How eyelashes can protect the eye through inhibiting ocular water evaporation: a chemical engineering perspective.

Bionics is a fascinating subject that has inspired many inventions through learning from biological structures and functions. In this work, a coupled multi-physics model has been developed to characterize ocular water evaporation with realistic eyelash structures taken into account. From a chemical engineering perspective, the protective function of human eyelashes in terms of evaporation inhibition has been rationally revealed. Systematic investigations were carried out to elucidate the effects of different eyelash lengths, orientations and inlet air directions on water evaporation on the ocular surface. The results clearly demonstrate that regardless of inlet air directions and eyelash orientations, increasing eyelash length from zero to an optimal length can effectively reduce water evaporation. However, further increase in the eyelash length can lead to enhanced evaporation. For the normal and parallel inlet air directions, the optimal eyelash length is around 15-30% of the eye width and can offer approximately 10-30% evaporation reduction when compared with the cases without eyelashes. These values are independent of the eyelash orientation. This investigation provides valuable data for in-depth understanding of the protective function of the eyelashes, which can be used in the future to improve and optimize bionic designs inspired by human eyelashes.

The eyelash follicle features and anomalies: A review / Características y anomalías del folículo de la pestaña: revisión

The primary role of eyelashes is to protect and maintain the health of the lid margin. However, the mechanisms to fulfill this role are not fully understood. Unraveling these mechanisms will stand to greatly improve the efficiency of eye care professionals’ interventions in anomalies of the eyelashes. The aim of this article is to provide a review on eyelashes including highlights and new avenues for research; the biology of both the lash and its follicle; the pathophysiology and management of lash anomalies by eye care professionals; and the effect of iatrogenic factors on lashes. Using the database of Ovid MEDLINE, we reviewed studies specifically directed on human/mammalian eyelashes and key articles on current trends in scalp hair methodologies that can be applicable to lash research. The eyelash morphology, pigmentation and growth rate have been documented using techniques ranging from lash imaging to follicle immunohistochemistry. Furthermore, studies have demonstrated that the lash follicle is sensitive to many factors of the external environment, a variety of systemic/topical medications and cosmetics. Recently, aerodynamic studies using a mammalian eye model confirmed that an optimal lash length was needed so that eyelashes serve a protective role in reducing the number of particles that can reach the eye. Despite recent advances in lash research, studies are still scarce, due to the limited availability of the human lid for sampling. This review brings awareness that further research is needed with respect to eyelashes and will hopefully reduce the gap with scalp hair research

La función principal de las pestañas es proteger y mantener la salud del margen palpebral. Sin embargo, los mecanismos de desempeño de esta función no se comprenden plenamente. Desentrañar estos mecanismos ayudará a mejorar la eficiencia de las intervenciones de los profesionales de cuidados oculares en cuanto a las anomalías de las pestañas. El objetivo de este artículo es aportar una revisión sobre las pestañas, incluyendo los aspectos más destacados y las nuevas aportaciones para la investigación, la biología de la pestaña y su folículo, la patofisiología y tratamiento de las anomalías de las pestañas por parte de los profesionales de cuidados oculares, y el efecto de los factores iatrogénicos sobre las pestañas. Utilizando la base de datos de Ovid MEDLINE, revisamos los estudios específicamente dirigidos a las pestañas humanas/de mamíferos, así como los artículos clave sobre las tendencias actuales en cuanto a las metodologías del cuero cabelludo, que pueden aplicarse a la investigación sobre las pestañas. Se han documentado la morfología de las pestañas, así como su pigmentación y tasa de crecimiento, utilizando técnicas que oscilan entre la imagen de las pestañas y la inmunohistoquímica del folículo. Además, los estudios han demostrado que el folículo de la pestaña es sensible a diversos factores del entorno externo, diversas medicaciones sistémicas/tópicas y cosméticos. Recientemente, los estudios aerodinámicos que han utilizando un modelo de ojo de mamífero, han confirmado que se precisaba una longitud de pestañas óptima para que éstas ejercieran su función protectora a la hora de reducir el número de partículas que pueden acceder al ojo. A pesar de los avances recientes de la investigación sobre las pestañas, los estudios son aún escasos, debido a la disponibilidad limitada de párpado humano para muestreo. Esta revisión sirve de concienciación acerca de la necesidad de investigación futura con respecto a las pestañas, que reducirá presumiblemente la brecha existente con respecto a la investigación sobre el cuero cabelludo

The eyelash follicle features and anomalies: A review.

