How do you manage dry eye syndrome due to lacrimal or meiobian gland dysfunction after external beam radiotherapy?

I have also found autologous serum (AS) or platelet-rich plasma (PRP) eye drops/tears to be extremely useful (provided by an ophthalmologist). Dry eye can also be exacerbated by graft vs. host disease, which I have anecdotally seen worsened within radiation fields and is characterized by a lasting mottled, hyperpigmented skin appearance. AS has worked wonders for a patient of mine for which all other approaches were ineffective.

Although we often contour the lacrimal glands as the avoidance structure during treatment planning, it is important to note that many ophthalmologists believe that the lacrimal gland function is primarily for foreign body and emotional tear production, which requires a large bolus of tears. It may be that the minor lacrimal glands are more critical for baseline eye lubrication. This is analogous to the parotid/submandibular/minor salivary glands within the head and neck, where again the largest gland is actually most critical for bolus needs and the smaller glands are the primary driver of baseline lubrication (and probably quality of life). The meibomian glands are located at the edges of the eyelids where they come together. Avoidance of them, usually using the lens dose as a surrogate, can be helpful through either planning geometry or when appropriate the use of higher beam energies and/or cutting out holes over the eyes in the mask to limit a mini-bolus effect of superficial dose deposition. Superficial dose deposition is inaccurately modeled by most dosimetric software and so I would still consider these "interventions" even if the dosimetry suggests no significant difference.

Lastly, I think worth noting that tears are not just saline. They are complex three-layer biofilm that is probably more complex than we fully appreciate. There is the innermost mucin layer that helps tears stick to the eye, a middle aqueous layer, and, then an outermost lipid layer. The lipid component of tears, produced by the meibomian glands is incredibly important for keeping moisture in the eye. I have seen varying estimates, with some ophthalmologists quoting up to 20 fold faster tear evaporation in the absence of lipid. As you can imagine - this means that adding saline drops without a lipid-based product will not be particularly effective no matter how many times a day you use it. As noted by others, I think the late incidence of dry is likely highly underestimated by radiation oncologists due to our short follow-up, and referral to an ophthalmologist is highly recommended for anyone with concerns for late effects of radiation.

Radiotherapy can cause a variety of deleterious effects on the eye and ophthalmic adnexa. Attempting to prevent these with careful radiotherapy planning and delivery is important. 

Dry eye can begin to occur with acute radiotherapy-associated inflammation and can persist long after this as a late effect of treatment. For most patients, I recommend topical gels or ointments, and these are often required on a long-term basis. 

For patients who do not derive relief from topical medicines, I typically collaborate with an ophthalmologist who has expertise in cancer, radiotherapy, or dry eye syndrome. A variety of medical and surgical interventions can be considered. 

For additional background and possible management strategies, please see:

https://eyewiki.org/Periorbital_Complications_of_Radiation_Therapy