...difference in eye size? the difference in eye size is specifically noted when the head its tilted or while looking down or when the cheek goes up while laughing or smiling. here, the eyelid of one eye raises while the other eyelid is normal.

There are many types of ptosis..and just as many causes.

Myasthenia gravis, thyroid eye disease (Graves'/euthyroid Graves), Horner syndromes, ocular nerve dysfunctions/palsies, levator dehiscence (an ocular muscle)...and the list goes on to include ptosis as a symptom of other systemic neurological problems.

Specialists who can diagnose and treat ptosis: Neuro-ophthalmologists and ocular plastic surgeons.

They have testing that they can do, including neuroimaging to look at the muscle size, possible nerve ischemia to rule in or out cranial nerve/facial nerve palsies.

Hope this helps.

When you say eye size, I assume you mean the amount of your eye that you can see between your upper & lower eye lid (?)....if this is the case (this is a ptosis & there are MANY types), then I want to tell you about a number of diseases that can cause this:

Myasthenia gravis (more common in diabetes patients), Myotonic dystrophy, Ocular myopathy are all diseases that commonly cause a type of ptosis called Myogenic ptosis. This is a ptosis that results from an abnormal functioning muscle. You mentioned that the difference in size was larger in some positions of gaze (ex. while looking down). A myogenic ptosis could explain this.

Another very common cause for this difference in size is a class of ptosis called Neurogenic ptosis (has there been a recent stroke, seizure...?). This includes a cranial nerve 3 palsy (or misdirection), and Horner's syndrome. Specifically, it can lead to a condition called "Marcus Gunn jaw winking" syndrome. This would help explain the difference in palpebral fissure size (distance between upper & lower lid) while smiling vs while not smiling. Classically, this condition is easily seen while the patient is eating/chewing.

A Mechanical ptosis can occurs from to edema (swelling) or tumors of the upper lid. If you recently have had eye/lid surgery, you may have an Aponeurotic ptosis.

Aside from a true ptosis, this may be due to something known as dermatochalasis. This is simply when excess skin in the upper lid hangs down. Lastly, if you are asking regarding a child/infant, you'll want to consider a Congenital ptosis.

Sometimes patients will think that their palpebral fissure size is decreasing....while in fact it is not decreasing, but the other eye's palpebral fissure size is increasing. The palpebral fissure size of the other eye can increase for many reasons: drug use, space occupying mass behind the eye pushing it forward, and many other reasons.

Best of Luck! If this condition had an acute onset (you noticed it all of the sudden), then it is my recommendation to go see an eye doctor ASAP.