The primary role of eyelashes is to protect and maintain the health of the lid margin. However, the mechanisms to fulfill this role are not fully understood. Unraveling these mechanisms will stand to greatly improve the efficiency of eye care professionals' interventions in anomalies of the eyelashes. The aim of this article is to provide a review on eyelashes including highlights and new avenues for research; the biology of both the lash and its follicle; the pathophysiology and management of lash anomalies by eye care professionals; and the effect of iatrogenic factors on lashes. Using the database of Ovid MEDLINE, we reviewed studies specifically directed on human/mammalian eyelashes and key articles on current trends in scalp hair methodologies that can be applicable to lash research. The eyelash morphology, pigmentation and growth rate have been documented using techniques ranging from lash imaging to follicle immunohistochemistry. Furthermore, studies have demonstrated that the lash follicle is sensitive to many factors of the external environment, a variety of systemic/topical medications and cosmetics. Recently, aerodynamic studies using a mammalian eye model confirmed that an optimal lash length was needed so that eyelashes serve a protective role in reducing the number of particles that can reach the eye. Despite recent advances in lash research, studies are still scarce, due to the limited availability of the human lid for sampling. This review brings awareness that further research is needed with respect to eyelashes and will hopefully reduce the gap with scalp hair research.

Effects of LATISSE (bimatoprost 0.03 per cent topical solution) on the ocular surface.

PURPOSE: LATISSE is marketed for the treatment of hypotrichosis (loss of eyelashes), using a prostamide analogue and preserved with benzalkonium chloride, which is an effective preservative; however, it also causes irritation to the ocular surface. LATISSE is applied to the lid margin; however, with the blink, some solution may fall onto the ocular surface. The objective of this study was to assess the effects of LATISSE on the ocular surface over two months. METHODS: Non-dry eye participants interested in eyelash lengthening were invited to a prospective uncontrolled, open-label clinical study using LATISSE for two months. Eyelash length, subjective symptoms, tear film stability, osmolarity, ocular redness and intraocular pressure were evaluated at baseline (T0) and at one (T1) and two months (T2). RESULTS: Twenty-eight women (ages 18 to 29) entered the study. Fifteen completed the study with five who discontinued due to burning upon instillation and eight were lost to follow-up. Average eyelash length increased at each time (p < 0.001). Dryness, burning and grittiness remained low (less than 25/100) throughout the trial with dryness showing a significant change between T0 and T1 (p = 0.04), but not between T1 and T2 (p > 0.05). No difference (p > 0.05) was noted for the non-invasive break-up time, photochromametry or tear osmolarity. Intraocular pressure showed a decrease with time but translated to only a one to two mmHg change, which was not clinically relevant. CONCLUSIONS: LATISSE increases eyelash length within a short time (less than two months). Patients seeking eyelash enhancement options should be educated as to the use, precautions and any secondary effects, including the potential for discomfort upon instillation.

Biology of the eyelash hair follicle: an enigma in plain sight.

Because of their crucial impact on our perception of beauty, eyelashes constitute a prime target for the cosmetic industry. However, when compared with other hair shafts and the mini-organs that produce them [eyelash hair follicles (ELHFs)], knowledge on the biology underlying growth and pigmentation of eyelashes is still rudimentary. This is due in part to the extremely restricted availability of human ELHFs for experimental study, underappreciation of their important sensory and protective functions and insufficient interest in understanding why they are distinct from scalp hair follicles (HFs) (e.g. ELHFs produce shorter hair shafts, do not possess an arrector pili muscle, have a shorter hair cycle and undergo greying significantly later than scalp HFs). Here we synthesize the limited current knowledge on the biology of ELHFs, in humans and other species, their role in health and disease, the known similarities with and differences from other HF populations, and their intrinsic interethnic variations. We define major open questions in the biology of these intriguing mini-organs and conclude by proposing future research directions. These include dissecting the molecular and cellular mechanisms that underlie trichomegaly and the development of in vitro models in order to interrogate the distinct molecular controls of ELHF growth, cycling and pigmentation and to probe novel strategies for the therapeutic and cosmetic manipulation of ELHFs beyond prostaglandin receptor stimulation.

