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Topic:Comparative Study

Comparative studies in equine research involve the systematic analysis of different horse breeds, management practices, or physiological responses to identify variations and similarities. These studies are instrumental in understanding how different factors influence health, performance, and behavior in horses. Common areas of comparison include genetic traits, nutritional requirements, disease resistance, and response to training. By evaluating these differences, researchers can develop targeted strategies for breeding, healthcare, and training. This page aggregates peer-reviewed research studies and scholarly articles that focus on the methodologies, findings, and implications of comparative studies in the context of equine science.
Diagnostic accuracy of digital photography and image analysis for the measurement of foot conformation in the horse.
Equine veterinary journal    January 24, 2009   Volume 40, Issue 7 623-628 doi: 10.2746/042516408x313625
White JM, Mellor DJ, Duz M, Lischer CJ, Voute LC.Rigorous evaluation of practicable methods for the objective assessment of foot conformation has not been performed. Objective: To assess the practicability, precision and accuracy of the process of obtaining measurements of horses' feet using photography and image processing software. Methods: Precision study: Lateral photographs of horses' feet were obtained twice by 2 veterinary surgeons (image acquisition - IAc). Photographs were analysed by 2 masked veterinary surgeons on 2 occasions (image analysis - IAn). Measurements were compared within and between operators for self and non-self acqu...
Influence of time of day on body temperature, heart rate, arterial pressure, and other biological variables in horses during incremental exercise.
Chronobiology international    January 15, 2009   Volume 26, Issue 1 47-60 doi: 10.1080/07420520802689772
Piccione G, Giannetto C, Assenza A, Casella S, Caola G.We examined the response to exercise of selected physiological variables in horses performing the identical routine for eight days, in the morning (a.m.) or in the afternoon (p.m.). Heart rate (HR), systolic and diastolic blood pressure (BP), and body temperature (BT) were all consistently greater in the p.m. For BP and BT, the absolute increase above the a.m. values was the same at rest and during exercise. For HR, the absolute increase was greater during exercise, but the percent increase was the same as during rest. During exercise, blood glucose decreased, while blood lactate and skin temp...
Quantitative and qualitative evaluation of dermal elastin of draught horses with chronic progressive lymphoedema.
Journal of comparative pathology    January 14, 2009   Volume 140, Issue 2-3 132-139 doi: 10.1016/j.jcpa.2008.10.009
De Cock HE, Van Brantegem L, Affolter VK, Oosterlinck M, Ferraro GL, Ducatelle R.Chronic progressive lymphoedema (CPL) in horses, a disease of certain draught breeds, is associated with altered elastin metabolism. The characteristic lesions are seen in the skin of the lower (distal) limbs. This study was based on horses of susceptible breeds, with and without CPL, and on horses of a non-susceptible breed. Skin samples were obtained for examination from the neck (considered a non-affected region) and from the distal limb. The skin lesions were characterized histologically and the dermal elastic fibres were evaluated morphologically and quantitatively. In all horses the mean...
Biomechanical comparison of six suture configurations using a large diameter polyester prosthesis in the muscular process of the equine arytenoid cartilage.
Veterinary surgery : VS    January 13, 2009   Volume 37, Issue 6 580-587 doi: 10.1111/j.1532-950X.2008.00423.x
Kelly JR, Carmalt J, Hendrick S, Wilson DG, Shoemaker R.To compare biomechanical properties of 6 suture configurations using a large diameter polyester prosthesis in the muscular process (MP) of the arytenoid cartilage and to determine failure mode. Methods: Experimental study. Methods: Cadaveric equine larynges (n=121). Methods: Suture configurations (4 single, 2 double) were inserted, and then constructs were tested in a single-cycle to failure at a 100 mm/min distraction. Load deformation curves were generated to assess the biomechanical properties of each construct. A 1-way ANOVA was used to compare the mean differences in construct failure for...
Mineral absorption in tapirs (Tapirus spp.) as compared to the domestic horse.
