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LIVESTOCK RESEARCH INTERNATIONAL
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MINI-REVIEW
Role of Lacrimal Gland in Tear Production in Different Animal Species: A
Review
R. Menakab and Gopal Puri*a
a
Associate Professor, Deptt. Of Veterinary Physiology and Biochemistry, bAssistant Professor, Deptt. of Veterinary
Anatomy, Vanbandhu College of Veterinary Sciences and Animal Husbandry, Navsari Agricultural University,
Navsari- 396 450, India.
*Corresponding Author:
Abstract
Revised: 27/06/2015
The lacrimal gland is a serous acini lobulated gland which have comprised
of cuboidal epithelium. The secretary variations are observed in different domestic
animals. In swine, the secretion is mucous in nature. The cells are showing mucin
reaction in sheep, goat and dog. Lacrimation is one of the physiological events that
protects the eye ball and further prevents the pathogenic infection. There are small
accessory glands which found in the third eyelids and it further contributes
approximately 50 % composition of the tear film. The pre-corneal surface protected
by mucus coating which is secreted by the goblet cells of conjunctival membrane.
Accepted: 28/06/2015
Key words: Lacrimal, Mucin, Tear film, Precorneal, Conjunctival, Acini.
Gopal Puri
Email: [email protected]
Received: 18/06/2015
1. Introduction
The eye is a complex and highly developed
organ which collects light from the surrounding
environment. It regulates its intensity through a
diaphragm, focuses it through an adjustable lens to
form an image on retina where this image is converted
into a set of electrical signals and transmitted to the
brain. The eyes are protected in the skull by a bony box
called the eye socket (orbit). The wall of this eyeball
consists of three layers which have different tasks in
the anterior and posterior halves of the organ (Konig
and Liebich, 2007). One of the accessory structures of
the eye is the lacrimal apparatus which located
superiorly and laterally to each eyeball. Each lacrimal
apparatus consists of the lacrimal gland, canalicule,
lacrimal sac and naso lacrimal duct. The lacrimal gland
is responsible for production and secretion of tears
which clean and nourish the cornea and help to
maintain corneal health. The lacrimal apparatus are
responsible for the production, dispersal and disposal
of the tears.
The lacrimal fluid keeps the anterior surface of
the eyes moist and clean. In addition to salts (NaCl1%), it contains small amount of protein. The lacrimal
secretion also consists of bactericidal enzyme known as
lysozyme which may be considered part of the defense
against infection. The pre-corneal tear film protects the
eyes by washing away foreign material. It is essential
in maintain the transparency of the cornea. Insufficient
tear production results in opacification. The
keratoconjunctivitis sicca (KCS) is a chronic
inflammatory disease due to quantitative or qualitative
abnormalities of the tear film, frequently reported in
dogs. The lacrimal gland can be involved in immunemediated, toxic, infectious, or cancerous processes
(Slatter, 1973; Hirayama et al., 2000 and Vinayak et
al., 2004). The normal volume of tear fluid is about 5–
10µl per day.
2. Lacrimation
Animals do not tear up or cry for emotional
reasons as humans do. Secretion of tears serves to clean
and lubricate the eye in response to an irritation of the
eyes. Tearing can be an indicator of irritation,
inflammation, injury or infection to the eye. Possible
causes of lacrimation in pets are limited to allergy,
physical or chemical irritant, misplaced eyelashes,
eyelid growth, and chemical spill, wound or direct
injury, corneal ulcer, blocked tear ducts, some systemic
diseases or toxin ingestion.
Tear or lacrimation is considered to have a
unique structure with functions of nourishing,
lubricating and protecting the ocular surface,
containing lipid, protein, and mucous components
(Tiffany, 2008; Ohashi et al., 2006). Proteins in the tear
are play an important role in protecting the ocular
surface from the pathogens, maintaining the integrity
and stability of the tear and modulating the ocular
wound healing process (Zhou et al., 2007). The
comprehensive and comparative analysis of tear
proteins can be helpful in the studies of pathophysiological mechanisms and diagnosis of ocular
surface diseases. The healthy ocular surface is
associated with normal tear production and the stability
of the tear film, which are found to be affected by
several endogenous and exogenous factors, such as
Livestock Research International | April-June, 2015 | Vol 3 | Issue 2 | Pages 40-42
© 2015 Jakraya Publications (P) Ltd
Menaka and Puri…Role of Lacrimal Gland in Tear Production in Different Animal Species: A Review
age, gender, the time of day, and environmental
conditions (Piccione et al., 2008).
Studies on humans and animals have reported
the daily variations of tear production. The potential
influence of season has also been evaluated in tear
production of normal horses by Schirmer tear test.
However, no statistically different Schirmer tear test
values were found in winter compared to the respective
values in summer (Beech et al., 2003).
