EVALUATION OF TEAR SECRETION IN GOAT KIDS WITH COCCIDIOSIS BY SCHIRMER TEAR TEST

Document Type : Research article

Authors

1 Department of Surgery, Faculty of Veterinary Medicine, Siirt University, 56100, Siirt, Turkey

2 Department of Internal Medicine, Faculty of Veterinary Medicine, Siirt University, Siirt, Turkey.

Abstract

Coccidiosis, caused by Eimeria species is common in 2–4 month old goats, are highly pathogenic in goat kids. The most common clinical findings are dehydration, weakness, weight loss, diarrhea and anemia. The aim of this study is to determinate of tear secretion in goats kids with coccidiosis and healthy ones by utilizing  STT. A total of 20 pure hair goats kids aged between 2-4 months, among which 10 were with clinical coccidiosis (Group 1, n=10) and 10 were in the healthy conditions (Group 2, n=10), in a single farm located at Siirt, Turkey. Fecal samples were examined microscopically for concentrated flotation and the presence of oocysts. STT test was performed on both eyes of healthy and clinical coccidiosis and results were recorded. Group 1 Mean ± SD STT values for right and left eye were 5.8 ± 1.75 and 5.1 ± 1.66 mm/min and Group 2 Mean ± SD STT values for right and left eye were 13.4 ± 2.37 and 12.5 ± 2.12 mm/min, respectively. Comparison of STT values of the right eyes with left eyes did not differ significantly in both groups (P = 0.271, P = 0.235). Both eye’s STT results combined to compare groups. The mean of Group 1 (5.45 ± 1.7 mm/min) was found to be significantly lower than the mean of Group 2  (12.95 ± 2.24 mm/min)  as a result (P < 0.001). As a result of this study, the amount of tear secretion was determined with the STT and there was statistically significant difference between healthy and goat kids clinical coccidiosis.

Keywords

Main Subjects


Assiut University web-site: www.aun.edu.eg

 

EVALUATION OF TEAR SECRETION IN GOAT KIDS WITH COCCIDIOSIS  BY SCHIRMER TEAR TEST

 

Mustafa Barış AKGÜL1 AND Gülşah AKGÜL 2

1 Department of Surgery, Faculty of Veterinary Medicine, Siirt University, 56100, Siirt, Turkey

2 Department of Internal Medicine, Faculty of Veterinary Medicine, Siirt University, 56100,

Siirt, Turkey

 

Received: 13 December 2020;     Accepted: 27 December 2020

 

 

ABSTRACT

 

Coccidiosis, caused by Eimeria species is common in 2–4 month old goats, are highly pathogenic in goat kids. The most common clinical findings are dehydration, weakness, weight loss, diarrhea and anemia. The aim of this study is to determinate of tear secretion in goats kids with coccidiosis and healthy ones by utilizing  STT. A total of 20 pure hair goats kids aged between 2-4 months, among which 10 were with clinical coccidiosis (Group 1, n=10) and 10 were in the healthy conditions (Group 2, n=10), in a single farm located at Siirt, Turkey. Fecal samples were examined microscopically for concentrated flotation and the presence of oocysts. STT test was performed on both eyes of healthy and clinical coccidiosis and results were recorded. Group 1 Mean ± SD STT values for right and left eye were 5.8 ± 1.75 and 5.1 ± 1.66 mm/min and Group 2 Mean ± SD STT values for right and left eye were 13.4 ± 2.37 and 12.5 ± 2.12 mm/min, respectively. Comparison of STT values of the right eyes with left eyes did not differ significantly in both groups (P = 0.271, P = 0.235). Both eye’s STT results combined to compare groups. The mean of Group 1 (5.45 ± 1.7 mm/min) was found to be significantly lower than the mean of Group 2  (12.95 ± 2.24 mm/min)  as a result (P < 0.001). As a result of this study, the amount of tear secretion was determined with the STT and there was statistically significant difference between healthy and goat kids clinical coccidiosis.

 

Keywords: Coccidiosis, Goat Kids, Schirmer Tear Test, Tear.

