*2.1. Materials and Reagents*

We used the same methods as previously described by Müllerts et al. and Hendegran et al. [24,25]. The following 0.005% (*w*/*v*) PF latanoprost products were included: Monoprost® (Laboratoires Théa—France), Latanest® (Esteve—Spain), Gaap Ofteno® (Laboratorios SOPHIA—Mexico), Xalmono® (Rockmed—Belgium) and Xaloptic® Free (Polpharma, Poland)

In brief, human goblet cells from donors were cultured in Roswell Park Memorial Institute (RPMI) media 1640 1x (32404-014; Gibco, Life Technologies, Waltham, MA, USA) with 10% fetal bovine serum (FBS) (10270-106; Gibco, Life Technologies, Waltham, MA, USA) and 1% of the following mentioned solutions: penicillin/streptomycin (15140-122; Gibco, Life Technologies, Waltham, MA, USA), non-essential amino acid (NEAA) solution (M7145; Sigma-Aldrich, St. Louis, MO, USA), 1 M HEPES (15630-080; Gibco, Life Technologies, Waltham, MA, USA), L-glutamine (25030-024; Gibco, Life Technologies, Waltham, MA, USA) and sodium pyruvate (11360-039; Gibco, Life Technologies, Waltham, MA, USA).

When performing LDH and MTT assays, phosphate-buffered saline (PBS) was prepared with 137 mM NaCl, 2.7 mM KCl, 10 mM Na2HPO4, and 1.8 mM KH2PO4 with a pH value of 7.4, adjusted with either 1 M HCl or 1 M NaOH. Then, 1 M EDTA (E5134; Sigma-Aldrich, St. Louis, MO, USA) in PBS, 0.48 mM versene (15040-033; Gibco, Life Technologies, Waltham, MA, USA), and trypsin (T4799; Sigma-Aldrich, St. Louis, MO, USA) were used when trypsinizing the goblet cells. An LDH cytotoxicity detection kit from Takara BIO, Kusatsu Shiga, Japan (MK401) was utilized, and the MTT assay was performed using 12.5 mM thiazolyl blue tetrazolium bromide (M5655; Sigma-Aldrich, St. Louis, MO, USA) in PBS.

For immunohistochemical staining, 4% (*w*/*v*) of paraformaldehyde in PBS (provided by the RegionH pharmacy) was used to fixate the cells. PBS, Triton-X (1001325622; Sigma-Aldrich, St. Louis, MO, USA), bovine serum albumin (ab181831; Sigma-Aldrich, St. Louis, MO, USA), and saponin from Quillaja Bark (1001658552; Sigma-Aldrich, St. Louis, MO, USA) were used for immunohistochemical staining with the primary antibodies, Cytokeratin7 (ab181831; Abcam, Cambridge, UK) and monoclonal anti-human gastric mucin (M5293; Sigma-Aldrich, St. Louis, MO, USA). The secondary antibodies used were Alexa488 (A11034; Gibco, Life Technologies, Waltham, MA, USA), Texas red (T862; Gibco, Life Technologies, Waltham, MA, USA), and DAPI (D3571; Invitrogen, Waltham, MA, USA).

## *2.2. Physicochemical Characterization*

The osmolality and pH values were measured in triplicate for both diluted and undiluted eye drops. The eye drops were diluted at 1:7 (*v*/*v*) in RPMI media. The pH value was measured at room temperature using a calibrated 744 pH meter (Metrohm; Nordic ApS, Herisau, Switzerland), and the freezing point depression (Osmomat 3000; Gonotec, Berlin, Germany) measured the osmolality. The Wilhelmy method was used to detect the surface tension with a force tensiometer, K-100c (Krüss GmbH, Hamburg, Germany), and the Laboratory Desktop software, version 3.2.2.3068 (Laboratory Desktop, Krüss GmbH). The measurements were performed in triplicate with the undiluted products at room temperature and with a standard deviation of less than 0.1 mN/m.

#### *2.3. Human Conjunctival Goblet Cell Cultivation*

With approval from the Danish National Committee on Health Research (H-17007902) and the Norwegian Regional Committees for Medical and Health Research Ethics (REK: 2013/803), the conjunctiva from post-mortem human donors was cultivated to generate primary goblet cell cultures. Conjunctiva pieces were incubated for 14 days at 37 ◦C and 5% CO2. Media was added to the cultures every day for the first three days and, thereafter, was changed every other day. To keep the purified cell cultures, microscopy of the cells was performed before every media change using light microscopy. If any fibroblasts appeared in the cultures, they were removed manually.