3. Composition of Tear Film
The lacrimal gland (LG) is an epithelial gland
that is responsible for approximately 60% of the
production of the aqueous component of the precorneal tear film with the remaining 40% contributed
by the accessory lacrimal gland of the third eyelid
(Junquira and Carneiro, 2003). The major secretary
sources of protein are to optimize the optics of the
cornea, to lubricate and to protect the eye from the
pathogens. Tear film is made up of tri-laminar structure
7µ thickness which consists of lipid, aqueous and
mucin (Mohamadpour, 2008). The lacrimal film is
composed by three layers, differing in composition:
• An outer superficial layer consisting of lipids,
produced by the meibomian glands;
• An intermediate one, composed of aqueous
components, produced by the lacrimal and
third eyelids superficial glands; and
• An inner layer, consisting of mucin produced
by goblet cells.
The outer superficial oily layer provides
lubrication and prevents overflows of tear from the eye
lid margin. It retards evaporation of the underlying
aqueous layer. This lipid layer acts as a lubricant
allowing for the smooth movement of the eyelids over
the globe. The lipid components also lower the surface
tension of the tear film, which may promotes the
integrity of the aqueous portion. The aqueous layer is
the major component of tear film. It is formed by
electrolytes, water, and proteins. These components are
principally secreted by the lacrimal gland composed of
acini lobules. The lumen of each acinus is lined by
columnar epithelial cells. These cells are surrounded by
a basal layer of myo-epithelial cells enclosed by a
basement membrane. The fluid produced by the
lacrimal gland through intra-lobular and interlobular
ducts drain into the conjunctival space beneath the
upper eyelid. As a result of eyelid movements, the tears
fluid flows over the cornea and produce a thin layer of
the fluid on the cornea. It nourishes and moistens the
cornea further. During the periods between blinks, a
slow and continuous evaporation takes place from the
corneal surface but the thin layer of lipid produced by
tarsal (Meibomian) gland to some extent prevents
evaporation of the aqueous layer. The innermost layer
is produced by the goblet cells of the conjunctival
epithelium and assists in adherence of the pre-corneal
film to the corneal surface (Dartt, 2004). Prabha (2014)
reported that the tears are useful because they have
important proteins, immunoglobulins including its role
in defense of the eye. Tears also have antimicrobial
activity due to lactoferrin present in it. Tears wash
away the unwanted substances present in the eye.
Crying helps in expressing our emotions and also to
overcome sorrow. Tear film helps to maintain visual
acuity and contains major proteins.
4. Different Species
There are adequate researches documenting the
anatomy and histology of lacrimal glands in human and
some other mammals. In all investigated species, the
lacrimal gland has presented more or less a similar
histological structure and is a mixed gland consisting of
tubulo-acinar units (Gargiulo et al., 1999). In most
species, the maximum amount of tears is secreted from
the dorsal lacrimal gland (Carrington et al., 1987;
Nguyen et al., 2006). The examination of lacrimal
glands of human beings, dogs, cats, horses, pigs,
rabbits, sheep, goat and guinea pigs has been described
(Sinha and Calhoun, 1966; Allen et al., 1972;
Krochmalska, 1976; Gillette et al., 1980; Martin et
al.,1988 and Gargiulo et al., 2000). In many species,
the main fraction of tears is produced by lacrimal
glands. In cattle and wild buffalo, no difference is
observed between left and right glands. Moreover, in
these animals no sexual dimorphism is evident in the
case of the lacrimal gland (Pinard et al., 2003).
The lacrimal puncta were absent in the anatomy
of the dromedary lacrimal apparatus. The absence
lacrimal puncta in some mammals does not entirely
deprive the nasal mucosa of the moistening effect of
the lacrimal fluid. But in the camel that moistening
effect is excluded by the absence of the puncta. The
absence of the puncta causes excess lacrimal fluid to
escape by flowing over the lower eyelid. This probably
explains the popular myth that the camel is so
emotional that it sometimes popularly referred as
“sheds tears” (Abdalla et al., 1970 ; Saber and Makady,
1987). The main function of the lacrimal fluid in the
camel is confined to the washing and moistening of the
anterior part of the eyeball. This is an important
function to an animal like the camel which inhabits dry,
hot and sandy land with numerous sand storms.
Probably, the Lacrimation stimulated by the
mechanism of the gustatory-lacrimal reflex between the
gustatory nuclei and the salivary nuclei (including the
lacrimal nuclei) in the brain stem. Lacrimation can also
be a part of the complicated synkineses of yawning,
coughing, and vomiting.
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© 2015 Jakraya Publications (P) Ltd
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Menaka and Puri…Role of Lacrimal Gland in Tear Production in Different Animal Species: A Review
5. Conclusion
The lacrimal glands and its secretary
function in various species is an insight to applied
research models to overcome the different clinical
affections of eyeball at large. In camel, the flow of
the lacrimal secretion does not carried by nasolacrimal duct as in horse. The gender related
differences exists in lacrimal gland of rats, guinea
pig, rabbits and human beings. Some breeds of dog
are more prone to develop kerato-conjunctivitis
sicca with being females are more affected than
males. The lacrimation is physiological event that
to protect the normal pre-corneal surface as well as
it possess bactericidal properties. The modern
therapy as in art of living that encourages the
crying positively and it brings an emotional burst
out and mental well being as in human life.
