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Introduction: Aqueous humor and its dynamics (AHD) serve numerous functions to sustain ocular health and clear vision. Current methods to assess AHD have led to improved understanding of ocular physiology, pathologies caused by abnormal intraocular pressures (IOP), and treatments to return IOP to healthy levels. However, the assumptions and limitations inherent in these methods have been problematic. New methods on the horizon are showing promise to greatly advance the field. Areas covered: This review summarizes AHD assessment techniques in use today including the noninvasive methods of fluorophotometry, tonometry, tonography, venomanometry, and invasive methods of cannulation, infusion, dissection. It also mentions emerging methods utilizing advanced imaging methods, smart phones, cameras, and software. Expert opinion: Soon new techniques will become available to measure each parameter and even subparts of each parameter of AHD with increased speed, accuracy, and safety. Along with these new methods and the data they generate could emerge the next version of the Goldmann Equation. These new methods would make AHD an important tool in the clinic for precision medicine and in the lab for exploring AHD on a new level. [ABSTRACT FROM AUTHOR]

Background: The aim of this study was to investigate the utility of strip meniscometry tube (SMTube) for the quantitative assessment of the tear film, by comparing it to measurements of tear turnover rate using the gold standard method, fluorophotometry. Also, to determine the viability of this test as a diagnostic tool for aqueous deficient dry eye (ADDE), to inform appropriate clinical management.Methods: Thirty-two participants (15 ADDE; 17 non-ADDE) were recruited. Tear turnover rate of the right eye of each subject was conducted with an automated scanning fluorophotometer and SMTube test was conducted. Tear meniscus height was assessed using a slitlamp biomicroscope and eyepiece graticule.Results: Significant differences between the ADDE and the non-ADDE groups were found for all measures: tear turnover rate 7.9 ± 1.8 versus 19.6 ± 5.9 per cent/minute (p < 0.001), SMTube 3.2 ± 1.1 versus 5.7 ± 2.3 mm (p = 0.001) and tear meniscus height 0.18 ± 0.05 versus 0.23 ± 0.04 mm (p = 0.004). Moreover, significant correlations were found between tear turnover rate and SMTube (rho = 0.78, p < 0.001), tear turnover rate and tear meniscus height (rho = 0.54, p < 0.001) and SMTube and tear meniscus height (rho = 0.47, p < 0.01). Using a receiver operating characteristic curve, SMTube showed a sensitivity of 67 per cent and a specificity of 88 per cent for the diagnosis of ADDE.Conclusion: Given its performance, availability, speed and the fact it is relatively cheap, the study shows that the SMTube can be used as an alternative to fluorophotometry to assess tear production. It appears from the results that SMTube is a viable minimally invasive test for the diagnosis of ADDE. [ABSTRACT FROM AUTHOR]

Introduction: The aim is to provide a summary of methods available for the assessment of tear turnover and tear clearance rates. The review defines tear clearance and tear turnover and describes their implication for ocular surface health. Additionally, it describes main types of techniques for measuring tear turnover, including fluorescein tear clearance tests, techniques utilizing electromagnetic spectrum and tracer molecule and novel experimental techniques utilizing optical coherence tomography and fluorescein profilometry. Areas covered: Internet databases (PubMed, Science Direct, Google Scholar) and most frequently cited references were used as a principal resource of information on tear turnover rate and tear clearance rate, presenting methodologies and equipment, as well as their definition and implications for the anterior eye surface health and function. Keywords used for data-search were as follows: tear turnover, tear clearance, fluorescein clearance, scintigraphy, fluorophotometry, tear flow, drainage, tear meniscus dynamics, Krehbiel flow and lacrimal functional unit. Expert commentary: After decades, the topic of tear turnover assessment has been reintroduced. Recently, new techniques have been developed to propose less invasive, less time consuming and simpler methodologies for the assessment of tear dynamics that have the potential to be utilized in clinical practice. [ABSTRACT FROM AUTHOR]

