Role of Tear Osmolarity in Dry Eye Symptoms After Cataract Surgery




Purpose


To analyze changes in tear osmolarity and the Ocular Surface Disease Index (OSDI) in patients after cataract surgery.


Design


Prospective, observational cohort study.


Methods


setting : Institutional. patient population : Fifty-two patients with a unilateral cataract (study eye) scheduled for surgery and good visual function in the fellow (control eye). Patients were excluded who were receiving chronic topical therapy, such as glaucoma medications, or had a history of previous ocular surgery. intervention : Examinations were performed preoperatively and 1 and 3 months postoperatively. At each visit, complete anterior and posterior segment examinations were performed. main outcome measures : Best-corrected and uncorrected visual acuities, tear osmolarity, and OSDI scores.


Results


The mean tear osmolarity values were, respectively, 305.63 ± 15.07, 305.70 ± 16.48, and 303.88 ± 11.75 mOsm/L at baseline and 1 and 3 months postoperatively ( P = .067), compared with 309.74 ± 15.92, 306.74 ± 13.22, and 303.19 ± 11.02 mOsm/L at the same times in the unoperated control eyes ( P = .064). Patients with normal osmolarity (<312 mOsm/L) and hyperosmolarity values (≥312 mOsm/L) had respective OSDI scores of 22.77 ± 15.73 and 36.02 ± 12.20 at baseline ( P = .01), 12.44 ± 12.44 and 14.45 ± 13.45 at 1 month ( P = .7), and 10.37 ± 11.11 and 16.48 ± 8.08 at 3 months postoperatively ( P = .01).


Conclusions


We did not find differences in tear film osmolarity between the operated eyes and the fellow unoperated control eyes at any time period during the study. Patients with tear osmolarity values of 312 mOsm/L or higher are more likely to have more ocular discomfort postoperatively. Ophthalmologists should consider evaluating tear osmolarity preoperatively, especially in highly demanding patients.


Dry eye disease (DED) is a multifactorial disease of the ocular surface that is associated with increased the tear osmolarity and some degree of inflammation of the ocular surface. Cataract surgery induces changes in corneal sensitivity and increases the symptoms of ocular foreign-body sensation, visual fatigue/fluctuation, and ocular redness, which are the symptoms usually associated with DED. Questionnaires designed to assess DED symptoms subjectively, such as the Ocular Surface Disease Index (OSDI), can assess the frequency and severity of dry eye symptoms and their impact on vision. The OSDI has good to excellent test-retest reliability, validity, sensitivity, and specificity. Unfortunately, any ocular condition affecting visual function, such as glaucomatous visual field loss, also affects the OSDI score, at least regarding the items related to visual tasks. In other words, cataract surgery per se is expected to have a dual effect on this questionnaire by decreasing the OSDI score because the visual function is improved but by worsening the ocular discomfort-related items because of cataract surgery–induced DED.


Tear hyperosmolarity is diagnostic of DED and is the most relevant single objective diagnostic sign. Further, tear osmolarity has a higher correlation coefficient with DED severity than other objective diagnostic tests commonly used in clinical practice, such as conjunctival staining, the meibomian score, and the Schirmer test.


Few studies have analyzed DED symptoms in patients after cataract surgery. These studies have shown that cataract surgery worsens the dry eye symptoms in patients with preexisting DED and induces dry eye symptoms in patients without preexisting DED, at least for the first 2 months postoperatively. Only 1 study has reported changes in tear osmolarity after phacoemulsification. Those authors found that the tear osmolarity increased in the early postoperative period compared with preoperatively. Nevertheless, in that study, a nanoliter osmometer using freezing point depression of tear microsamples was used. However, the TearLab osmometry system (TearLab Corporation, San Diego, California, USA), which is based on electrical impedance “lab-on-a-chip” nanoliter technology, has higher specificity than the freezing point depression techniques. The TearLab osmometry system allows calculation of the tear osmolarity using a very small tear volume (50 nanoliters) and is a quick and accurate measurement of osmolarity of the tear film in a clinical setting. For these reasons, we analyzed the changes in tear osmolarity (using the TearLab system) and the OSDI in patients undergoing cataract surgery.


Methods


This was a prospective, observational study. The Institutional Review Board of the Principe de Asturias University Hospital approved this study, which was conducted in accordance with the principles of the Declaration of Helsinki. All patients provided written informed consent before starting the study.


Inclusion and Exclusion Criteria


The inclusion criteria included the presence of a unilateral cataract in the study eye scheduled for surgery and good visual function in the fellow control eye. Patients were excluded who had a diagnosis of severe dry eye and were treated with topical cyclosporine and cauterization or insertion of silicone plugs in the lacrimal puncta; those treated chronically for glaucoma; those with a history of any previous corneal surgery; and those who underwent a previous ocular surgery performed less than 1 year before the recruitment examination.


