Pre-emptive approach key to addressing dry eye

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 recently 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 compound 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.

Priming patients

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.

References:

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• Shachar Tauber, MD, is the director of ophthalmology research at St. John’s Hospital and Clinic. He can be reached at 1229 E. Seminole, Suite 430, Springfield, MO 65807; 417-820-9393; fax: 417-820-9725; e-mail: shachar.tauber@mercy.net. Dr. Tauber is on the speakers’ bureau for Alcon.