Meibomian gland dysfunction (MGD) is an umbrella term that encompasses several meibomian gland disorders, ranging from congenital to acquired. Disruption of meibomian gland function negatively impacts both the quality and quantity of meibum secreted, which in turn affects ocular surface health through changes in tear film composition. Increased tear evaporation, hyperosmolarity, inflammation, and ocular surface damage can subsequently occur. This may cause discomfort, visual disruption, and sensation of dry eye. This review article discusses the pathology, causes, and ocular surface impact of MGD, as well as its relationship to dry eye.

Purpose Serotonin, a neurotransmitter known to be involved in nociceptor sensitization, is present in human tears. The purpose of this study was to correlate tear serotonin levels, as a marker of nociceptor sensitization, to facets of dry eye (DE) including symptoms and signs. Design Cross-sectional study Participants Sixty-two patients with normal eyelid and corneal anatomy were prospectively recruited from a Veterans Administration Ophthalmology Clinic over 11 months. Methods DE symptoms (Ocular Surface Disease Index [OSDI]), signs (tear break-up time [TBUT], corneal staining, and Schirmer’s score), and clinical descriptors of neuropathic ocular pain (NOP) (sensitivity to light and/or sensitivity to wind) were assessed. For tear analysis, each patient’s tears were collected after instilling 50µl of sterile saline to the lower cul-de-sac of each eye and using capillary action microcaps to collect the ocular wash. Tear serotonin levels were measured using enzyme-linked immunosorbent assay. Main Outcomes Measured Correlations between tear serotonin concentrations and DE symptoms and signs. Results The mean age of the population was 61±14 years and 84% (n=52) of the patients were male. Serotonin concentrations negatively correlated with Schirmer’s scores (r=−0.28; p=0.02), but did not correlate with other DE parameters, such as OSDI scores, sensitivity to light or wind, TBUT, or staining. According to our hypothesis, we divided patients into groups based on both DE symptoms and aqueous tear production; serotonin concentrations were found to be significantly higher in DE group 1 (OSDI≥6 and Schirmer’s<8) compared to both DE group 2 (OSDI≥6 and Schirmer’s≥8) and controls (OSDI<6 and Schirmer’s≥8). Patients in the DE group 2 more frequently complained of sensitivity to light (64%) and wind (67%) compared to the DE group 1 (40% and 60%, respectively) and controls (8% and 17%, respectively). Conclusion Patients with DE symptoms and aqueous tear deficiency had higher tear serotonin levels compared to those with DE symptoms but normal tear production and those without DE symptoms.

The presence of NCch associates with dry eye symptoms, abnormal tear parameters, and impacts quality of life compared with non-NCch and no-Cch. Based on these data, it is important for clinicians to look for Cch in patients with symptoms of dry eye.

Although the ORange most often predicted to within ±0.5 D of emmetropia, no method was able to achieve this accuracy more than 50% of the time. Predictions for eyes after RK were worse than for other types of refractive procedures.

This study demonstrates the visual and structural outcomes that returned to near baseline after Intacs explantation in keratoconic eyes.