Nuevas teorías sobre la función de las pestañas. ¿Una cuarta capa en la película lacrimal? / New theories on the role of the eyelashes. A fourth layer in the tear film?

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Management of hypotrichosis of the eyelashes: focus on bimatoprost.

Prominent eyelashes are generally recognized as enhancing beauty and are often desired by women. Until recently, the options available to augment the prominence of eyelashes were limited to makeup, over-the-counter products, artificial eyelashes, and eyelash transplantation. Originally approved for the treatment of ocular hypertension, the prostamide, bimatoprost, is now approved for the treatment of hypotrichosis of the eyelashes. Bimatoprost ophthalmic solution 0.03%, applied once daily to the skin of the upper eyelid margin using sterile single-use-per-eye applicators, increases eyelash growth, including length, thickness, and darkness. The effectiveness of bimatoprost for eyelash growth has been demonstrated by clinician ratings, digital image analysis, and patient-reported measures of satisfaction. The effects of bimatoprost treatment on eyelash length, thickness, and darkness are believed to result from longer anagen duration, increased hair bulb thickness, and increased melanogenesis, respectively. Dermally applied bimatoprost appears to be associated with a lower incidence of adverse events than administration of the medication as an eyedrop. This more favorable safety and tolerability profile is likely mediated by decreased exposure of ocular tissues to bimatoprost when applied dermally. Taken together, available data suggest that cutaneous application of bimatoprost ophthalmic solution 0.03% safely and effectively enhances upper eyelash growth.

Eyelashes divert airflow to protect the eye.

Eyelashes are ubiquitous, although their function has long remained a mystery. In this study, we elucidate the aerodynamic benefits of eyelashes. Through anatomical measurements, we find that 22 species of mammals possess eyelashes of a length one-third the eye width. Wind tunnel experiments confirm that this optimal eyelash length reduces both deposition of airborne particles and evaporation of the tear film by a factor of two. Using scaling theory, we find this optimum arises because of the incoming flow's interactions with both the eye and eyelashes. Short eyelashes create a stagnation zone above the ocular surface that thickens the boundary layer, causing shear stress to decrease with increasing eyelash length. Long eyelashes channel flow towards the ocular surface, causing shear stress to increase with increasing eyelash length. These competing effects result in a minimum shear stress for intermediate eyelash lengths. This design may be employed in creating eyelash-inspired protection for optical sensors.

Age estimation using level of eyebrow and eyelash whitening.

BACKGROUND: The aim of this study was to determine whether eyebrow and eyelash whitening is an effective parameter in age estimation. MATERIAL AND METHODS: We evaluated 1545 patients. Age groups were 1-10, 11-20, 21-30, 31-40, 41-50, 51-60, 61-70, 71-80, and 81-90 years. Level of whitening was categorized as level 0: no whitening, level 1: 1-3 strands, level 2: 3-10 strands, level 3: 10 strands-2/3 whitening, level 4: >3/4 whitening. RESULTS: Mean age was 42.39 ± 20.01. While there was no eyebrow whitening in 87% of the subjects, level 4 whitening of eyebrows was observed in 0,8% of the subjects. There was no eyelash whitening in 97,7% of the subjects and no level 4 eyelash whitening was detected in any subject. Men had significantly more level 1, 2, 3, and 4 eyebrow whitening compared with women. There was no gender difference in terms of eyelash whitening level. There was no eyebrow and eyelash whitening in subjects age 1-40 years; whitening began in the 41-50 years age group and increased with age in other groups. Mean age was 39.59 ± 19.63 years in subjects with no eyebrow whitening; 59 years in level 1, 61 years in level 2, 63 years in level 3, and 69 years in level 4 eyebrow whitening. Mean age was 41.85 ± 19.87 in subjects with no eyelash whitening; and 63.57 ± 10.75 in those with whitening. CONCLUSIONS: Particularly after 41-50 years of age, level of eyebrow and eyelash whitening may be among a useful age estimation parameter.