 

 


INTRODUCTION

 

Coccidiosis, caused by Eimeria species is common in 2–4 month old goats, are highly pathogenic in goat kids (Foreyt, 1990; Valentine et al. 2007; Chartier and Paraud, 2012). Coccidiosis in goats is an important disease   caused  by  complex    interactions

 

 


Corresponding author: Gülşah AKGÜL

E-mail address: gulsahvet@hotmail.com

Present address: Department of Internal Medicine, Faculty of Veterinary Medicine, Siirt University, 56100, Siirt, Turkey

between parasites and host, and many factors affect the severity of the disease (Temizel et al., 2011). Clinical coccidiosis occurs when many sporulated oocysts are swallowed as a result of reduced resistance of animal (Chartier and Paraud, 2012). It invades and destroys intestinal cells, causing blood and electrolyte loss and poor absorption of nutrients (Radostits and Gay, 2006). The most common clinical findings are dehydration, weakness, weight loss, diarrhea and anemia (Soliman and Zalat, 2003). Diarrhea causes dehydration which defined as a decrease in extra and / or intracellular fluid volume; mainly caused by reduced fluid intake and / or excessive fluid loss. Excessive fluid loss; high fever, especially diarrhea and vomiting shock, excessive exercise, polyuria, and burns. It is manifested by decreased appetite, dry skin, dry eye and mouth, darkening of urine color (Gayton, 2009).

 

The eye has developed specific adaptations in different animal species, it is a very complex and sensitive organ where many different departments work together in harmony to provide vision (Mancinelli, 2011). The tear system or lacrimal system is the entire canal system where tears are secreted and distributed (Yıldız, 2011). Ocular tears are formed by the secretion of many glands (Gum, 1991; Aguirre et al., 1995; İzci et al., 1995). The outer lipid layer is produced by Meibomian and Zeis glands located in the upper and lower eyelids. The middle layer is produced by the orbital tear gland and the third eyelid gland. The innermost mucoprotein layer is generated by the conjunctival goblet and corneal epithelial cells (Gellat et al., 1975; Slatter, 1990; Whitley et al., 1991). Tears are necessary to maintain normal function of the conjunctiva and cornea. Tears play an important role in removing foreign substances from the eye, provide the necessary nutrient content for the avascular cornea, and contain immunoglobulin and lysosomes, which are significant for the defense mechanism of the eye (Gum, 1991).

 

STT is utilized to determine the amount of tear secretion in different strains, the break-up time (BUT) test is used for stability of precorneal tear film, and dyeing tests such as rose Bengal, lissamine green, and fluorescein are used to control the integrity of the precorneal tear film (Vashisht and Singh, 2011). The STT was introduced over a century ago and is still widely used in clinical practice (Saleh et al., 2006).

The aim of this study is to comparatively evaluations of tear secretion in healthy and coccidiosis in goats kids, raised in the Siirt region by utilizing STT.

 

MATERIALS AND METHODS

 

Animals and sample collection:

The study conducted with 20 pure hair goats kids aged between 2-4 months, among which 10 were with clinical coccidiosis (Group 1, n=10) and 10 were in the healthy conditions (Group 2, n=10), in a single farm located at Siirt, Turkey. Housing, feeding, and management conditions were same for all kids. The clinical examinations (body temperature, pulsation, number of respirations, lymph nodes, tracheal palpation, lung auscultation and percussion) of all animals in the study were extensively performed (Batmaz, 2020). Animals with weakness, loss of weight, diarrhoea hyperemia, were evaluated as having coccidiosis and were allocated in Group 1. The animals that did not lose appetite and performance, and had normal clinical examination results and were allocated in Group 2.

 

Parasitological examination:

Fecal samples were taken separately from the rectum of the animals. In this study, 20 fecal samples were examined. Fecal samples were kept in the feces cup, labeled and stored at 4 °C until examination. Samples were examined microscopically for concentrated flotation and the presence of oocysts (Temizel et al., 2011).

 

Implementing of test:

The animals were placed in a closed and low-light area for the application of the STT (Schirmer Tear Test, ERC, Turkey). The test strip was placed towards the test subject’s lower fornix through the middle third of the eye and the outer third of the eye by folding it about 5 mm from its upper end. At the end of 1 min of waiting time, the test was performed and the numerical value was recorded. ests were carried out by the same researcher, first on the right-hand side and then on the left-hand side of the test subject, at control visits while animals were on their feet.

