Comparison of Surface Conjunctival Temperature With Therapeutic Heat Application to External Versus Internal Eyelid Surface
Purpose
To compare the efficiency and variability of the surface conjunctival temperature when applying therapeutic heat on outer versus the inner eyelid surface for the treatment of meibomian gland dysfunction.
Methods
Thermocouples were placed on the inner lid surfaces of lower eyelids of five subjects. Contact heat was applied to the eyelid external surface using a commercially available chemical heat pack. The surface conjunctival temperature of the inner eyelids was recorded continually at 1-second intervals for 12 minutes of heating. The process was repeated with the heat source on the inner eyelid surface. The 12 minutes of recorded external and internal lid surface data was analyzed to determine time to equilibrium temperature, final equilibrium temperature, and final differential temperature between the heat source and the eyelid surface.
Results
The inner eyelid heat source was regulated to 43.5oC. The outer eyelid heat source was more variable and ranged from 450C to 500C. The inner eyelid heater produced a maximum mean inner eyelid temperature of 42.82oC ± 0.35oC. The outer eyelid heater generated a lower and more variable maximum mean inner eyelid temperature of 40.44oC ± 1.52oC. Therapeutic heat applied to the inner eyelid surface is more efficient and less variable the conventional application of heat to the external eyelid surface.
Conclusion
Therapeutic heat applied to the inner eyelid is more efficient and less variable than conventional application of heat to the external eyelid. Lower temperatures can be used when heating meibomian glands from the inner eyelid surface, reducing likelihood of thermal damage or reduced efficacy from intolerance of high temperatures.