Journal of animal physiology and animal nutrition    January 13, 2009   Volume 93, Issue 6 768-776 doi: 10.1111/j.1439-0396.2008.00865.x
Clauss M, Lang-Deuerling S, Kienzle E, Medici EP, Hummel J.To test whether mineral recommendations for horses are likely to guarantee adequate mineral provision for tapirs (Tapirus spp.), we investigated the apparent absorption (aA) of macro and micro-minerals in 18 tapirs from five zoological institutions in a total of 24 feeding trials with total faecal collection. Samples of feeds and faeces were analysed for Ca, P, Mg, Na, K, Fe, Cu and Zn. The resulting aA coefficients and the linear relationships of apparently absorbable dietary mineral content to total dietary mineral content (per 100 g dry matter) were compared with data for domestic horses. W...
Acceleration of second and fourth metatarsal fracture healing with recombinant human bone morphogenetic protein-2/calcium phosphate cement in horses.
Veterinary surgery : VS    January 13, 2009   Volume 37, Issue 7 648-655 doi: 10.1111/j.1532-950X.2008.00431.x
Perrier M, Lu Y, Nemke B, Kobayashi H, Peterson A, Markel M.To compare the efficacy of recombinant human bone morphogenetic protein-2 (rhBMP-2)/calcium phosphate (CP) to autogenous cancellous bone graft (CBG) and to no treatment on bone healing, in surgically induced osteotomies and ostectomies of the accessory metatarsal bones in an equine model. Methods: Experimental. Methods: Adult horses (n=9). Methods: Segmental ostectomies of the second metatarsal bone (MT2) and osteotomies of the fourth metatarsal bone (MT4) were performed bilaterally in 9 horses. There were a total of 35 defects (1 MT4 was previously fractured) created and supplemented randomly...
Effect of head position on radiographic assessment of laryngeal tie-forward procedure in horses.
Veterinary surgery : VS    January 13, 2009   Volume 37, Issue 7 608-612 doi: 10.1111/j.1532-950X.2008.00425.x
McCluskie LK, Franklin SH, Lane JG, Tremaine WH, Allen KJ.To assess the effect of head position on relative position of the larynx and hyoid apparatus in horses with palatal dysfunction, and to define a standard position for radiographic assessment of laryngeal tie-forward. Methods: Prospective clinical study. Methods: Adult horses (n=9) with palatal dysfunction. Methods: Left lateral radiographs of the larynx were obtained pre and postoperatively for 3 different head positions (flexed=90 degrees ; neutral=100 degrees ; extended=115 degrees ). Distance between thyrohyoid bone and thyroid cartilage was measured. Data were analyzed to investigate diffe...
Ovulation, pregnancy rate and early embryonic development in vernal transitional mares treated with equine- or porcine-FSH.
Reproduction in domestic animals = Zuchthygiene    January 8, 2009   Volume 45, Issue 2 287-294 doi: 10.1111/j.1439-0531.2008.01296.x
Raz T, Amorim MD, Stover BC, Card CE.The objective of this study was to compare the efficacy of purified equine- and porcine-FSH treatment regimes in mares in early vernal transition. Mares (n = 22) kept under ambient light were examined ultrasonographically per-rectum, starting January 30th. They were assigned to one of two treatment groups using a sequential alternating treatment design when a follicle >or= 25 mm was detected. In the eFSH group, mares were treated twice daily with equine-FSH, and in the pFSH group mares were treated twice daily with porcine-FSH; treatments were continued until follicle(s) >or= 35 mm, and 24 h l...
Differential place and response learning in horses displaying an oral stereotypy.
Behavioural brain research    January 8, 2009   Volume 200, Issue 1 100-105 doi: 10.1016/j.bbr.2008.12.033
Parker M, McBride SD, Redhead ES, Goodwin D.Significant similarities exist between the neural and behavioural features of environmentally and drug-induced stereotypy. For example, exposure to dopamine agonists, such as amphetamine, induces stereotypy and causes alterations in midbrain neurophysiology similar to those observed following chronic stress. An additional behavioural feature of these neural changes in the drug-induced phenotype is an enhanced rate of switching from response-outcome (R-O) to stimulus-response (S-R) learning. The aim of the current experiment was to examine R-O and S-R learning in horses displaying environmental...
Protein expression profile of Gasterophilus intestinalis larvae causing horse gastric myiasis and characterization of horse immune reaction.
