Corneal Refractive Surgery-related Dry Eye

Risk Factors and Management

Louis Tong; Yang Zhao; Ryan Lee

Disclosures

Expert Rev Ophthalmol. 2013;8(6):561-575. 

In This Article

Pre-operative Risk Factors & Assessment

Prior to any corneal refractive surgery, it is crucial to take a comprehensive history during the consultation and to assess the patient's existing tear function or dry eye status. Demographic factors, lifestyle, medical and surgical history should be elicited to understand the risk profile of the patient seeking refractive surgery.

Demographic & Lifestyle Factors

Age, female gender and East Asian race are possible predisposing factors to post-operative dry eye. Age was found to be inversely associated with corneal sensitivity,[48] but older age was not correlated to the development of post-operative dry eyes.[49] The age range examined in the studies was from 27 to 47 years. Female gender and East Asian ethnicity (in contrast to Caucasian ethnicity) are risk factors for post-LASIK dry eye, as evidenced by more severe symptoms and poorer tear function post-operatively.[7,48]

In a separate study, age and gender were not found to predispose to post-LASIK dry eye, but this study diagnosed dry eye purely on corneal fluorescein staining.[8] Ethnicity as a risk factor may be confounded by other factors. These include racial differences in lid and orbital anatomy, blinking dynamics; higher pre-operative myopia and attempted refractive correction; and poorer pre-existing tear film parameters in East Asians. The effects of age, gender and race have been reviewed elsewhere and similar conclusions were obtained.[8,50,51]

History of contact lens wear is also important. Patients with contact lens intolerance may have underlying dry eye. Long duration of contact lens use is a risk factor for otherwise normal individuals to develop dry eye[2,52] and similarly predisposes post-LASIK patients to chronic dry eye defined as dry eye persisting beyond 6 months.[49] The duration of contact lens wear in this study ranged from 3 to 23 years.

Cigarette smoking should also be considered. A study published in 2013 discovered that contact lens wear and chronic cigarette smoking positively correlate with TGF-β1 and VEGF tear levels and delayed corneal re-epithelialization.[53] There is no evidence that smoking cessation improves the tear outcome after LASIK.

Medical & Surgical History

Pre-operative assessment should also focus on these factors: previous diagnosis of dry eye, frequency and intensity of symptoms of pre-operative dry eye disease, severity of pre-operative myopia, presence of other ocular inflammatory disease, collagen vascular disease (CVD) (especially Sjogren syndrome) and history of prior blepharoplasty.

Increased severity of pre-operative myopia was shown to be a risk factor for chronic post-LASIK dry eye, defined as a corneal fluorescein staining score of three or more[8] (relative risk of 0.88 per diopter increase in pre-operative spherical equivalent). This study examined -1 to -7D of myopia in 35 adults. Studies have shown that incidence of dry eye is greater in patients with a history of allergy. This was concluded in a retrospective study of 572 individuals in an elderly population (age range: 43–86).[54] Incidence or prevalence of dry eye in atopic individuals has not been documented. The higher incidence of inflammatory complications of LASIK, such as Diffuse Lamellar Keratitis, in atopic patients suggests that these patients have an abnormally strong inflammatory response to LASIK.[55] Caution is advised in performing LASIK on patients with history of atopic conditions such as asthma, atopic dermatitis and rhinoconjunctivitis due to possible shared pathways of pathophysiology between atopy and post-LASIK dry eye. Evidence of common pathways includes NGF hyperexpression, which has been documented in patients with Vernal Keratoconjuncitivitis.[56] However, more extensive studies have to be done to establish how the mechanisms of ocular allergy and post-LASIK dry eye overlap and interact. Given the possibility of increased risk in atopic patients, it is advisable to control and stabilize the patient's allergic condition before performing LASIK.

The FDA has named CVD a LASIK contraindication, as many CVDs can have a component of dry eye[57] and usually of higher severity, as reported in patients with rheumatoid arthritis.[58] However, research has produced conflicting evidence on the safety profile of LASIK on this group of patients. One paper[57] has reviewed studies on LASIK in patients with CVDs, in particular the four major diseases: Sjogren's syndrome, rheumatoid arthritis, systemic lupus erythematosus and seronegative spondyloarthropathies. This study concluded that together with stringent selection of only patients with mild, stable and well-controlled systemic condition, LASIK surgery may be safe in most patients with CVD with the exception of Sjogren's syndrome.

