Transconjunctival lower blepharoplasty does not alter the tear mechanism and/or the eyelid function and therefore it is safe in dry eye patients. Transcutaneous lower blepharoplasty carries more risk of altering the eyelid contour and position which in effect can affect eye closure and worsen dry eyes. See an oculoplastic surgeon for evaluation.
A Schirmer's test measures tear production. However, it is used clinically as an ancillary test. Much more important is your clinical history which is determined by a very careful guided conversation your surgeon should have with you about dry eye symptoms and in the case of Sjogren's syndrome dry mouth and the nature of any systemic treatments you may need to manage this condition. A drug history is also important because many drugs we take also have a bearing on tear production. Specific information is also very important like your ability to tolerate contact lens and any history of refractive surgery. A detailed physical examination is then performed looking at the blink, evidence of lid closure strength, Bell's phenomena which give us an idea of how well protected the corneal surface when the eyes are closed. Using a slit lamp microscope, an instrument only used by ophthalmologists and oculoplastic surgeons, the eyelid margins are assessed for evidence of chronic lid margin inflammation, the quality of the physical tear film is studied. The conjunctiva is then assessed for evidence of chronic inflammation. Finally, the corneal surface is studies for evidence of active dry spots, old scars and thin spots, and microvascular ingrowth that are used to assess the overall heal of the corneal surface. It is my opinion that this assessment needs to be performed by the surgeon him or herself. No one else is really in a position to integrate this information. Simple "clearance" by the ophthalmologist is not sufficient. You need to see a surgeon who has to manage dry eye after eyelid surgery so they truly understand the potential impact of these surgeries. This will be a fellowship trained oculoplastic surgeon. Even the 6 to 8 weeks of swelling associated with transconjunctival blepharoplasty healing can have a profound impact on corneal heal for someone with significant Sjogren's syndrome. For this reason, many individuals in this circumstance are advised not to have blephaorplasty but to consider treatments like under eye fillers as a nonsurgical alternative.