Non-preservative, non-buffered, inhalent saline is required for scleral contact lenses. There is minimal tear exchange when the lens is on the eye. Long-term exposure to preservatives can cause a sensitivity or toxicity to the cornea resulting in redness and irritation. Non-buffered saline contains only 2 ingredient - purified water and sodium chloride (i.e., salt, or NaCL). By comparison, buffered saline has four ingredients - purified water, sodium chloride,, sodium borate and borc acid. The latter two ingredients can often cause irritation.