References
Abdalla O Fahmy MFA and Arnautovic I (1970). Anatomical
study of the lacrimal apparatus of the one-humped
camel. Acta Anatomica, 75: 638-650.
Allen M, Wright P and Reid L (1972). The human lacrimal
gland. A histochemical and organ culture study of the
secretory cells. Archive of Ophthalmology, 88: 493497.
Beech J, Zappala RA, Smith G and Lindborg S (2003).
Schirmer tear test results in normal horses and ponies:
effect of age, season, environment, sex, time of day and
placement of strips. Veterinary Ophthalmology, 6: 251254.
Carrington SD, Bedford PGC, Guillon PP and Woodward EG
(1987). Polarized light biomicroscopic observations on
the precorneal tear film III. The normal tear film of the
cat. Journal of Small Animal Practice, 28: 821-826.
Dartt DA (2004). Control of mucin production by ocular
surface epithelial cells. Experiment Eye Research,
78(2): 173-185.
Gargiulo AM, Coliolo P, Ceccarelli P and Pedini V (1999).
Ultrastructural study of sheep lacrimal glands.
Veterinary Research, 30: 345-351.
Gargiulo AM, Dall’Aglio C, Coliolo P, Cecarelli P and
Pedini V (2000). Complex carbohydrate histochemistry
and ultracytochemistry of the sheep lacrimal gland.
Anatomia Histologia Embryologia, 29: 19-23.
Gillette TE, Allansmith MR, Greiner JV and Jnausz M
(1980). Histologic and immunohistologic comparison
of main and accessory lacrimal tissue. American
Journal of Ophthalmology, 89: 724-730.
Hirayama K, Kagawa Y, Tsuzuki K, Kotani T, Azuma Y,
Yoshino T and Taniyama HA (2000). Pleomorphic
adenoma of the lacrimal gland in a dog. Veterinary
Pathology, 37 (4): 353-356.
Junquira LC and Carneiro J (2003). Basic histology. 10th Ed.
McGraw- Hill Companies. USA 481-482.
Konig HE and Liebich HG (2007). Veterinary anatomy of
domestic mammals, textbook and color atlas. 3rd Ed.
Germany 588-589.
Krochmalska L (1976). Histological and histochemical
picture of the lacrimal gland in guinea pig. Acta
Theriogenology, 21: 31-36.
Martin CL, Munnell J and Kaswan R (1988). Normal
ultrastructure and histochemical characteristics of
canine lacrimal glands. American Journal of
Veterinary Research. 49(9):1566-72.
Mohamadpour AA (2008). Anatomical characterization of
dorsal lacrimal gland in one humped camel (camelus
dromedarius). Journal of Biological Science, 8(6):
1104-1106.
Nguyen DH, Beuermen RW, Meneray M and Toshida H
(2006). Sensory denervation modulatese IF-2 alpha
kinase expression in the rabbit lacrimal gland. Current
Eye Research, 31: 287-295.
Ohashi Y, Dogru M and Tsubota K (2006). Laboratory
findings in tear fluid analysis. Clin Chim Acta, 369: 1728.
Piccione G, Giannetto C, Fazio F and Giudice E (2008).
Daily rhythm of tear production in normal
horse. Veterinary Ophthalmology, 11(Suppl: 1): 57-60.
Pinard CL, Weiss ML, Brightman AH, Fenwick BW and
Davidson HJ (2003). Normal anatomical and
histochemical characteristics of the lacrimal glands in
the American bison cattle. Anatomia Histologia
Embryologia, 32: 257-262.
Prabha JL (2014). Tear Secretion-A Short Review. Journal of
Pharmacology Science and Research, 6(3): 155-157.
Saber AS and Makady FM (1987). Anatomical and clinical
studies on the lacrimal system in camel (Camelus
dromedaries). Assuit Veterinary Medical Journal, 19:
17-21.
Sinha R and Calhoun (1966). A gross, histologic and
histochmeical study of the lacrimal aparatus of sheep
and goat. American Journal of Research, 27: 16331640.
Slatter DH (1973). Keratoconjunctivitis sicca in the dog
produced by oral phenazopyridine hydrochloride.
Journal of Small Animal Practice, 14 (12): 749-771.
Tiffany JM (2008). The normal tear film. Developmental
Ophthalmology, 41: 1-20.
Vinayak A, Greene CE, Moore PA and Powell-Johnson G
(2004). Clinical resolution of Brucella canis-induced
ocular inflammation in a dog. Journal of American
Veterinary Medical Association, 224(11): 1804-1807.
Zhou L, Beuerman RW, Huang L, Barathi A, Foo YH, Li
SFY, Chew FT and Tan D (2007). Proteomic analysis
of rabbit tear fluid: Defending levels after an
experimental corneal wound are correlated to wound
closure. Proteomics, 7: 3194-3206.
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