Dermatochalasis ("hooding") and ptosis are separate eyelid problems. Blepharoplasty treats excess skin; ptosis repair fixes levator or nerve dysfunction. Because the brain supplies equal innervation to both levator muscles (Hering's law and a central midbrain nucleus), correcting one eyelid can change the appearance or function of the other. Surgeons use MRD1, levator function tests, visual field testing, and temporary maneuvers to plan whether to operate on one or both lids. Insurance coverage requires documentation and varies by payer.
What "hooding" (dermatochalasis) is
As skin and connective tissue loosen with age, excess upper eyelid skin can fold over the eyelid margin. Surgeons call that dermatochalasis (commonly "hooding"). It can be a cosmetic concern and, when severe, interfere with the superior visual field.
Two different problems: excess skin vs true ptosis
Removing excess skin is blepharoplasty. For many people, a conservative upper blepharoplasty restores a smoother lid contour and opens the visual field.
But some patients have true eyelid ptosis - a drooping lid caused by laxity or dysfunction of the levator muscle/aponeurosis, or by nerve injury. Ptosis usually needs a dedicated ptosis repair (levator advancement or Müller muscle procedure, or, in severe cases, a frontalis sling).
Why the brain matters: Hering's law and central control
Eyelid height isn't only local muscle mechanics. The midbrain contains a central nucleus that gives coordinated input to both levator muscles. Because of Hering's law of equal innervation, the nervous system tends to send the same command to both eyelids. When one lid droops, the brain increases signal to lift it - which can make the other lid appear retracted.
That interaction means correcting one lid can reveal or change the apparent position of the other. Good surgeons test for this preoperatively (temporary elevation of one lid or other maneuvers) to identify a "Hering component" and decide whether to treat one or both sides.
How surgeons evaluate patients
Surgeons measure eyelid position with the marginal reflex distance (MRD1) and assess levator function. They also check the visual field - often with automated or manual perimetry - when functional coverage is claimed.
Other useful tests include the phenylephrine test (to predict response of Müller muscle procedures) and temporary eyelid taping to reveal a contralateral Hering effect.
Insurance and medical necessity
Many insurers will cover eyelid surgery when it is functionally necessary, not solely cosmetic. Insurers typically require documentation such as MRD1 measurements and visual field testing. Specific numeric thresholds and policies vary by payer and over time, so check your insurer's criteria before planning surgery.
Choosing a surgeon and what to expect
See an oculoplastic surgeon or an ophthalmologist with eyelid expertise. A measured, staged approach reduces the chance of needing a second operation. Recovery commonly includes swelling and bruising for 1-3 weeks; final contour may take several months.
If prior nerve injury (stroke, facial palsy, cranial nerve III palsy) contributed to ptosis, planning becomes more complex because of altered central control and muscle function. A surgeon experienced with those scenarios will discuss options and likely outcomes.
Bottom line
Excess skin (hooding) and true ptosis are distinct issues that can coexist. Modern evaluation targets the specific problem - blepharoplasty for dermatochalasis, a ptosis repair for levator/nerve-related droop - and takes neural control (Hering's law) into account when deciding whether to operate on one or both eyelids.
- Confirm current insurer thresholds and exact numeric criteria (e.g., MRD1 cutoff, millimeter difference) for coverage of eyelid surgery with major US payers and Medicare local coverage determinations.
- Verify standard clinical MRD1 cutoff values used to define functional ptosis in insurance policies and clinical guidelines.