Eyebrow composite graft for eyelash reconstruction: a case report and review of the literature.

Reconstructing the eyelash margin is a challenge for plastic surgeons because eyelashes have specific characteristics. There is still no gold standard procedure for this type of reconstruction, which seeks to protect the eyeball and make the eyelid appear natural. The eyebrow composite graft can be a good option for reconstructing the eyelash margin because it is technically simple and safe, and takes advantage of the structural similarity between the eyelashes and eyebrow. The results presented showed the effectiveness of the technique by providing improved occlusion and a good aesthetic result.

The effect of ketamine on clinical endpoints of hypnosis and EEG variables during propofol infusion.

BACKGROUND: We studied the effect of variable doses of ketamine on the endpoints of hypnosis, e.g., unresponsiveness to verbal commands (UVC), loss of eyelash reflex (LER), and inhibition of body movement response with or without sneezing to nasal membrane stimulation (INBMR), and processed EEG variables, e.g., bispectral index (BIS), 95% spectral edge frequency (SEF) and median frequency (MF) during propofol infusion. METHODS: Forty-eight patients received either propofol infusion, 30 mg.kg-1.h-1 (Group P; n = 12) or ketamine bolus, 0.25, 0.5 or 0.75 mg i.v., followed by propofol infusion, 30 mg.kg-1.h-1 + variable dose ketamine infusion, 0.25, 0.5 or 0.75 mg.kg-1.h-1 (Groups PK0.25, PK0.5 and PK0.75; n = 12 each) until UVC, LER and INBMR. BIS, 95% SEF and MF values were monitored and recorded at the endpoints of hypnosis. Propofol and ketamine concentrations were measured at INBMR. RESULTS: Propofol infusion, 30 mg.kg-1.h-1, induced UVC, LER and INBMR at BIS: 65 +/- 2, 63 +/- 9 and 33 +/- 7; 95% SEF: 17 +/- 3, 17 +/- 4 and 14 +/- 3; and MF values of 5 +/- 2, 5 +/- 3 and 3 +/- 2, respectively. With adjunctive ketamine (Groups PK0.5 and PK0.75), the hypnotic endpoints were achieved at higher BIS and 95% SEF values and lower propofol doses and concentrations as compared to Groups P and PK0.25 (9.9 +/- 5.8 and 9.4 +/- 3.4 vs. 13.4 +/- 4.5 and 14 +/- 5.8 micrograms.ml-1). CONCLUSIONS: Our results suggest additive interaction between propofol and ketamine (Groups PK0.5 and PK0.75) for achieving the hypnotic endpoints; however, ketamine did not depress the EEG variables in proportion to its hypnotic effect. The paradoxically higher BIS and 95% SEF values at the hypnotic endpoints may be due to lower propofol concentrations and/or no effect of ketamine on the EEG variables.

Anatomy and physiology of eyelash follicles: relevance to lash ablation procedures.

BACKGROUND: This study aimed to define the anatomy of the eyelash follicles in order to improve methods of selective lash ablation. MATERIALS AND METHODS: Dimensions of eyelash follicles were determined from histological specimens of the upper and lower lids of 10 patients. For one of these patients, the eyelash follicles were categorized as quiescent or actively growing, according to standard hair-cycle morphology. RESULTS: Follicle dimensions were (mean +/- SD): upper lid follicle depth, 1.8 +/- 0.3 mm; bulb width, 188 +/- 44 microns; shaft width, 205 +/- 28 microns; lower lid follicle depth, 0.9 +/- 0.2 mm; bulb width 132 +/- 19 microns; and shaft width, 158 +/- 26 microns. The upper lid comprised 41% active follicles compared to 15% in the lower lid. CONCLUSIONS: There are significant differences in the anatomy of the follicles between the two lids. For an electrolysis needle to completely contact 95% of all follicles, it must be inserted 2.4 mm into the upper lid and 1.4 mm into the lower lid (mean depth +2 SD). Argon laser ablation requires a beam width of < 200 and < 250 microns for the lower and upper lids, respectively, to treated similar depths as electrolysis. The higher proportion of actively growing upper lid follicles explains why upper lid lashes are longer.

Prediction of movement during propofol/nitrous oxide anesthesia. Performance of concentration, electroencephalographic, pupillary, and hemodynamic indicators.