Parasites & vectors    January 8, 2009   Volume 2, Issue 1 6 doi: 10.1186/1756-3305-2-6
Roelfstra L, Deeg CA, Hauck SM, Buse C, Membrez M, Betschart B, Pfister K.Little information is available on the immunological aspect of parasitic Gasterophilus intestinalis (Diptera, Oestridae) larvae causing horse gastric myiasis. The objectives of this research were to analyze the protein content of larval crude extracts of the migrating second and third larvae (L2 and L3) of G. intestinalis in order to characterize the immune response of horses. Results: The proteomic profile of L2 and L3, investigated by using one and two dimensional approaches, revealed a migration pattern specific to each larval stage. Furthermore, Western blots were performed with horse sera...
A comparison of epidural buprenorphine plus detomidine with morphine plus detomidine in horses undergoing bilateral stifle arthroscopy.
Veterinary anaesthesia and analgesia    January 6, 2009   Volume 36, Issue 1 67-76 doi: 10.1111/j.1467-2995.2008.00422.x
Fischer BL, Ludders JW, Asakawa M, Fortier LA, Fubini SL, Nixon AJ, Radcliffe RM, Erb HN.To compare the analgesic efficacy of buprenorphine plus detomidine with that of morphine plus detomidine when administered epidurally in horses undergoing bilateral stifle arthroscopy. Methods: Prospective, randomized, blinded clinical trial. Methods: Twelve healthy adult horses participating in an orthopedic research study. Group M (n = 6) received morphine (0.2 mg kg(-1)) and detomidine (0.15 mg kg(-1)) epidurally; group B (n = 6) received buprenorphine (0.005 mg kg(-1)) and detomidine (0.15 mg kg(-1)) epidurally. Methods: Horses received one of two epidural treatments following induction of...
Baseline plasma cortisol and ACTH concentrations and response to low-dose ACTH stimulation testing in ill foals.
Journal of the American Veterinary Medical Association    January 6, 2009   Volume 234, Issue 1 126-132 doi: 10.2460/javma.234.1.126
Wong DM, Vo DT, Alcott CJ, Peterson AD, Sponseller BA, Hsu WH.To evaluate baseline plasma cortisol and ACTH concentrations and responses to low-dose ACTH stimulation testing in ill foals. Methods: Cross-sectional study. Methods: 58 ill foals. Methods: Baseline cortisol and ACTH concentrations and cortisol concentrations after administration of a low dose of cosyntropin were determined within 6 hours after admission. Foals were assigned to 4 groups on the basis of age (<or=24 hours vs 1 to 56 days) and presence of septicemia (yes vs no). Values were compared among groups and with values previously reported for healthy foals. Results: Plasma cortisol co...
Evaluation of allele frequencies of inherited disease genes in subgroups of American Quarter Horses.
Journal of the American Veterinary Medical Association    January 6, 2009   Volume 234, Issue 1 120-125 doi: 10.2460/javma.234.1.120
Tryon RC, Penedo MC, McCue ME, Valberg SJ, Mickelson JR, Famula TR, Wagner ML, Jackson M, Hamilton MJ, Nooteboom S, Bannasch DL.To estimate allele frequencies of the hyperkalaemic periodic paralysis (HYPP), lethal white foal syndrome (LWFS), glycogen branching enzyme deficiency (GBED), hereditary equine regional dermal asthenia (HERDA), and type 1 polysaccharide storage myopathy (PSSM) genes in elite performance subgroups of American Quarter Horses (AQHs). Methods: Prospective genetic survey. Methods: 651 elite performance AQHs, 200 control AQHs, and 180 control American Paint Horses (APHs). Methods: Elite performance AQHs successful in 7 competitive disciplines (barrel racing, cutting, halter, racing, reining, western...
Comparison of chondrogenic potential in equine mesenchymal stromal cells derived from adipose tissue and bone marrow.
Veterinary surgery : VS    January 6, 2009   Volume 37, Issue 8 713-724 doi: 10.1111/j.1532-950X.2008.00462.x
Vidal MA, Robinson SO, Lopez MJ, Paulsen DB, Borkhsenious O, Johnson JR, Moore RM, Gimble JM.To compare the chondrogenic potential of adult equine mesenchymal stem cells derived from bone marrow (MSCs) or adipose tissue (ASCs). Methods: In vitro experimental study. Methods: Adult Thoroughbred horses (n=11). Methods: BM (5 horses; mean [+/-SD] age, 4+/-1.4 years) or adipose tissue (6 horses; mean age, 3.5+/-1.1 years) samples were obtained. Cryopreserved MSCs and ASCs were used for pellet cultures in stromal medium (C) or induced into chondrogenesis+/-transforming growth factor-3 (TGFbeta(3)) and bone morphogenic factor-6 (BMP-6). Pellets harvested after 3, 7, 14, and 21 days were exam...
