Dry eyes can happen when tear production and evaporation are imbalanced and be caused by a combination of different reasons – aging, environmental stress (i.e., UV light, weather), lenses, medications, etc. 
Many patients who undergo eye surgeries, including LASIK or LASEK, cataract surgery, and keratoplasty, can also develop dry eyes, characterized by itching, irritation, burning, and dryness. To relieve these dry eye symptoms, the recommended first-line of treatment is lubricating eye drops. 
With a wide selection of eye drops available in the Canadian market, you and your patients may be unsure of which lubricating eye drop is ideal for post-surgical use. Upon searching, you may have come across phosphate-free eye drops and wonder why phosphate-free drops are recommended.
How phosphate in eye drops may damage the corneal surface?
Phosphate is used as a buffer, a solution to maintain the adequate pH of eye drops and prevent the decomposition of ingredients . Phosphate is also naturally found in human eyes, but an excessive level of phosphate from eye drops can lead to undesired effects.
In patients who have recently undergone eye surgeries, phosphates can be of a particular concern, although the risk of the following adverse event is low. Ocular surgeries damage the corneal surface, leading to an elevated level of calcium. The additional phosphate from eye drops can bind to calcium and form low-solubility calcium phosphate crystals. Continued use of phosphate-containing eye drops can cause deposition of these crystals. The consequences can be irreversible, and in severe cases, vision loss. 
Buffer solutions play a fundamental role of maintaining an adequate pH in lubricating eye drops. Hence, an optimal buffer must be selected carefully for both patient safety and performance. What other alternatives are available? Let’s take a closer look.
Two common buffers used to replace phosphate buffer are citrate and borate buffers. Citrate buffer has several benefits :
Does not induce calcification on the eye surface
Has corneal healing effects
Unlike phosphate-buffer, citrate buffer can help to heal wounds on the eye surface, which makes it suitable for patients recovering from ocular surgeries. Altogether, citrate buffer is a great alternative to phosphate buffer.
Similarly, borate buffer is another popular choice to replace phosphate buffer. Borate buffer does not form calcium deposits on the eye surface. It is also high tolerable and has antimicrobial activity. [4, 5] Hence, it is often contained in eye drops to avoid the use of phosphate buffer.
Where can you find phosphate-free lubricating eye drops?
HYLO® family of lubricating eye drops are preservative free and phosphate free. Using citrate or borate buffer, HYLO® lubricating eye drops prioritize patient safety. With high-quality sodium hyaluronate, HYLO® lubricating eye drops bring the best, unparalleled HYLO® experience for dry eye patients.
HYLO® family of lubricating eye drops are available for healthcare professionals and patients across Canada. Try now and feel the difference!
CandorVision™ – Your eyes are everything
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Questions and answers on the use of phosphates in eye drops. Doc Ref.: EMAOMP/753373/2012; http://www.ema.europa.eu/docs/enGB/documentlibrary/MedicineOA/2012/12/WC500136247.pdf
Sim P, Strudwick XL, Song Y, Cowin AJ, Garg S. Influence of Acidic pH on Wound Healing In Vivo: A Novel Perspective for Wound Treatment. Int J Mol Sci. 2022 Nov 7;23(21):13655. doi: 10.3390/ijms232113655. PMID: 36362441; PMCID: PMC9658872.
Schrage NF, Frentz M, Reim M. Changing the composition of buffered eye-drops prevents undesired side effects. Br J Ophthalmol. 2010 Nov;94(11):1519-22.
Iavazzo C, Gkegkes ID, Zarkada IM, Falagas ME. Boric acid for recurrent vulvovaginal candidiasis: the clinical evidence. J Womens Health (Larchmt). 2011 Aug;20(8):1245-55. doi: 10.1089/jwh.2010.2708. Epub 2011 Jul 20. PMID: 21774671.