 

Statistical analysis:

Data were tested for normality and homogeneity of variances with Shapiro-Wilk and Levene tests. Mean and SD were calculated for all eyes combined and for right and left eyes separately and indicated as Mean ± SD values. The data was normally distributed and hence Paired Sample t-test was used to assess the difference between right and left eye tear productions in each group individually. Student's t-test was used to determine  differences in measurements from both eyes between groups. Significant differences among groups means were determined at P < 0.05. The Statistical Package for the Social Sciences (SPSS, version 14.01, IBM software) was used for performing statistical calculations.

 

RESULTS

 

Group 1 Mean ± SD STT values for right and left eye were 5.8 ± 1.75 and 5.1 ± 1.66 mm/min and Group 2 Mean ± SD STT values for right and left eye were 13.4 ± 2.37 and 12.5 ± 2.12 mm/min, respectively. Comparison between STT values of right eyes and left eyes  revealed no significant differences in neither of groups (P = 0.271, P = 0.235). Both eye’s STT results combined to compare groups.  The mean of Group 1 (5.45 ± 1.7) was found to be significantly lower than the mean of Group 2  (12.95 ± 2.24)  as a result (P < 0.001) (Table 1, Figure 1).

 

 

Table 1:  Mean ± SD results as collected from right, left and both eyes.

 

Group

N

Mean

SD

P value

Group 1

Right eye

10

5.8

1.75

0.271

Left eye

10

5.1

1.66

0.271

Group 2

 

Group 1

Group 2

Right eye

10

13.4

2.37

0.235

Left eye

Both eye

Both eye

10

20

20

12.5

5.45

12.95

2.12

1.70

2.24

0.235

<0.001

<0.001

STT (mm/min)

 

 

Figure 1: Results as collected from right, left and both eyes


DISCUSSION

 

Coccidia is a protozoan parasites that infect goats, lambs, cattle and many animals. Animals can be exposed to a large number of parasites and develop diarrhea. Diarrhea is not usually bloody in goat kids, but it contains blood and mucus and can be very watery. The most common signs are dehydration, anorexia, weakness and diarrhea (Pugh, 2002).

 

Dehydration can have a number of unwanted effects on body, and eyes are no exception. Eyes need water just as much as joints or kidneys in order to function properly. Dehydration occurs when there is too much fluid loss, especially diarrhea (Batmaz, 2020). Dehydration have some symptoms such as dry mouth, decreased urine output, muscle cramps, lighth eadedness and a lack of tear production. (McCarty et al., 1998).

 

Ophthalmological examinations are important in food-producing animals because they are economically valuable (Ribeiro et al., 2010). Ophthalmic parameters are still rarely studied in goats and need to be improved. The STT, is widely used in both human and veterinary ophthalmology as a basic assessment of tear production, designed by Otto Schirmer (Williams, 2005).

 

STT should be performed early in the examination, before applying any liquid to the eye or manipulating the eye, before any other procedures and tests (Rosolen et al., 2009). In the presented study, tear test was applied as stated by the researcher.

 

STT 1 measures not only basal tear production, but also reflex tear production caused by stimulation of trigeminal nerve endings due to local irritations (Koç et al., 2005, Rosolen et al., 2009, Şındak et al., 2010). STT 2 is a more rare method and is used only to measure basal tear production by applying topical anesthesia to the eye and eliminating reflex tear production (Koç et al.,  2005, Rosolen et al., 2009, Trbolova and Ghaffari, 2011). Normal STT-2 levels are half or a little more than STT-1 levels (Rosolen et al., 2009). In a study on dogs, STT-1 values were higher than STT-2 values. Beech et al. 2003, Alkan et al. 2004). In a study on pigs, it was again stated that STT-2 values were significantly lower than STT-1 values (Trbolova and Ghaffari, 2011). STT-1, which is applied without the use of topical anesthesia, is frequently used in clinical studies to evaluate basal and reflex lacrimation (Koç et al., 2005). As a result of the examination of all these studies in the presented study, STT-1 level was measured by measuring. STT – 1 was applied separately for the right and left eyes for comparison.