Even in cases of Sjogren syndrome with severe dry eyes diagnosed prior to LASIK, good post-operative refractive power and tear function outcomes were achieved when these patients were appropriately managed pre- and post-operatively with artificial tears, topical autologous serum and punctal occlusion.[59] However this was observed in a study of very small sample size (3 patients, 6 eyes). One case report has described two cases of early-stage Sjogren syndrome patients who were well-controlled for both systemic condition and dry eye, but still suffered from severe post-LASIK dry eye complicated with punctate epithelial erosion and regression of the initial refractive error at 2 and 15 months post-operatively. Despite 10 months of intensive dry eye treatment, the patients' dry eye, improved only marginally.[60] There are no previous studies on post-LASIK dry eye in thyroid disease patients or graft-versus-host disease patients.

Despite the numerous studies supporting that LASIK is safe in patients with CVD, it is still advisable to avoid photorefractive surgery in these patients. If patients insist on surgery, they should be counseled about their risk profile, as well as briefed about the importance of compliance to pre- and post-operative management with artificial tears, topical autologous serum, punctal occlusion, etc. Consultation with the rheumatologist is also necessary to assess the severity and stability of the patient's condition.

While no studies have been conducted to assess the risk of post-LASIK dry eye in patients with a history of blepharoplasty, we believe patients who have had previous blepharoplasty should be stringently assessed before proceeding with LASIK, as dry eye may be a common complication after blepharoplasty.[61]

In the lateral view, a vertical line dropped from the supraorbital rim to the infraorbital rim is usually in tangent with the corneal surface. If the corneal surface protrudes beyond this line, it is termed a negative vector.[62] Looking out for a negative vector of the orbit may also be helpful in assessing risk of dry eye. A negative vector is associated with greater incidence of scleral show and lower lid descent after lower lid blepharoplasty. Nocturnal lagophthalmos can occur after blepharoplasty[63] and should also be assessed in patients.

Assessment of Pre-operative Tear & Cornea Function

The clinical examination should include factors aggravating dry eye, such as reduced corneal sensitivity, conjunctival hyperemia, chemosis, and lid disease such as blepharitis or meibomian gland disease. Abnormal lid anatomy and blink dysfunction (e.g., reduced blink rate) must be actively searched for during the pre-operative period. Lagophthalmos may occur for various reasons including facial nerve palsy.

Pre-existing dry eye disease is a major risk factor for post-LASIK dry eye of higher severity.[10,42,48,50,64] As such, for these patients, pre-operative optimization of the ocular surface must be performed so that any negative impact of the surgery on dry eye will be minimized.[10,50,65,66] Ocular surface optimization, including the treatment of contributing conditions like meibomian gland dysfunction (MGD), will be covered under the 'Management' section.

Objective dry eye signs can be measured with the traditional tear and corneal function tests, consisting of Schirmer's test to assess tear secretion (basal and reflex); tear break-up time (TBUT) to assess tear film stability; and corneal fluorescein dye staining to assess corneal epithelial integrity. They have all been demonstrated to be relevant risk factors for chronic post-LASIK dry eye.[48] Among these, the pre-LASIK Schirmer score is of particular importance and its pre-operative value is significantly correlated with post-operative TBUT (r = 0.504, p = 0.02) for up to 9 months in a study.[42] Schirmers I of less than 10 mm (at 5 min) was associated with increased risk (relative risk: 1.58; 95% CI: 1.10–2.26) of post-operative dry eye at one month post-operatively.[64] There has been no study using a receiving operating curve approach to examine the optimal Schirmer test threshold to detect post-LASIK dry eye.

Certain groups performed Rose Bengal dye staining of the conjunctiva.[20,27,42,59,67] This has not proven to be mandatory for the purpose of routine assessment. It is also a potential source of ocular irritation, and hence its use does not seem warranted.

Corneal sensitivity, although not a routine component of dry eye diagnosis, is valuable because of its role in the pathogenesis of LASIK-induced dry eye as previously mentioned. Assessment is performed using the Cochet-Bonnet esthesiometer. Three studies used non-contact gas esthesiometers for corneal sensitivity assessment.[68–70] Though these are proven to give results that are consistent with those of Cochet-Bonnet esthesiometry, the gas esthesiometers may not be widely available for use in LASIK clinics due to their cost. There have been no studies that found correlation between pre-operative corneal sensitivity and post-operative tear function.

InflammaDry, a rapid point-of-care diagnostic test to detect elevated matrix metalloproteinase 9 levels, has shown good sensitivity (85%) and specificity (94%), in detecting dry eye.[71] However, it should be noted that the diagnostic criteria for dry eye were strict in this study, and required positive OSDI, TBUT, Schirmer's test and corneal staining findings for dry eye. In the context of post-LASIK dry eye, InflammaDry may have a role in patient selection for pre-operative ocular surface optimization and for anti-inflammatory dry eye treatment.[72]

Other diagnostic aids to consider include tear osmolarity testing with the TearLab Osmolarity System. Use of this device to diagnose and assess dry eye has been reviewed favorably,[73] and has been found to be useful in assessment of LASIK-related dry eye.[31]

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