Genetic diversity of a large set of horse breeds raised in France assessed by microsatellite polymorphism.
Genetics, selection, evolution : GSE    January 5, 2009   Volume 41, Issue 1 5 doi: 10.1186/1297-9686-41-5
Leroy G, Callède L, Verrier E, Mériaux JC, Ricard A, Danchin-Burge C, Rognon X.The genetic diversity and structure of horses raised in France were investigated using 11 microsatellite markers and 1679 animals belonging to 34 breeds. Between-breed differences explained about ten per cent of the total genetic diversity (Fst = 0.099). Values of expected heterozygosity ranged from 0.43 to 0.79 depending on the breed. According to genetic relationships, multivariate and structure analyses, breeds could be classified into four genetic differentiated groups: warm-blooded, draught, Nordic and pony breeds. Using complementary maximisation of diversity and aggregate diversity appr...
Concepts for the clinical use of stem cells in equine medicine.
The Canadian veterinary journal = La revue veterinaire canadienne    January 3, 2009   Volume 49, Issue 10 1009-1017 
Koch TG, Berg LC, Betts DH.Stem cells from various tissues hold great promise for their therapeutic use in horses, but so far efficacy or proof-of-principle has not been established. The basic characteristics and properties of various equine stem cells remain largely unknown, despite their increasingly widespread experimental and empirical commercial use. A better understanding of equine stem cell biology and concepts is needed in order to develop and evaluate rational clinical applications in the horse. Controlled, well-designed studies of the basic biologic characteristics and properties of these cells are needed to m...
Morphology of the occlusal surface for premolar and molar teeth as an indicator of age in the horse.
Journal of veterinary dentistry    January 1, 2009   Volume 26, Issue 4 210-211 
Scrutchfield WL.No abstract available
Measurement of the Curve of Spee in horses.
Journal of veterinary dentistry    January 1, 2009   Volume 26, Issue 4 216-218 doi: 10.1177/089875640902600408
Huthmann S, Staszyk C, Jacob HG, Rohn K, Gasse H.The Curve of Spee is well known, yet hardly understood in the horse, as there is a striking lack of biometrically related data which could help to explain its biomechanical significance. Older horses display drastic alterations of the Curve of Spee in routine clinical examinations. Since the Curve of Spee is known to be biomechanically related to the masticatory forces in humans, the same may apply to the equine, and masticatory deficits can be expected in the geriatric horse. Quantitative data of the Curve of Spee cannot be obtained directly by means of measurements in the horse's long and na...
Administration of sulpiride or domperidone for advancing the first ovulation in deep anestrous mares.
Theriogenology    December 30, 2008   Volume 71, Issue 6 959-965 doi: 10.1016/j.theriogenology.2008.11.001
Mari G, Morganti M, Merlo B, Castagnetti C, Parmeggiani F, Govoni N, Galeati G, Tamanini C.Since results with using sulpiride and domperidone are conflicting and since both have not been tested at the same time, the aim of this study was to compare the efficacy of these substances for the induction of ovulation in deep anestrous mares in the same experimental conditions and to determine their fertility after artificial insemination (AI) at the induced estrus. Twenty-six non-pregnant, non-lactating standardbred anestrous mares were randomly assigned to three groups and treated daily for 25 days (from February 3rd to February 28th) with either sulpiride (1mg/kg of body weight im SID, ...
Serologic response to West Nile virus vaccination in the greater one-horned rhinoceros (Rhinoceros unicornis).
Journal of zoo and wildlife medicine : official publication of the American Association of Zoo Veterinarians    December 30, 2008   Volume 39, Issue 4 537-541 doi: 10.1638/2006-0041.1
Wolf TM, Gandolf AR, Dooley JL, Atkinson MW, Wolfe BA.Vaccination has been an important component of preventative health care programs of North American zoologic institutions in their protection of valuable species against West Nile virus (WNV) infection since its detection in 1999. Although approved only for horses, commercial WNV vaccine has been used for the purpose of protection of nondomestic species, including avian, equid, and rhinoceros species. Currently, there are two commercial equine vaccines available, a killed vaccine and a recombinant viral-vectored vaccine. Both products have been used for the vaccination of Greater One-horned rhi...
