title: Osmolarity of prevalent eye drops, side effects, and therapeutic approaches.
abstract: OBJECTIVE
  Little is known about how the osmolarity of ophthalmic formulations affects the ocular surface. Because hyperosmolar eye drops could be therapeutic for treating corneal edema, this article presents an ex vivo model of corneal edema for testing ophthalmic drugs based on their osmolarity. The respective osmolarity of common eye drops found in the German market is also analyzed here.
  
  
  METHODS
  For modeling corneal edema, an Ex Vivo Eye Irritation Test was used to simulate an ocular anterior chamber with a physiological corneal barrier. To induce corneal edema, the anterior chamber was supplied with a hypoosmolar medium (148 mOsm/L) for 24 hours. Preserved and preservative-free 5% sodium chloride (hyperosmolar Omnisorb and Ocusalin 5% UD) were used for 1 hour, on 5 corneas each, to test their efficiency to reduce corneal edema in this model. Corneal thickness was determined by optical coherence tomography. Osmolarity of 87 common eye drops was measured by freezing point osmometry.
  
  
  RESULTS
  Ex vivo, the tested hypoosmolar condition induced corneal edema from 450 μm (±50 μm) at baseline to 851 μm (±94 μm, P < 0.0001). Omnisorb and Ocusalin 5% UD significantly reduced the corneal thickness by 279 μm (±28 μm, P < 0.001) for Omnisorb and 258 μm (±29 μm, P < 0.001) for Ocusalin 5% UD. Forty-three (49%) of the tested products had an osmolarity below and 44 (51%) above the physiological tear osmolarity of 289 mOsm/L. Osmolarity values of less than 200 mOsm/L were found in lubricant drops. The highest osmolarity was detected in Omnisorb (1955 mOsm/L).
  
  
  CONCLUSIONS
  The Ex Vivo Eye Irritation Test has proven to be a reliable novel model of corneal edema for evaluating osmotic eye drops. Osmolarity measurements revealed a wide range from hypotonic to hypertonic formulations for commonly marketed ophthalmic drugs.
authors: *Aachen Centre of Technology Transfer in Ophthalmology (ACTO e.V.), An-Institute, RWTH Aachen University, Aachen, Germany; and †Department of Ophthalmology, RWTH Aachen University, Aachen, Germany.
authors: Ralf M
authors: RM
authors: Dutescu
authors: Claudia
authors: C
authors: Panfil
authors: Norbert
authors: N
authors: Schrage
mesh_terms: D000287:Administration, Topical; D000818:Animals; D002626:Chemistry, Pharmaceutical; D015715:Corneal Edema / Q000139:chemically induced / Q000175:diagnosis / Q000188:drug therapy*; D004195:Disease Models, Animal; D007038:Hypotonic Solutions / Q000009:adverse effects / Q000737:chemistry / Q000627:therapeutic use; D065346:Lubricant Eye Drops / Q000009:adverse effects / Q000737:chemistry / Q000627:therapeutic use; D009924:Organ Culture Techniques; D009994:Osmolar Concentration; D061286:Osmometry; D004364:Pharmaceutical Preparations / Q000737:chemistry*; D011310:Preservatives, Pharmaceutical / Q000009:adverse effects / Q000737:chemistry / Q000627:therapeutic use; D011817:Rabbits; D012462:Saline Solution, Hypertonic / Q000009:adverse effects / Q000737:chemistry / Q000627:therapeutic use; D041623:Tomography, Optical Coherence
chemical_list: D007038:Hypotonic Solutions; D065346:Lubricant Eye Drops; D004364:Pharmaceutical Preparations; D011310:Preservatives, Pharmaceutical; D012462:Saline Solution, Hypertonic