BACKGROUND: Movement in response to painful stimulation is the end point classically used to assess the potency of anesthetic agents. In this study, the ability of modeled propofol effect-site concentration to predict movement in volunteers during propofol/nitrous oxide anesthesia was tested, then it was compared with the predictive abilities of the Bispectral Index and 95% spectral edge frequency of the electroencephalogram, pupillary reflex amplitude, and systolic arterial blood pressure. In addition, the relationships between simple end points of loss and recovery of consciousness, and pupillary, hemodynamic, and propofol concentration indicators were studied. METHODS: Ten healthy volunteers were anesthetized with an infusion of propofol, which was increased in three equal steps to 21 mg.kg lean body mass-1.h-1. After loss of the ability to hold a syringe and of the eyelash reflex, 60% nitrous oxide was introduced and the trachea was intubated without the use of muscle relaxants. The propofol infusion rate then was decreased to 15.4 mg.kg lean body mass-1.h-1. Ten minutes later, tetanic electrical stimulation was administered to the thigh via needle electrodes: if movement was observed within 1 min, the propofol infusion rate was increased by 1.75 mg.kg lean body mass-1.h-1 5 min after the stimulus; if not, it was similarly decreased. This 15-min sequence was repeated until volunteers "crossed over" from movement to no movement (or vice versa) four times. The propofol infusion rate then was increased to 21 mg.kg lean body mass-1.h-1, nitrous oxide was discontinued, the trachea was extubated, and the infusion rate was decreased in five equal steps over 50 min. The times at which the eyelash reflex returned and the birth date was recalled were recorded. The electroencephalogram was monitored continuously (FP1, FP2, ref: nasion, ground: mastoid). Measurements of the pupillary response, arterial blood pressure, and heart rate were recorded during induction and awakening, just before and for 5 min after each stimulation. Arterial blood samples were obtained for propofol assay, and propofol effect-site concentrations were calculated at each time. The predictive value of indicators was compared using a new static, the prediction probability (PK). RESULTS: Loss and return of the eyelash reflex occurred at greater propofol effect-site concentrations than either dropping the syringe or recall of the birthday. The propofol effect-site concentration (in the presence of 60% nitrous oxide) predicted to prevent movement after a supramaximal stimulus in 50% of volunteers was 1.80 micrograms/ml (95% confidence limits: 1.40-2.34 micrograms/ml). The Bispectral Index (PK = 0.86), 95% spectral edge frequency (PK = 0.81), pupillary reflex amplitude (PK = 0.74), and systolic arterial blood pressure (PK = 0.78) did not differ significantly from modeled propofol effect-site concentration (PK = 0.76) in their ability to predict movement. CONCLUSIONS: Indicators of pharmacodynamic effect, such as the electroencephalogram, pupillary light reflex, and systolic arterial blood pressure, predict movement as well as effect-site concentration during propofol/nitrous oxide anesthesia. Loss and return of the eyelash reflex correspond to a deeper level of anesthesia than syringe-dropping or recall of the birth date.

Pharmacodynamics of propofol in female patients.

Although the clinical properties of propofol have been studied extensively, the pharmacodynamics have not yet been described fully. We studied the propofol concentration-effect relationships for loss of eyelash reflex, loss of consciousness, and hemodynamic changes in 18 female patients, ASA physical status 1, aged 20-49 yr. Propofol was given by computer-controlled infusion. The initial target concentration of 0.5-1 microgram/ml was increased every 12 min by 0.5-1 microgram/ml until the patients lost consciousness. Every 3 min, loss of eyelash reflex and loss of consciousness were tested and an arterial blood sample was taken for analysis of the blood propofol concentration. The concentration-response relationships for loss of eyelash reflex and loss of consciousness were defined by fitting a sigmoid Emax function (where Emax = the maximum effect that can be reached; i.e., 100% of the patients showing loss of eyelash reflex or loss of consciousness) to the response/no response data versus the propofol concentration, using nonlinear regression. The effect of propofol on hemodynamic parameters was analyzed by linear regression. The propofol concentrations at which 50% and 90% of the patients showed loss of eyelash reflex were 2.07 and 2.78 micrograms/ml, respectively. The corresponding values for loss of consciousness were 3.40 and 4.34 micrograms/ml. The systolic and diastolic blood pressure decreased with increasing blood propofol concentration. The correlation coefficients for the decrease in systolic and diastolic blood pressure versus the blood propofol concentration were r2 = -0.663 and r2 = -0.243, but heart rate did not change. In conclusion, propofol concentrations inducing loss of eyelash reflex are less than those inducing loss of consciousness.

