation than can resolve over a waking day’s-worth of increased blinking.

An ophthalmologist or optometrist evaluating someone for dry eyes may fail to evaluate the blink rate.  Or, if the person has reflexively compensated by increasing the blink rate, the doctor may interpret that as only the normal reaction to inflammation of the conjunctiva. 

So, how can an eye doctor start to suspect early-stage PSP in someone with dry eyes?  Examine the movements of the eyes themselves!  The earliest ocular motor abnormalities of PSP (and here I’m mainly referring to PSP-Richardson’s syndrome, which comprises about half of all PSP) are slow saccades, the “round the houses sign” and square-wave jerks.  None of these require special equipment – just a little book knowledge, a few teaching videos and some practice.  Actual limitation of downward, voluntary eye movement – the “palsy” in the name — arrives a year or two later.  Here’s what those three early signs look like:

1. Slow saccades: A saccade is simply an eye movement, and in PSP they’re slow enough for the doctor to see them in progress, while a normal saccade is too fast – the doctor only sees the starting and ending positions.  In PSP, the slowness is first and worst in the downward direction.
2. The “round the houses sign” is where an attempt to move the eyes downward takes a curved path, as if trying to avoid a direct downward movement.  Probably a more sensitive way to elicit this sign is to ask the patient to perform a diagonal saccade, say from upper right to lower left.  The eyes will first move mostly horizontally and then, once the patient’s visual system realizes that the target isn’t being reached, will force the eyes to move downward to compensate.
3. Square wave jerks are pairs of short, involuntary horizontal eye movements performed by both eyes together up to 20 times per minute.  The eyes first go to the right or left (seemingly randomly) and after a very brief pause, return to the starting point.  They’re especially pronounced when staring at an illuminated target in an otherwise dark room.  They occur in most people with PSP but also in a minority of those with other Parkinsonian disorders and even in a few healthy elderly people. 

So, an ophthalmologist or optometrist seeing a patient with dry eyes should look for these things and if even one of them is present, refer the patient to a neurologist (preferably a movement disorders sub-specialist) to investigate further for PSP.  

I don’t need to remind this readership of the advantages of earlier diagnosis of PSP, even if a cure isn’t yet at hand, but I’ll do so anyway: Access to disease-specific counseling and information; ability to plan one’s financial and living arrangements; avoidance of useless, risky and expensive diagnostic tests and treatments; access to PSP clinical trial enrollment; and the intangible benefit of just knowing what you’re dealing with.