Phenylephrine test and ptosis surgery
Mr Hering was a German physiologist in the first part of the 20th century, and he wrote about the law of motor correspondence or innervation equality. He gave his name to a special eyelid test called the “Phenylephrine test,” many years later based on his physiological observations of eyelid heights.
He observed that the nervous influence sent by the nerve that lifts the eyelids to carry out eyelid opening is symmetrical for both eyelids. The central motor impulses are made equally between the two upper eyelids which are known as yoke muscles, as they are bound together in their movements, in this case, eyelid elevation. The fixing eye or dominant eye decides the intensity of these impulses. If that eyelid has a ptosis, there are new impulses to the eyelids which try to lift the most ptotic eyelid and are slightly more successful in lifting the apparent non-ptotic eyelid. When stimulating the ptotic eyelid by the Phenylephrine drop, it goes upwards, and the impulses to both yoke muscles reduce so the opposite eyelid falls giving a positive Phenylephrine test and demonstrating that the person, in fact, has a bilateral upper eyelid ptosis, albeit more marked in one lid that the other. It indicates that they would benefit from bilateral upper eyelid surgery.
If at the point that the Phenylephrine test has lifted one eyelid and demonstrated that the other is ptotic, the surgeon can then quickly put a drop into the other eyelid and explain to the person what the eyelids will look like after they have ptosis surgery. That may sound like a complex area, but it is all part of the skills of the oculoplastic surgery in detecting and assessing the ptosis.
It is a great test, and I use it on mild cases of ptosis especially when asymmetrical to demonstrate the bilaterality and show the patient how super the eyelid can look after surgery. The phenylephrine drop is a sympathetic nerve stimulator and hence stimulates the subtle muscle lying BELOW the levator muscle, called Muller’s Muscle. Muller’s contracts and the eyelid lifts up to the standard height, simulating levator surgery.
They take into account all different aspects of measurements, the height of the lid, curve of the lid, height of the skin crease, curve of the skin crease, amount of skin and function and will then advise on surgery.