Pre-emptive approach key to addressing dry eye
The ideal situation is to take care of this condition before patients are exposed to known hazards.
For the ophthalmic practitioner, prophylaxis is more commonly considered in cases requiring surgery, but another avenue for prophylactic treatment may be the recommendation of pre-emptive dry eye treatment before patient exposure to known drying hazards.
Corneal nerves and dry eye
The cornea is the most densely innervated surface of the human body, and these nerves play an important role in the production of tears.
The sensory feedback loop includes sensory traffic from the ocular surface to the central nervous system via the ophthalmic branch of the trigeminal nerve, integration with input from emotional and other nerve centers, and parasympathetic and sympathetic nervous stimulation of water movement and tear secretion. Specifically, research has demonstrated that the innervation of compensatory structures (eg, meibomian glands, goblet cells, lacrimal gland) may play a significant role in tear production.
Surgical procedures can interrupt neural functions via disruption of corneal nerves, damage of goblet cells by suction or alteration to central corneal shape. Researchers at Schepens Eye Research Institute have determined that those with lower levels of tear production preoperatively are more likely to develop chronic dry eye post-LASIK than those with higher quantities of tears. It may be helpful to recommend treatment prophylactically, to pre-empt the dryness that patients can experience in the months after surgery.
Furthermore, a retrospective case series in six patients who underwent both LASIK and blepharoplasty resulting in significant exposure keratopathy demonstrates the potential interplay between the two surgical procedures and dry eye.
In order to prevent the symptoms of dryness, clinicians should first probe for symptoms and test for clinical signs preoperatively. If dry eye is detected, the ideal situation is to address this dryness before surgery.
If the tests indicate ample ocular surface protection, a regular ocular lubricant used postoperatively is often helpful. Should dry eye result postoperatively, the clinician may choose to prescribe cyclosporine or steroids in addition to ocular lubricants.
Concomitant treatment of some ophthalmic formulations such as one of propylene glycol (PG), polyethylene glycol (PEG) 400 and the gelling agent HP-guar (Systane, Alcon) with cyclosporine A (Restasis, Allergan), for example, have demonstrated benefit. The lubricant eye drop has also demonstrated safety in post-LASIK use (including the day of surgery) and significantly longer tear film break-up time compared with saline 2 weeks postop.
Cataract surgery is also linked with dry eye. One study in 37 patients undergoing phacoemulsification and IOL implantation in China demonstrated significant decreases from baseline in Schirmer values and tear film break-up time, as well as increases in staining after surgery. Furthermore, the effect of cataract surgery in diabetic patients was recently reported to demonstrate significant increase from baseline in corneal staining lasting to 6 months postop, which authors speculated might be attributed to a combination of effects on tear production from both the disease and procedure.
Environmental conditions, including excessive wind, arid climates and urban pollutants, can be detrimental to ocular surface protection as well. Simply suggesting that patients introduce a humidifier during the winter months and avoid exposure to cigarette smoke (even for nonsmokers) could help ease their dryness symptoms. Furthermore, suggesting the use of tear supplements before experiencing arid climates or windy conditions may also be helpful.
Visual tasking and the blink
Visual display unit use, such as work done at a computer throughout the day, is another known menace of ocular surface integrity. Ocular surface protection can be measured via the ocular protection index (OPI) the ratio of tear film break-up time to interblink interval.
A patient with a healthy, protected ocular surface should display an OPI score of at least 1 because the patient typically blinks before tear break-up. Decreased blink rates such as those incurred during close work or visual display unit use, however, can result in an OPI score of less than 1, demonstrating insufficient protection. Furthermore, use of the interblink interval visual acuity decay test has demonstrated that dry eye subjects who spent significant amounts of time reading and working on a computer had higher keratitis scores compared with other dry eye subjects.
Ocular lubricants with lasting effects able to maximize optical effects upon instillation, as purported by a new PG/PEG 400/HP-guar tear incorporating sorbitol (Systane Ultra, Alcon), may be a good choice for those patients requiring tears during visual tasking. Recommending that patients use tears before and during visual tasking and that they remain aware of the importance of each blink is probably the best approach to treating this mode of dryness.
- Dartt DA. Control of mucin production by ocular surface epithelial cells. Exp Eye Res. 2004;78(2):173-185.
- Durrie D, Stahl J. A randomized clinical evaluation of the safety of Systane Lubricant Eye Drops for the relief of dry eye symptoms following LASIK refractive surgery. Clin Ophthalmol. 2008;2(4):973-979.
- Elwood P, Morgan G. Aspirin for all over 50 revisited. Heart. 2008;94(11):1364-1365.
- Guttman C. Artificial tear delivers high-performance dry eye therapy. Ophthalmology Times. 2008;33(14):25.
- Konomi K, Chen LL, Tarko RS, et al. Preoperative characteristics and a potential mechanism of chronic dry eye after LASIK. Invest Ophthalmol Vis Sci. 2008;49(1):168-174.
- Korn BS, Kikkawa DO, Schanzlin DJ. Blepharoplasty in the post-laser in situ keratomileusis patient: preoperative considerations to avoid dry eye syndrome. Plast Reconstr Surg. 2007;119(7):2232-2239.
- Li XM, Hu L, Hu J, Wang W. Investigation of dry eye disease and analysis of the pathogenic factors in patients after cataract surgery. Cornea. 2007;26(9 Suppl 1):S16-20.
- Liu X, Gu YS, Xu YS. Changes of tear film and tear secretion alter phacoemulsification in diabetic patients. J Zhejiang Univ Sci B. 2008;9(4):324-328.
- McCulley JP, Shine WE. The lipid layer of tears: dependent on meibomian gland function. Exp Eye Res. 2004;78(3):361-365.
- Ousler GW 3rd, Hagberg KW, Schindelar M, Welch D, Abelson MB. The ocular protection index. Cornea. 2008;27(5):509-513.
- Pflugfelder SC, Solomon A, Stern ME. The diagnosis and management of dry eye: a twenty-five-year review. Cornea. 2000;19(5):644-649.
- Rummenie VT, Matsumoto Y, Dogru M, et al. Tear cytokine and ocular surface alterations following brief passive cigarette smoke exposure. Cytokine. 2008;43(2):200-208.
- Sall KN, Cohen SM, Christensen MT, Stein JM. An evaluation of the efficacy of a cyclosporine-based dry eye therapy when used with marketed artificial tears as supportive therapy in dry eye. Eye Contact Lens. 2006;32(1):21-26.
- Toda IK. LASIK and the ocular surface. Cornea. 2008;27(9 Suppl 1):S70-76.
- Walker PM, Ousler GW III, Lane K, et al. The effect of increased blink rate on visual performance in dry eye patients. Invest Ophthalmol Vis Sci. 2008;49:E-abstract 5317.
- Shachar Tauber, MD, is the director of ophthalmology research at St. Johns Hospital and Clinic. He can be reached at 1229 E. Seminole, Suite 430, Springfield, MO 65807, U.S.A.; +1-417-820-9393; fax: +1-417-820-9725; e-mail: email@example.com. Dr. Tauber is on the speakers bureau for Alcon.