Comparison of Montanide adjuvants, IMS 3012 (Nanoparticle), ISA 206 and ISA 35 (Emulsion based) along with incomplete Freund’s adjuvant for hyperimmunization of equines used for production of polyvalent snake antivenom.
Vaccine    December 25, 2008   Volume 27, Issue 7 1067-1072 doi: 10.1016/j.vaccine.2008.11.103
Waghmare A, Deopurkar RL, Salvi N, Khadilkar M, Kalolikar M, Gade SK.The use of adjuvant is of fundamental importance in vaccines formulations and antisera production. Currently selection and use of adjuvant systems in snake antivenom preparation has become a major issue in terms of animal welfare as well as economics. In order to minimize disadvantages associated with traditionally used Freund's adjuvant (FA) in equines and to produce potent polyvalent antivenom against four Indian snake venoms in minimum possible period, a comparison was made between various commercially available non-emulsion/emulsion based adjuvants like IMS 3012, ISA 206 and ISA 35 with In...
Isolation and characterization of the equine influenza virus causing the 2006 outbreak in Chile.
Veterinary microbiology    December 24, 2008   Volume 137, Issue 1-2 172-177 doi: 10.1016/j.vetmic.2008.12.011
Müller I, Pinto E, Santibáñez MC, Celedón MO, Valenzuela PD.The equine influenza virus is the causal agent of influenza in horses. In July 2006, horses from various regions of Chile presented fever, serious nasal discharge, dry cough, anorexia and depression. Here we describe the isolation and characterization of the virus responsible for this outbreak. The virus was identified as equine influenza virus H3N8, since haemagglutination was inhibited by an anti-A/equi/1/H3N8 serum, but not by an anti-A/equi/1/H7N7 serum. The isolate was named A/equi/2/Lonquén/06 (H3N8). In addition, we describe the isolation and sequencing of the haemagglutinin, neuramini...
Comparative molecular analysis substantiates zoonotic potential of equine methicillin-resistant Staphylococcus aureus.
Journal of clinical microbiology    December 24, 2008   Volume 47, Issue 3 704-710 doi: 10.1128/JCM.01626-08
Walther B, Monecke S, Ruscher C, Friedrich AW, Ehricht R, Slickers P, Soba A, Wleklinski CG, Wieler LH, Lübke-Becker A.Despite the increasing importance of methicillin-resistant Staphylococcus aureus (MRSA) in veterinary medicine, knowledge about the epidemiology of the pathogen in horses is still poor. The phylogenetic relationship of strains of human and equine origins has been addressed before, usually by analyzing results of common standard classification methods for MRSA. This work intends to go beyond the baseline of typing procedures in order to comparatively characterize equine and human MRSA strains with similar phylogenetic backgrounds. In addition to multilocus sequence typing, pulsed-field gel elec...
Effects of trunk deformation on trunk center of mass mechanical energy estimates in the moving horse, Equus caballus.
Journal of biomechanics    December 23, 2008   Volume 42, Issue 3 308-311 doi: 10.1016/j.jbiomech.2008.11.005
Nauwelaerts S, Kaiser L, Malinowski R, Clayton HM.The estimation of the position of the center of mass (CM) is essential in a wide range of biomechanical analyses. In horses, the majority of the body mass is contained in the trunk and in most studies, the trunk is assumed to be rigid. However, this rigidity assumption has not been tested. We quantified changes in the position of the trunk CM due to external shape changes by measuring the kinematics of a mesh encompassing the trunk. Using a frame of reference fixed to the horse's spine, we described the shape deformation of the trunk during walking. In addition, we tested for speed and individ...
The activity and expression of chitinase in the equine lung and its activity in normal horses and animals with recurrent airway obstruction.
Research in veterinary science    December 21, 2008   Volume 87, Issue 1 20-25 doi: 10.1016/j.rvsc.2008.11.002
Reid CJ, Thompson L, Donnelly S, Deaton CM, Marlin DJ, Carrington SD, Irwin JA.Recurrent airway obstruction (RAO) is a chronic inflammatory condition in equine lung, which may share a common immunological basis with human asthma, in which dysregulated Th2 responses occur. Mammals express chitinases and chitinase-like proteins, two of which are active enzymes, chitotriosidase and acidic mammalian chitinase (AMCase). Both enzymes are upregulated in a range of inflammatory conditions, including asthma. We investigated the activity of chitinase in bronchoalveolar lavage fluid from horses with and without RAO in response to organic dust challenges. No significant differences ...