 

Broadwater et al. (2007) showed that in adult pygmy goats, tear secretion amount of mean STT values were 15.8 mm/min, with a range of 10–30 mm/min. Koç et al. (2005) showed, the mean STT valuee were 17.1 ± 2.8 mm / min in dogs, 16.2 ± 3.8 mm / min in cats. Trbolova and Ghaffaari (2011) showed, tear secretion amount of mean STT values were 15.8 ± 5.7 mm / min in goats, 18,5 ± 2.5 mm / min in sheep. And  Beech et al. (2003) showed that in horses, the mean STT values were 12.72 ± 9.07 mm / min. In presented study, was noted mean STT values were 12.95  ± 2.24 mm/min in healthy goats kids.

 

In a study on Saanen goats, it was revealed that the mean STT values for the 45- and 180-day-old animals were not statistically different between the right eye and the left eye, while the mean STT values in the 549-day-old animals were statistically lower than the left eye (Ribeiro et al., 2010).       

 

Although it has been found that there is a similar relationship between age and tear production in animals and people, some studies have discussed that there is no relationship between tear production and age, sex, or weight (Mathers et al., 1996; Moss et al., 2004). But some researchers have argued the opposite (Saito and Kotani 2001; Ghaffari et al., 2010). In this study, goats kids aged between 2-4 months and weight average 4 kg used.

 

Tears are very important for health of the conjunctiva and cornea. The decrease in production of liquids from the tear glands affects the strength of the tear membrane (Trbolova and Ghaffari, 2012). Lack of tears can cause serious problems in the long run. If left untreated, it may progress to vision loss in the future. Tear value was found to be low in animals with coccidiosis (mean of Group 1 (5.45 ± 1.7). Therefore, this presented study is important because it is the first one, and deeper studies should be conducted examining the conjunctiva and cornea.

 

In some studies it has been said that the method of application has complications. (Sakamoto et al., 1993, Hakanson et al., 1997, Martins et al., 2009) of STT, reported that they did not any complications during and after the procedure. In our study, we did not record any complications as we accurately placed sterile STT strips.

 

CONCLUSION

 

As a result of this study, the amount of tear secretion was determined  with the STT and there was statistically significant difference between healthy and goat kids with clinical coccidiosis. Our results showed that tear secretion values is significantly lower in goat kids with coccidiosis, when compared to healthy. We believe that tear secretion decreases due to fluid loss in the body caused by clinical symptoms of coccidiosis. This study was done for the first time and more studies must to be performed in order to clarify the impact of tear secretion values in goat kids with coccidiosis.

 

REFERENCES

 

Aguirre, G.A.; Rubin, L.F. and Harvey, C.E. (1995): Keratoconjunctivitis sicca in dogs. Journal of the American Veterinary Medical Association, 206: 1286-1289.

Alkan, F.; İzci, C.; Tepeli, C. and Koç, Y. (2004): Evaluation of the Schirmer tear test in two Turkish breeds of shepherd dogs. Revue Méd. Vét, 155: 67-70.

Batmaz, H. (2020): Koyun Ve Keçilerin İç Hastalıkları, Semptomdan Tanıta Tanıdan Sağaltıma (2nd Edn.). Nobel Tıp kitapevi Ltd. Şti, ankara. pp. 118.

Beech, J.; Zappala, R.A.; 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: 251–254.

Broadwater, J.J.; Schorling, J.J. and Herring, I.P. (2007): Ophthalmic examination findings in adult pygmy goats (Capra hicus). Veterinary Ophthalmology, 10 (5): 269-273.

Chartier, C. and Paraud, C. (2012): Coccidiosis due to Eimeria in sheep and goats, a review. Small Ruminant Research, 103: 84-92.

Foreyt, W. (1990): Coccidiosis and cryptosporidiosis in sheep and goats. Veterinary Clinics of North America: Food Animal Practice, 6: 655-670.

Ghaffari, M.S.; Malmasi, A. and Bokaie, S. (2010): Effect of acepromazine or xylazine on tear production as measured by schirmer tear test in normal cats. Veterinary Ophthalmology, 13: 1-3.

Gayton, J.L. (2009): Etiology, prevalence, and treatment of dry eye disease. Clinical Ophthalmology (Auckland, NZ), 3: 405.

Gelatt, K.N.; Peiffer, R.L. and Erickson, J.L. (1975): Evaluation of tear formation in the dog, using a modification Schirmer tear test. Journal of the American Veterinary Medical Association, 166: 368-370.

Gum, G.G. (1991): Physiology of the eye (2nd Edn.). Lea and Febiger, Philadelphia. pp. 125-126.

