Medicamentosa

[Eli]

Dr. G,
Your remarks about medicamentosa scared me a little bit. Most of us are aware that this condition can be developed by overuse (wherever that threshold is) of drops containing preservatives (Like BAK, etc) but I was unaware that it could happen when using preservative free solutions. I personally use TheraTears (preservative free) and will towards the end of the day probably use one or two drops every hour to help relieve symptoms of dryness. I have only had significant symptoms of dry eye for about 2.5 months now. Could you you please elaborate on your experiences with (preservative free) medicamentosa and also, given your warning about loss of epithelial adhesion, briefly discuss the merits (or lack of-) of drops with high oncotic pressures like Freshkote?

[DrG]

Dear Eli,

If using the Theratears provides you with comfort, then why are you scared? I think you would know if you were over-using them.

Theratears are hypotonic, which means that they reverse the osmolarity gradient in the direction of increased hydration of the epithelium. This is why they recommend saturation dosing, which is the instillation of one-half of a unit dose container into the eye over a 5 minute period. This is not the same as a full container over a one-hour period.

The overuse of hypotonic solutions can be compared to irrigation with water - the ultimate hypotonic eyedrop. The cornea will exhibit fluorescein staining of the epithelium due to sloughing of the surface cells. No artificial tear duplicates the composition of the natural tear film. Instilling too many artificial tears can deplete the natural tear film rather than augmenting it. If hypertonic solutions are recommended for recurrent epithelial erosions, then surely hypotonic solutions should not be over-used in that situation.

Oncotic pressure is just a term for colloid osmotic pressure. I have no comment about the Freshkote eyedrops, formerly known as APL-105. A high oncotic pressure contributes to the overall osmotic gradient. An artificial tear with a high oncotic pressure would behave as if it were hypertonic, which is why Freshkote is recommended for recurrent corneal erosion syndrome by the manufacturer.

The theory behind hypotonic artificial tears is that the pre-ocular tear film of the dry eye patient is concentrated, i.e. hypertonic. The idea is to reverse that situation.

One more thing that needs to be mentioned is that a compromised epithelial layer has lost its barrier function, i.e. it no longer functions as a semi-permeable membrane. Therefore, any hypotonic solution will pour into the epithelium and quickly lead to edema or swelling.