A retrospective chart review of patients with evaporative dry eye and healthy individuals was performed. The study was approved by the Research Committee and the Bioethics Committee of the Health Sciences Division of the University of Monterrey. Requirement for a written informed consent was waived by the Comité de Investigación de la Vicerrectoría de Ciencias de la Salud de la Universidad de Monterrey (ref: 05132020-a-OFT-CC-CI) due to the retrospective observational nature of the study and information that allows the identification of the patient was not used, and adhered to the tenets of the Declaration of Helsinki.
The inclusion criteria for healthy individuals included an Ocular Surface Disease Index (OSDI) of <12 points, non-invasive tear film break- up time (NIKBUT) > 10 s, and no ocular surface staining, so patients with any type of dry eye was excluded. Patients with evaporative dry eye were included according to the criteria of the International Workshop on Meibomian Gland Dysfunction.6 Briefly, the patients were required to achieve an OSDI score > 12 points, NIBUT < 10 s, expressibility grades 1 to 3, and MG yielding liquid secretion (MGYLS) score > 1.6 The exclusion criteria for both groups were any uncontrolled systemic conditions and any history of refractive or eyelid surgery, corneal infection, or active ocular disease with the exception of dry eye, history of facial paralysis, or use of contact lenses in the past 7 days.
Evaluation of signs of dry eye
All assessments of signs were performed by one ophthalmologist specialist in cornea and ocular surface diseases (MGL). The following information was studied: self-administered OSDI questionnaire (Allergan, Irvine, CA) which had been validated in Spanish,24 for ocular surface staining 5 μL of 2% fluorescein diluted in saline solution was instilled in the cul-de-sac, and 2 minutes later, the corneal damage was assessed under the slit lamp using a cobalt blue and yellow filter. Stratification was performed using the classification of the Ocular Staining Score.25
Evaluation of non-invasive tear film breakup time (NIKBUT) was calculated with the Antares topographer (Construzionne Strumenti Oftalmici, Florence, Italy) according to the manufacturer’s guidelines. Briefly, two readings are provided at the end of every assessment: NIBUT-Initial, the time taken for the first appearance of a break in the tear film, and the NIBUT-Average is the average of the time taken to break-up in all the regions monitored over the 17 seconds. For the statistical analysis, the average of three consecutive measurements was used.
Meibomian gland characteristics
Meibomian gland characteristics of the upper and lower eyelids (UL and LL, respectively) was studied included secretion, number of expressible glands, and dropout rate and morphological characteristics of the central area of eyelids by infrared meibography with the Antares topographer.
According to the report by Arita et al.26 the eyelid margin characteristics were classified in an incremental way as normal, irregular, telangiectasias, orifice obstruction, and displacement of the mucocutaneous junction.
An expression instrument was used to evaluate the characteristics of the meibomian secretion of the LL. A force was applied to the nasal, central, and temporal regions of the LL, and each region contained eight consecutive MG orifices. The classification used to evaluate gland expressibility was 0= all glands expressible, 1 = 3–4 glands expressible, 2 = 1–2 glands expressible, 3 = no glands expressible. 27 In addition, the MGYLS score of the whole lid was determined according to Korb et al.13,28 The classification proposed by Bron et al.29 was used to evaluate the meibum characteristics as follows: clear (0), opaque (1), opaque with detritus (2), and toothpaste (3). Only the highest grade found among the expressed glands was recorded.
Meibography was performed according to the manufacturer’s protocols. The characteristics of the MG on infrared meibography were observed as aggregates in the form of grape-like clusters acini that are directed toward the palpebral margin in a straight or slightly tortuous line and that are hyperreflective. 30 The area of gland dropout was defined according to Pult et al. by “(1) the actual ending of glands, (2) the width of the area, defined to be between at least from the tear punctum, and the temporal border defined to be to the most well visible tarsal conjunctiva of the everted lid, and (3) the maximal depth of the area was estimated to be where glands would have ended in normal MG morphology”.11,13 including the ghost and fluffy areas, as suggested by Daniel et al. 7 For the quantification of the percentage of loss of the MG, we used the Phoenix software (version 3.2, Construzionne Strumenti Oftalmici, Firenze, Italy) in accordance with previous reports.26,31,32 Only images with good or fair quality of lid eversion were used according with Daniel et al. protocol.7
For the Meibomian gland morphology classification, the definition of DREAM protocol was used 7 (Figure 1A-D). Two readers graded each lid meibography image independently. The readers were blinded to all demographic, clinical, and treatment data. Only morphological characteristics with agreement between both readers was included.
Descriptive statistics were employed to describe the clinical signs using the SPSS software (v24 for Mac; IBM, Chicago, IL). Paired t-tests and Wilcoxon matched-pairs tests were employed to compare data with normal and non-normal distributions, respectively.
All analyses were performed separately for the upper and lower lids. Associations between continuous measures of MG features and signs were evaluated with linear regression, where the MG feature was the dependent variable. Associations between binary measures of MG features were evaluated with logistic regression, where the MG feature was the dependent variable. All regression models involving signs measured on a continuous scale and symptoms were calculated using the continuous values as independent variables. Regression models were adjusted for age and sex. All statistical analyses were performed with SPSS software (v24 for Mac; IBM, Chicago, IL).
We evaluated the correlations between all clinical parameters and morphological characteristics with logistic regression using the RStudio software (v4.0.2 for Windows, RStudio, Boston, MA). We controlled for sex (coded 1 = female; 0 = male) and age to account for factors that might bias our results.