Experimental Protocol


In all cases, an experienced surgeon performed the same surgical technique, that is, standard phacoemulsification with implantation of a posterior chamber intraocular lens (IOL) under topical anesthesia. A 2.75-mm clear corneal incision and a side port of about 1 mm, located 90 degrees away from the main incision, were made. A foldable single-piece acrylic hydrophobic intraocular lens (Alcon SN; AlconCusi, Barcelona, Spain) was implanted in the capsular bag. No relevant intraoperative complications developed in any case. All patients were treated with the same postoperative regimen of Tobradex eye drops (AlconCusi) for the first 4 postoperative weeks. The patients were told not to apply any eye drop at least 1 hour before each postoperative visit.


The examinations were performed preoperatively and 1 and 3 months postoperatively. At each visit, a trained optometrist recorded the best-corrected and uncorrected visual acuity (VA) levels, tear osmolarity, and the OSDI score. In addition, an experienced ophthalmologist performed complete eye examinations, including an anterior segment evaluation, intraocular pressure measurement using Goldmann applanation tonometry, and dilated fundus examination at baseline and 1 month postoperatively.


Tear osmolarity was evaluated using the TearLab system. Briefly, the osmometer is based on electrical impedance using lab-on-chip technology that only needs a very small tear sample (50 nL) obtained directly from the inferior tear meniscus.


The OSDI questionnaire was used to analyze the presence of DED symptoms, with scores that range from 0 to 100. Scores from 0 to 25 are considered normal; scores exceeding 25 indicate the presence of dry eye symptoms and/or visual difficulties performing daily tasks.


Cornea and conjunctival fluorescein staining was assessed using the Oxford scale.


Data normality was checked using the Kolmogorov-Smirnov test. The 2-tailed unpaired Student t test was used for single comparisons, and the repeated-measures analysis of variance test was used to analyze the changes in continuous variables during follow-up. The Bonferroni correction was used when appropriate. Linear regression analysis was used to analyze the relationship between tear osmolarity and the OSDI score. P ≤ .05 was considered significant.




Results


This study included 52 consecutive patients (28 men, 24 women) who met the inclusion/exclusion criteria and agreed to participate. The patient demographics are shown in Table 1 .



Table 1

Demographic Data (Baseline) of Patients (N = 52) Included in Study of Role of Tear Osmolarity in Dry Eye Symptoms After Cataract Surgery

















































Male Female P Value
Patients (n) 28 24
Age (y) 70.17 ± 7.86 71.20 ± 8.11 .50
BCVA
S eye 0.49 ± 0.20 0.38 ± 0.21 .07
C eye 1.11 ± 1.35 0.78 ± 0.25 .20
IOP (mm Hg)
S eye 15.07 ± 2.63 14.85 ± 3.24 .70
C eye 15.11 ± 2.45 14.00 ± 4.39 .2

BCVA = best-corrected visual acuity; C eye = control eye; IOP = intraocular pressure; S eye = study eye.


No significant differences in the mean tear osmolarity were found between men and women in any of the measurements performed. Nevertheless, significantly ( P = .01) more women had hyperosmolar tear values using the 312 mOsm/L cutoff level ( Table 2 ).



Table 2

Osmolarity and Ocular Surface Disease Index by Sex, Study Eyes

























































































Measurement Male Patients (N = 28)
Mean ± SD
Female Patients (N = 24)
Mean ± SD
P Value
Osmolarity
Basal 304.03 ± 14.51 307.50 ± 15.81 .1
1 M 306.44 ± 19.99 304.82 ± 11.45 .7
3 M 303.39 ± 12.27 304.45 ± 11.36 .7
OSDI
Basal 20.10 ± 14.27 33.62 ± 19.61 .06
1 M 10.69 ± 11.40 16.49 ± 16.43 .1
3 M 9.07 ± 5.74 15.45± 9.89 .05
Oxford
Basal 0.08 ± 0.28 0.04 ± 0.21 .50
1 M 0.12 ± 0.32 0.09 ± 0.36 .537
3 M 0.02 ± 0.13 0.13 ± 0.34 .026
BCVA
Basal 0.49 ± 0.20 0.38 ± 0.21 .07
1 M 0.94 ± 0.09 0.86 ± 0.15 .02
3 M 0.94 ± 0.09 0.87 ± 0.15 .02

BCVA = best-corrected visual acuity; M = months postoperative; OSDI = ocular surface disease index; SE = spherical equivalent.


No significant differences were found between men and women at any visit in the OSDI score, except during visit 3, when the OSDI score was significantly ( P = .05) higher in women ( Table 2 ).


We did not find any differences in tear osmolarity between baseline and the 1- and 3-month postoperative visit in the study or control eyes, with values of 309.74 ± 15.92, 306.74 ± 13.22, and 303.19 ± 11.02 mOsm/L, respectively. The OSDI score improved significantly between baseline and the 1- and 3-month postoperative visits ( Table 3 ). The best-corrected VA in the study eye was significantly better at 1 and 3 months compared with baseline, as expected after cataract surgery ( Table 3 ). No change in the VA was found in the unoperated eyes.


Jan 5, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Role of Tear Osmolarity in Dry Eye Symptoms After Cataract Surgery
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