Background: This study was designed to examine diurnal variations in tear film break-up time (BUT) and maximum blink interval (MBI) and to assess two different ways of calculating these variables on video recordings of the BUT test interpreted with the help of especially designed software. The repeatability of interpreting BUT video recordings was also addressed.Methods: Twenty-six healthy young adults were enrolled after ruling out dry eye according to a battery of tests (ocular surface disease index, McMonnies questionnaire, Schirmer test, phenol red test and corneal staining). BUT and maximum blink interval were determined on video-recordings of the BUT test conducted over a day in four sessions (9.30 am, 12.30 pm, 3.30 pm and 6.30 pm). In each session, the test was repeated three times to give three videos in which three BUT and MBI values were obtained by a masked observer. BUT and MBI were determined by averaging the three measurements and by averaging only the two closest measurements. Finally, two further experienced observers re-examined the videos to assess the repeatability of the BUT measurements made.Results: No diurnal variation in BUT was observed regardless of whether three or two video measurements were averaged. Significant correlation was detected between BUT and MBI. Inter-observer repeatability was better when BUT times were no longer than 15 seconds.Conclusions: Tear film BUT was not influenced by the time of day and moderate to strong correlation with MBI was observed in all four sessions. The software-assisted method proved useful and identified the need to clarify the BUT end-point and to limit the test to 15 seconds to improve observer repeatability. [ABSTRACT FROM AUTHOR]

Purpose: Unstable tear film characterized by shorting of tear break-up time (BUT) is associated with discomfort and dryness in contact lens wearers. The glycocalyx is thought to be crucial in maintaining the wettability and lubrication of the ocular surface. We evaluated the ocular surface glycocalyx in soft contact lens (SCL) wearers using a fluorescein-labeled wheat germ agglutinin (F-WGA) as a marker to demonstrate the ocular surface glycoconjugatesin vivo. Methods: Twenty experienced SCL wearers and 20 healthy volunteers with no history of CL wearing (controls) were enrolled in the study. After applying a 5% F-WGA solution to the eyes of study individuals, fluorescent intensities in their respective central corneas were measured by fluorophotometry. The relationship between F-WGA intensity in the corneal surface and clinical parameters associated with contact lens wear were analyzed. Results: F-WGA fluorescence intensity in the SCL group was 418.5 ± 103.3, which was significantly lower than that of the controls (825.0 ± 179.8;p < 0.0001, Mann–Whitney test). F-WGA fluorescence intensity was not correlated with Schirmer’s test values or age, whereas a statistically significant correlation between F-WGA fluorescence intensity and tear film BUT was observed (r = 0.77,p < 0.0001). The decrease in F-WGA fluorescence intensity could be reversed by discontinuation of SCL use. Conclusion: Reduction and/or compositional alteration of ocular surface glycocalyx may be one of the causative factors of SCL-induced eye dryness. [ABSTRACT FROM PUBLISHER]

The formation of hypochlorous and hypobromous acids by heme peroxidases is a key property of certain immune cells. These products are not only involved in defense against pathogenic microorganisms and in regulation of inflammatory processes, but contribute also to tissue damage in certain pathologies. After a short introduction about experimental approaches for the assessment of the halogenating activity in vitro and in cell suspensions, we are focusing on novel applications of fluorescent dye systems to detect the formation of hypochlorous acid (HOCl) in leukocytes. Special attention is directed to properties and applications of the non-fluorescent dye aminophenyl fluorescein that is converted by HOCl, HOBr, and other strong oxidants to fluorescein. This dye allows the detection of the halogenating activity in samples containing free myeloperoxidase and eosinophil peroxidase as well as in intact granulocytes using fluorescence spectroscopy and flow cytometry, respectively. [ABSTRACT FROM AUTHOR]

Novel silica gel-immobilized rhodamine (SGR) anchored by hydrazinium hydrate was synthesized. The selectivity and adsorption ability of the SGR for metal cations were investigated with fluorophotometry and atomic absorption spectrophotometery, respectively. The SGR exhibits high selectivity and adsorption capacity for Hg2+. The maximum static adsorption capacity of the SGR for Hg2+was 25.8μmol g−1. The linear response range covers a concentration range of Hg2+from 20 ppb to 2000 ppb and the detection limit is 10 ppb. The determination of Hg2+in real water samples displays satisfactory results, and the SGR can be used repeatedly by treating with a solution of tetrabutylammonium hydroxide. [ABSTRACT FROM AUTHOR]

