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10 April, 2018
Tear film quality is the most important factor to achieve high-quality visual outcomes in refractive and cataract surgery, thus its assessment and managing cornerstone to deliver the excellent visual results the patients expect.
Dry eyes are more likely to have large optical aberrations than those with a normal tear film,1 and can lead to inaccurate intraocular lens calculations, increasing the risk of postoperative complications or infection. Undiagnosed dry eye, one of the main syndromes of the ocular surface disease (OSD), may worsen after surgery.1
Cataract surgery itself may also induce or worsen dry eye disease.2,3 It has been reported that 3% to 33% of patients with cataracts have OSD. Left them untreated may affect the postoperative vision outcomes and reduce patient satisfaction after successful cataract surgery.4Virtually, all patients who have corneal refractive surgery have dry eye symptoms after the procedure, and 10% to 30% will have persistent dry eye after LASIK.4
Therefore, to achieve patient satisfaction it is important to take the necessary steps to identify dryness and use effective treatment strategies before performing preoperative measurements or surgery.
Because many patients with an unstable tear film are asymptomatic or have less obvious dry eye, surgeons must perform preoperative measurements with more than one device and check for discrepancies and image stability. Ophthalmologists have a range of available tools to help them detect OSD and identify its origin. Traditional diagnostics include external examination, meibography, Shimers’s test, conjunctival and corneal staining, and tear breakup time (TBUT). In addition, surgeons should examine the eye for lid parallel conjunctival folds, a sign of severe dry eye.
The first step is to note patients’ blink frequency. Some older patients do not blink, particularly if they have Parkinson’s disease or are receiving psychopharmacological treatment for psychosis or depression. Symptoms such as foreign body sensation, tearing, and redness are also present in other common pathologies, thus it is important to discard hypersensitivity or infectious conjunctivitis. Meibomian gland disease (MGD) impacts patients’ tear film stability. Clinical signs of MGD include irregular lid margin, lid margin thickening, and meibomian gland orifice pouting.
The TBUT is one of the most useful tests to assess tear film function. It is recommended to perform it before any other examination. Other tests may identify anatomical, biological and structural changes, such as tear osmolarity, tear volume, MMP-9, and tear production. To standardize the procedure, ophthalmologists should always use the same light intensity. The functional status of the tear film influences whether the patient has good, intermediate, or poor vision. The Report of the Definition and Classification Subcommittee of the International Dry Eye Workshop defined tear hyperosmolarity and tear film instability as the causes of dry eye.4
A double-pass instrument is the most important tool in identifying dry eye. Performing a series of objective scatter measurements, Yu et al. reported that this method may be even more suitable to detect dry eye than tear breakup time, so it may be useful in identifying very early asymptomatic cases.5
Tear osmolarity provides important information in guiding treatment once the tear film function has been determined. Lempet al. stated that tear osmolarity is the most useful test to detect and classify dry eye.4
The interferometry measures tear film thickness, blink rate, and partial blink rate. A relatively thin tear film lipid layer has been correlated with severe symptoms of dry eye.6
Treatment options for aqueous deficiency dry eye include artificial tears (most common treatment), hyaluronic acid (binds water and supports epithelial regeneration), punctual plugs, autologous serum, anti-inflammatory topical treatment, oral omega-3 supplements, and cholinergics such as oral pilocarpine. Cyclosporine may be useful as second-line treatment in severe cases,7which may not be candidates for refractive surgery. In an unstable tear film, is interesting to apply three months of treatment with ocular lubricants to optimise the ocular surface before repeat the measurements.
The MGD may be treated with artificial tears (with or without lipid component), lid hygiene, topical azithromycin, systemic doxycycline derivatives, oral omega-3 supplements, in-office lid cleansing with a hand-held device, thermal pulsation, or meibomian gland probing. Patients with severe MGD often benefit from preservative-free steroids to improve surface quality. As in more mild forms of MGD, patients may also benefit from slow-release tetracycline or topical azithromycin.
Regardless the intervention chosen for managing OSD, it is important to advise patients with moderate disease that their OSD may worsen after cataract surgery. If patients are cautioned beforehand, they are not surprised if symptoms occur. In cases of severe OSD, it may be necessary to postpone surgery until the surface is optimised.
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