Hakanson, N.W. and Arnesson, K. (1997): Temporal variation in tear production in normal beagle dogs as determined by schirmer tear test. Veterinary and comparative ophthalmology, 7: 196-203.

İzci, C.; Avki, S. and Alkan, F. (1995): An experimental study on the effect of topically used atropine on tear production of dogs. Veteriner Bilimleri Dergisi, 11: 25-31.

Koç, Y.; Alkan, F. and Tepeli, C. (2005): Schirmer tear test in different rabbit breeds. Hayvancılık Araştırma Dergisi, 15: 2: 1-5.

Mancinelli, E. (2011): The rabbit eye: anatomy and common diseases. Erişim:http://www.gwexotics.com/wccms-resources/7/9/b/8/a4c21414-a660-11e0-a685- 0050568626ea.

Martins, B.C.; Ribeiro, A.P. and Laus, J.L. (2009): Glaucoma. Oftalmologia Clínica e Cirúrgica em Cães e em Gatos. roca, sãopaulo. pp. 151-167.

Mathers, W.D.; Lane, J.A. and Zimmerman, M.B. (1996): Tear film changes associated with normal aging. Cornea, 15: 229-234.

McCarty, C.A.; Bansal, A.K. and Livingston, P.M. (1998): The epidemiology of dry eye in Melbourne, Australia. Ophthalmolog, 105: 1114-1119. 

Moss, S.E.; Klein, R. and Klein, B.E.K. (2004): Incidence of dry eye in an older population. Archives of Ophthalmology, 122: 369-373.

Pugh, DG. (2002): Sheep and Goat Medicine. Normal Values and Conversions. Elsevier, Philadelphia. pp. 85.

Radostits, O.M. and Gay, C.C. (2006): Hinchcliff, Constable PD Veterinary Medicine: A textbook of the diseases of cattle, horses, sheep, pigs and goats (10th Edn.). W.B Saunders, Edinburgh. pp. 1498-1506.

Ribeiro, A.P.; Piso, D.Y.T.; Padua, I.R.M.; Silva, M.L. and Laus, J.L. (2010): Intraocular pressure and tear secretion in Saanen goats with different ages. Pesquisa Veterinária Brasileira, 30 (9): 798-802.

Rosolen, S.G.; Multari, D.; Woods, M. and Jongh, O. (2009): Diagnostics. Small Animal Ophthalmology.(4thEd) China. RDC Group Limited;Chapter 2.pp.15.

Saito, A. and Kotani, T. (2001): Estimation of lacrimal level and testing methods on normal beagles. Veterinary Ophthalmology, 4: 7-13.

Sakamoto, R.; Bennett, E.S. and Henry, V.A. (1993): The phenol red thread tear test: a crosscultural study. Investigative Ophthalmology and Visual Science, 34: 3510-3514.

Saleh, T.A.; McDermott, B. and Bates, A.K. (2006): Phenol red thread test vs Schirmer’s test: a comparative study. Eye, 20: 913-915.

Slatter, D.H. (1990): Lacrimal system. Fundamentals of Veterinary Ophthalmology (2nd Edn.). Saunders Company, Philadelphia. pp. 237-256.

Soliman, M.F.M. and Zalat, S.M. (2003): Prevalence and intensity of Nematodirus sp. and Eimeriasp. infections in the domestic goats of St. Katherine’s Protectorate (Sinai, Egypt): relations with some ecological and biological factors. Egyptian Journal of Botany, 5: 78-85.

Şındak, N.; Kandemir, L.; Yertürk, M. and Biricik, H.S. (2010): Measurement of phenol red thread tear test in Arabian andthroughbred horses. Veterinary Ophthalmology, 13: 219–221.

Temizel, E.M.; Demir, G.; Selcuk, O. and Çatık, S. (2011): Effect of treatment with cylindamycine in an outbreak of coccidiosis in goat kids in Turkey. Journal of Biological and Environmental Sciences, 5 (13): 37-40.

Trbolova, A. and Ghaffari, M.S. (2011): Reference values for Schirmer tear tests I and II in clinically normalpigs. Veterinary Ophthalmology, 1–3.

Trbolova, A. and Ghaffari, M.S. (2012): Reference values for Schirmer tear tests I and II in clinically normal pigs. Veterinary Ophthalmology, 15: 180-182.