Exercise-induced metacarpophalangeal joint adaptation in the Thoroughbred racehorse.
Journal of anatomy    December 20, 2008   Volume 213, Issue 6 706-717 doi: 10.1111/j.1469-7580.2008.00996.x
Muir P, Peterson AL, Sample SJ, Scollay MC, Markel MD, Kalscheur VL.Repetitive bone injury and development of stress fracture is a common problem in humans and animals. The Thoroughbred racehorse is a model in which adaptive failure and associated development of stress fracture is common. We performed a histologic study of the distal end of the third metacarpal bone in two groups of horses: young Thoroughbreds that were actively racing (n = 10) and a group of non-athletic horses (n = 8). The purpose of this study was to determine whether development of articular microcracks was associated with specific alterations to subchondral plate osteocytes. Morphometric ...
Virtual histology by means of high-resolution X-ray CT.
Journal of microscopy    December 20, 2008   Volume 232, Issue 3 476-485 doi: 10.1111/j.1365-2818.2008.02142.x
Cnudde V, Masschaele B, De Cock HE, Olstad K, Vlaminck L, Vlassenbroeck J, Dierick M, Witte YD, Van Hoorebeke L, Jacobs P.Micro-CT is a non-destructive technique for 3D tomographic investigation of an object. A 3D representation of the internal structure is calculated based on a series of X-ray radiographs taken from different angles. The spatial resolution of current laboratory-used micro-CT systems has come down over the last years from a few tens of microns to a few microns. This opens the possibility to perform histological investigations in 3D on a virtual representation of a sample, referred to as virtual 3D histology. The advantage of micro-CT based virtual histology is the immediate and automated 3D visua...
Blindness, optic atrophy and sinusitis in the horse.
Veterinary ophthalmology    December 17, 2008   Volume 11 Suppl 1 20-26 doi: 10.1111/j.1463-5224.2008.00642.x
Barnett KC, Blunden AS, Dyson SJ, Whitwell KE, Carson D, Murray R.The case histories described each presented with a visual deficit, varying from permanent total blindness with ophthalmoscopic evidence of optic atrophy to variable and transient visual disturbances, including occasional blindness, but with absence of ophthalmoscopic or any other ocular abnormality. Methods: Three horses of widely different age and type, but all with an original history of upper respiratory tract infection. Methods: All three cases were examined by a specialist veterinary ophthalmologist. In addition, magnetic resonance imaging (MRI) and, where possible, postmortem and histopa...
An overview of recent developments in corneal immunobiology: potential relevance in the etiogenesis of corneal disease in the horse.
Veterinary ophthalmology    December 17, 2008   Volume 11 Suppl 1 66-76 doi: 10.1111/j.1463-5224.2008.00635.x
Matthews AG.This paper overviews some recent developments in mammalian corneal immunobiology, and discusses how these may act as pointers towards understanding the immunology underlying some common corneal diseases in the horse, including infectious ulceration and presumptively immune-mediated non-ulcerative disease. Specifically, three aspects of corneal immunobiology are examined: the role of Toll-like receptors in surface immunity and in the etiogenesis of microbial ulceration, the relationship between conjunctiva associated lymphoid tissue (CALT) and immunoprotection of the corneal surface, and the me...
Daily rhythm of tear production in normal horse.
Veterinary ophthalmology    December 17, 2008   Volume 11 Suppl 1 57-60 doi: 10.1111/j.1463-5224.2008.00647.x
Piccione G, Giannetto C, Fazio F, Giudice E.This study was designed to assess the daily rhythm of tear production in clinically healthy horses, to compare left eye and right eye, and to evaluate the influence of time and gender. Methods: For our study 18 horses (nine female and nine male) were subjected to three different light/dark (L/D) schedules: 12/12 L/D cycles, constant light (24/0 L/D) and constant darkness (0/24 L/D). Methods: In all subjects Schirmer tear tests were performed at 4-h intervals over a 24-h period. Results: A circadian rhythm of tear production was found during the 12/12 L/D period and during constant darkness. Al...