Induction dose-responses studies with propofol and thiopentone.

The relative potencies of propofol and thiopentone were assessed using different indicators of induction of anaesthesia: abolition of the response to verbal commands and eyelash stimulation. Log-probit dose-response curves for these end-points were determined 30, 60 and 90 s after induction in 96 unpremedicated ASA group I patients. For propofol, ED50 values for abolition of the response to verbal commands and eyelash stimulation at different time intervals were in the ranges 1.16-1.42 and 1.23-1.72 mg kg-1, respectively; corresponding ED95 values were 2.18-2.67 and 2.42-3.27 mg kg-1, respectively. For thiopentone, the calculated ED50 values for verbal commands and eyelash stimulation at the same time intervals were 1.81-2.23 and 3.55-3.40 mg kg-1; corresponding ED95 values were 5.11-6.29 and 6.41-6.70 mg kg-1, respectively. The potency ratio of propofol to thiopentone observed in this study varied from 1:1.27 to 1:2.88. It is concluded that a dose-response curve reflecting one end-point of anaesthesia cannot be used to define another end-point of anaesthesia.

Induction dose-response of propofol in unpremedicated children.

The induction dose requirements of propofol were compared in three age groups in 300 unpremedicated healthy Chinese children: group A, younger than 2 yr (n = 48); group B, 2-5 yr (n = 117); group C, 6-12 yr (n = 135). Patients in each group were allocated randomly to receive one of eight doses of propofol (1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4 and 2.6 mg kg-1). ED50 and ED95 for loss of eyelash reflex (LER) and acceptance of face mask (AFM) were determined using probit analysis. ED50 and ED95 for both LER and AFM were greatest in group A, less in B and smallest in C; ED95 (AFM) for groups A, B and C were 2.88 (2.55-3.36), 2.53 (2.31-2.86), and 2.20 (2.02-2.46) mg kg-1, respectively. This probably represented their effective induction dose. The incidence of apnoea was dose related, but not pain on injection.

Recovery from total intravenous anaesthesia. Propofol versus midazolam-flumazenil.

The aim of this study was to compare recovery assessed with the Newman, deletion af a's and postbox tests after total intravenous anaesthsia for procedures lasting more than 90 min, with either propofol (PPF) or midazolam (MDZ), reversed or not by flumazenil (FMZ). Thirty patients scheduled for peripheral surgery were randomly allocated to 3 groups of 10, receiving by continuous infusion until the end of surgery either PPF (n = 10) or MDZ (n = 20) combined with alfentanil. FMZ was administered thereafter to 10 patients receiving MDZ until they opened their eyes on command or to a maximum dose of 1 mg. Recovery tests were performed 45, 90 and 180 min after the end of anaesthesia. Results were analysed with non-parametric tests. Recovery scores were significantly better in the PPF group at all times, reaching control values at 180 min for the three first tests. FMZ reversal did not improve the scores compared to those resulting from MDZ alone. This study provides further data in favour of PPF as far as rapid and complete recovery is concerned. The efficiency of FMZ is incomplete and only transient when administered in a single dose.

[The lashes. Physiology, structure, pathology (author's transl)]. / Les cils. Physiologie, structure, pathologie.

In spite of the similarity between hairs and eyelashes the later shows several physiological and anatomical particularities. We performed an ultrastructural study of eyelashes and reviewed their pathology.

Cryosurgery for treatment of trichiasis.

We cryosurgically destroyed eyelashes in rabbits and applied the technique to treat 23 selected patients with trichiasis. Liquid nitrogen was sprayed on the eyelid margin by using a double, rapid-freeze, slow-thaw cycle monitored by a subcutaneous thermocouple to -30 degrees C. It was an improvement on electrolysis and a simple alternative to surgery.