Valentine, B.A.; Cebra, C.K. and Taylor, G.H. (2007): Fatal gastrointestinal parasitism in goats: 31 cases (2001–2006). Journal of the American Veterinary Medical Association, 231: 1098-1103.

Vashisht, S. and Singh, S. (2011): Evaluation of phenol red thread test versus Schirmer test in dry eyes: a comparative study. International Journal of Applied and Basic Medical Research, 1: 40-42.

Whitley, R.D.; McLaughlin, S.A. and Gilger, B.C. (1991): The treatments for keratoconjunctivitis sicca. Veterinary Medicine Small Animal Clinician, 10: 1077-1093.

Williams, D.L. (2005): Analysis of tear uptake by the Schirmer tear test strip in the canine eye. Veterinary Ophthalmology, 8: 325-330.

Yıldız, Y.Z. (2011): Göz anatomisi; 2010. Erişim:http://www.ctf.edu.tr/anabilimdallari/pdf/416/3001x-G%C3%B6z%20

Anatomisi Ders%20PPT-13.10.%

202010.pdf.

 

 

REFERENCES
 
Aguirre, G.A.; Rubin, L.F. and Harvey, C.E. (1995): Keratoconjunctivitis sicca in dogs. Journal of the American Veterinary Medical Association, 206: 1286-1289.
Alkan, F.; İzci, C.; Tepeli, C. and Koç, Y. (2004): Evaluation of the Schirmer tear test in two Turkish breeds of shepherd dogs. Revue Méd. Vét, 155: 67-70.
Batmaz, H. (2020): Koyun Ve Keçilerin İç Hastalıkları, Semptomdan Tanıta Tanıdan Sağaltıma (2nd Edn.). Nobel Tıp kitapevi Ltd. Şti, ankara. pp. 118.
Beech, J.; Zappala, R.A.; 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: 251–254.
Broadwater, J.J.; Schorling, J.J. and Herring, I.P. (2007): Ophthalmic examination findings in adult pygmy goats (Capra hicus). Veterinary Ophthalmology, 10 (5): 269-273.
Chartier, C. and Paraud, C. (2012): Coccidiosis due to Eimeria in sheep and goats, a review. Small Ruminant Research, 103: 84-92.
Foreyt, W. (1990): Coccidiosis and cryptosporidiosis in sheep and goats. Veterinary Clinics of North America: Food Animal Practice, 6: 655-670.
Ghaffari, M.S.; Malmasi, A. and Bokaie, S. (2010): Effect of acepromazine or xylazine on tear production as measured by schirmer tear test in normal cats. Veterinary Ophthalmology, 13: 1-3.
Gayton, J.L. (2009): Etiology, prevalence, and treatment of dry eye disease. Clinical Ophthalmology (Auckland, NZ), 3: 405.
Gelatt, K.N.; Peiffer, R.L. and Erickson, J.L. (1975): Evaluation of tear formation in the dog, using a modification Schirmer tear test. Journal of the American Veterinary Medical Association, 166: 368-370.
Gum, G.G. (1991): Physiology of the eye (2nd Edn.). Lea and Febiger, Philadelphia. pp. 125-126.
Hakanson, N.W. and Arnesson, K. (1997): Temporal variation in tear production in normal beagle dogs as determined by schirmer tear test. Veterinary and comparative ophthalmology, 7: 196-203.
İzci, C.; Avki, S. and Alkan, F. (1995): An experimental study on the effect of topically used atropine on tear production of dogs. Veteriner Bilimleri Dergisi, 11: 25-31.
Koç, Y.; Alkan, F. and Tepeli, C. (2005): Schirmer tear test in different rabbit breeds. Hayvancılık Araştırma Dergisi, 15: 2: 1-5.
Mancinelli, E. (2011): The rabbit eye: anatomy and common diseases. Erişim:http://www.gwexotics.com/wccms-resources/7/9/b/8/a4c21414-a660-11e0-a685- 0050568626ea.
Martins, B.C.; Ribeiro, A.P. and Laus, J.L. (2009): Glaucoma. Oftalmologia Clínica e Cirúrgica em Cães e em Gatos. roca, sãopaulo. pp. 151-167.
Mathers, W.D.; Lane, J.A. and Zimmerman, M.B. (1996): Tear film changes associated with normal aging. Cornea, 15: 229-234.