Several non-invasive techniques for dry eye diagnosis have been developed in the past decade. These include quantitative assessment of tear volume, tear film stability, tear dynamics, and integrity of ocular surface epithelium. A combination of meniscometry and interferometry is useful for proving focal dry eye, by confirming whether or not tears at the meniscus have an effect on the ocular surface. Interferometer is also useful to evaluate tear dynamics on soft contact lenses. Fluorophotometry is useful for assessing the severity of dry eye from the view point of corneal epithelial barrier function and measuring the tear turnover rate. Both video-meibography and meibometry are useful for screening meibomian gland dysfunction. The advances in these techniques accumulate knowledge regarding pathophysiology of dry eye and allow precise diagnosis of dry eye. More targeted treatment will become feasible based on the clearer pathophysiology. [ABSTRACT FROM AUTHOR]

PURPOSE. The buffering action of human tears is thought to be important to keep its pH constant. We measured the change in pH in the precorneal tear film in vivo when the acidic solution is challenged, using a fluorophotometric technique. METHODS. Twelve eyes from 6 healthy subjects were entered in this study. Each subject was pretreated with either one drop of 0.4% oxybuprocaine for once (light anesthesia), three times (deep anesthesia), or none (controls). The measurement was initiated by instilling 20 μl of 0.067 M phosphate buffer at pH 5.5 containing 2 mM bis-carboxyethyl-carboxyfluorescein free acid, a pH sensitive dye, into the subject's eye. The pH was determined by the ratio of fluorescent intensities at two excitation wavelengths (490 and 430 nm). pH recovery time (PHRT) as defined by the time required for pH to reach 95% of pH at equilibrium was used for the marker of tear buffering action. Tear turnover rate was also determined using the fluorescent decay curve at 430 nm, which was independent of pH, but dependent on dye concentration. RESULTS. Immediately after the instillation, the pH value in the tear film was around 6.0–6.5 in all cases. The tear film rapidly became more alkaline, reaching its normal value in 2.3 ± 0.5 min in untreated eyes. The pretreatment with 0.4% oxybuprocaine retarded the neutralization process. A single regression analysis revealed that the PHRT had a significant negative correlation with the tear turnover rate (r = -0.78). Conclusions. Our results suggest that the neutralization process of tears largely depends on the tear turnover rate. The buffering action of tears in vivo consists of the tear turnover as well as its chemical buffering capacity. [ABSTRACT FROM AUTHOR]

Background: The aim was to investigate the efficacy of mechanical meibomian gland squeezing combined with eyelid scrubs and warm compresses in participants with moderate and severe meibomian gland dysfunction (MGD).Methods: In this prospective, uncontrolled, open label, intervention study, 32 eyes of 32 participants with moderate and severe MGD were treated with mechanical squeezing of meibomian glands in combination with eyelid scrubs and warm compresses. We evaluated tear film break-up time (TBUT), corneal and conjunctival fluorescein staining scores, biomicroscopic examination of lid margins and meibomian glands, Ocular Surface Disease Index (OSDI) questionnaire and tear film lipid layer thickness determined via an interferometer before initiating treatment and after one month of treatment.Results: There were significant improvements in TBUT, corneal and conjunctival fluorescein staining scores, lid margin abnormality, meibum quality and expressibility, OSDI and MGD stage after mechanical meibomian gland squeezing combined with eyelid scrubs and warm compresses (p < 0.001 for TBUT, corneal fluorescein staining scores, Dry Eye Workshop score, Oxford staining score, lid margin abnormality, meibum quality, expressibility, OSDI and MGD stage and p = 0.001 for conjunctival fluorescein staining scores). There were no significant differences in lipid layer thickness or interferometer-derived parameters before treatment and after one month of treatment. Palpebral conjunctival erosion detected after the squeezing treatment resolved spontaneously in all participants.Conclusions: Mechanical squeezing of meibomian glands combined with eyelid scrubs and warm compresses can provide clinical benefits without serious adverse events. [ABSTRACT FROM AUTHOR]