McCarty, C.A.; Bansal, A.K. and Livingston, P.M. (1998): The epidemiology of dry eye in Melbourne, Australia. Ophthalmolog, 105: 1114-1119. 
Moss, S.E.; Klein, R. and Klein, B.E.K. (2004): Incidence of dry eye in an older population. Archives of Ophthalmology, 122: 369-373.
Pugh, DG. (2002): Sheep and Goat Medicine. Normal Values and Conversions. Elsevier, Philadelphia. pp. 85.
Radostits, O.M. and Gay, C.C. (2006): Hinchcliff, Constable PD Veterinary Medicine: A textbook of the diseases of cattle, horses, sheep, pigs and goats (10th Edn.). W.B Saunders, Edinburgh. pp. 1498-1506.
Ribeiro, A.P.; Piso, D.Y.T.; Padua, I.R.M.; Silva, M.L. and Laus, J.L. (2010): Intraocular pressure and tear secretion in Saanen goats with different ages. Pesquisa Veterinária Brasileira, 30 (9): 798-802.
Rosolen, S.G.; Multari, D.; Woods, M. and Jongh, O. (2009): Diagnostics. Small Animal Ophthalmology.(4thEd) China. RDC Group Limited;Chapter 2.pp.15.
Saito, A. and Kotani, T. (2001): Estimation of lacrimal level and testing methods on normal beagles. Veterinary Ophthalmology, 4: 7-13.
Sakamoto, R.; Bennett, E.S. and Henry, V.A. (1993): The phenol red thread tear test: a crosscultural study. Investigative Ophthalmology and Visual Science, 34: 3510-3514.
Saleh, T.A.; McDermott, B. and Bates, A.K. (2006): Phenol red thread test vs Schirmer’s test: a comparative study. Eye, 20: 913-915.
Slatter, D.H. (1990): Lacrimal system. Fundamentals of Veterinary Ophthalmology (2nd Edn.). Saunders Company, Philadelphia. pp. 237-256.
Soliman, M.F.M. and Zalat, S.M. (2003): Prevalence and intensity of Nematodirus sp. and Eimeriasp. infections in the domestic goats of St. Katherine’s Protectorate (Sinai, Egypt): relations with some ecological and biological factors. Egyptian Journal of Botany, 5: 78-85.
Şındak, N.; Kandemir, L.; Yertürk, M. and Biricik, H.S. (2010): Measurement of phenol red thread tear test in Arabian andthroughbred horses. Veterinary Ophthalmology, 13: 219–221.
Temizel, E.M.; Demir, G.; Selcuk, O. and Çatık, S. (2011): Effect of treatment with cylindamycine in an outbreak of coccidiosis in goat kids in Turkey. Journal of Biological and Environmental Sciences, 5 (13): 37-40.
Trbolova, A. and Ghaffari, M.S. (2011): Reference values for Schirmer tear tests I and II in clinically normalpigs. Veterinary Ophthalmology, 1–3.
Trbolova, A. and Ghaffari, M.S. (2012): Reference values for Schirmer tear tests I and II in clinically normal pigs. Veterinary Ophthalmology, 15: 180-182.
Valentine, B.A.; Cebra, C.K. and Taylor, G.H. (2007): Fatal gastrointestinal parasitism in goats: 31 cases (2001–2006). Journal of the American Veterinary Medical Association, 231: 1098-1103.
Vashisht, S. and Singh, S. (2011): Evaluation of phenol red thread test versus Schirmer test in dry eyes: a comparative study. International Journal of Applied and Basic Medical Research, 1: 40-42.
Whitley, R.D.; McLaughlin, S.A. and Gilger, B.C. (1991): The treatments for keratoconjunctivitis sicca. Veterinary Medicine Small Animal Clinician, 10: 1077-1093.
Williams, D.L. (2005): Analysis of tear uptake by the Schirmer tear test strip in the canine eye. Veterinary Ophthalmology, 8: 325-330.
Yıldız, Y.Z. (2011): Göz anatomisi; 2010. Erişim:http://www.ctf.edu.tr/anabilimdallari/pdf/416/3001x-G%C3%B6z%20
Anatomisi Ders%20PPT-13.10.%
202010.pdf.