|Year : 1985 | Volume
| Issue : 2 | Page : 77-82
Effect of hypothyroidism on intraocular pressure in rabbits
LP Agarwal, VP Gupta, HC Agarwal, RL Mathur
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, A.I.I.M.S. Ansari Nagar, New Delhi, India
L P Agarwal
Institute of Eye Care Training & Research, House No. 10, Sector XV A, Noida-201301 Distt. Ghaziabad
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Agarwal L P, Gupta V P, Agarwal H C, Mathur R L. Effect of hypothyroidism on intraocular pressure in rabbits. Indian J Ophthalmol 1985;33:77-82
|How to cite this URL:|
Agarwal L P, Gupta V P, Agarwal H C, Mathur R L. Effect of hypothyroidism on intraocular pressure in rabbits. Indian J Ophthalmol [serial online] 1985 [cited 2020 Feb 19];33:77-82. Available from: http://www.ijo.in/text.asp?1985/33/2/77/30825
The effect of hypothyroidism on intraocular pressure (TOP) has been studied by various workers in human beings as well in experimental animals,,.. The contention has been supported by reduction of TOP on administration of thyroid extract to control hypothyroid state,. However, some investigators could not established a definite correlation between hypothyroidism and IOP. The present study aims to describe the effect of experimental hypothyroidism on IOP in rabbits.
| Materials and methods|| |
Sixteen albino New Zealand rabbits of either sex weighing about 1 to 1.5 kg. were used. The animals were examined to exclude any systemic or local disorder. The IOP was recorded as described by Heuscher and Flocks for experimental Schiotz tonometry in rabbits. For water drinking test the animals were anaesthetized and an infant feeding tube was passed per orally into the stomach. Tap water 30 ml./kg. body weight was introduced with 10 ml. syringe. Infant feeding tube was taken out and TOP was recorded every 15 minutes for 90 minutes (till the intraocular pressure returned to the initial level). The animals were equally divided into two groups. The group I included control animals and group II included rabbits in which hypothyroidism was produced. Both, groups I and II were divided into two subgroups A & B each having four rabbits. The animals in group II were given subcutaneous injection of 6 mCi of radio-iodine (sodium-iodide-1i31) and group I animals were given 0.1 ml. of normal saline subcutaneously. The animals were observed periodically to notice the signs of hypothyroidism. Total serum tri-iodothyronine (T3) and total serum thyroxine (T4) were estimated by radio-immuno-assay techniques, at the beginning of the experiment and at the end of eight weeks. The clinical diagnosis of hypothyroidism was made on the basis of letharginess, increase in body weight, loss of skin hair, and decrease in heart rate. The clinical diagnosis was confirmed by the total serum-T3 and T4 levels and the histochemical changes of the colloidal iron stained skin biopsy material from each rabbit at the end of eight weeks. After the establishment of hypothyroidism by clinical, serological and histochemical examinations, the animals were further observed for a period of six weeks. Anterior segment assessment, fundus examinations, measurement of TOP and WDT in control and hypothyroid animals were performed at weekly interval for period of six weeks. The animals included in the subgroup A of both the groups the following procedure was performed at the end of the study. After anesthetizing the animals TOP was recorded in both eyes of. control and hypothyroid animals. The left eye of both control and hypothyroid animals received an intracameral inj. of 0.1 ml. of N-saline containing 10 I. U. of purified testicular hyaluronidase using a sharp 27 gauze needle on tuberculin syringe, while the right eye received 0.1 ml. of N-saline in anterior chamber. TOP was again recorded 30 minutes after intracameral injection.
| Observations|| |
The rabbits in control group (group I) did not show significant alterations in body weight skin and heart rate throughout the observation period. The rabbits in group II became progressively lethargic. There was a significant increase in the body weight and decrease in the heart rate with symmetrical loss of large quantity of hair with tense and dry skin at the end of two months after injection of I131. A marked decrease in the total serumT3 from 14.50+22.51 ug% to 53.12+3.93 ug and serum T4 from 6.251.19 ug% to 1.48+ 0.47 ug levels was observed at the end of eight weeks in the rabbits treated with I1'31 which was statistically significant.
Skin of control animals was negative for acid mucopoly-saccharides (AMPS), whereas collodial iron staining of group two animals after the development of hypothyroidism demonstrated bluish staining material (AMPS) in the dermis.
Clinical examination of the anterior segment and ocular fundus showed no changes in all the animals. There was no statistically significant change in the mean TOP in group I rabbits during the whole of the observation period. The IOP of hypothyroid animals increased gradually from the first week of hypothyroidism (i e. eight weeks after injection of 1131) to the end of the study [Table - 1].The rise in TOP was statistically significant from the second week onwards. In majority of the animals the difference in TOP of the two eyes was not significant.
The WDT performed in group I animals showed an TOP rise varying from 1.5 to 6 mm Hg [Table - 2]. The elevation in TOP was less than 4 mm Hg in 10 eyes (62.5%) and 4 to 6 mm Hg in 6 eyes (37.5%). The maximum increase was obtained 30 minutes after water injection. The results of WDT in (group II) test rabbits before the injection of 1131 resembled that of control animals [Table - 2]. WDT in hypothyroid animals at the end of the experiment (i.e. 6 weeks after the establishment of hypothyroidism) revealed a rise in TOP of less than 4mm Hg in two eyes (12.5%), 4 to 6 mm Hg in nine eyes (56.25%), and a rise of more than 6 mm Hg in five eyes (31.25%) [Table - 3]. The maximum rise in IOP was observed between 15 minutes to 30 minutes after water injection. This gradually normalized within one hour in group I rabbits while the exaggerated response persisted even after one hour in hypothyroid rabbits.
There was a statistically significant decrease of IOP in intracameral hyaluronidase treated eyes both in group I and group II rabbits [Table - 4]. A fall of IOP in Group I and group II animals was observed after intracameral saline injection also. However, the decrease of IOP in hyaluronidase treated eyes was significantly more than the saline treated eyes.
| Discussion|| |
An association between open angle glaucoma and hypothyroidism has been reported in human beings as well as in experimental animals by various investigators. Various workers produced hypothyroidism in rabbits and reported rise of IOP following hypothyroidism. Similarly higher IOP values have been reported in patients with hypothyroidism. Furthermore it has been reported that the patients with glaucoma had a tendency to thyroid hypofunction. In the present study there was a gradual elevation of IOP in hypothyroid rabbits. It was not associated with disc changes thus producing a state of ocular hypertension. The findings of this study corroborate above observations.
Our data on the effect of intracameral hyaluronidase and saline injection demonstrated a marked difference in the fall in IOP between hyaluronidase and saline treated eyes in both group I & group 11 animals. The fall in IOP after intracameral saline injection could The explained partly due to pressure on the eye ball while injecting the saline and partly due to leakage of aqueous during withdrawal of needle from anterior chamber.
The fall in IOP after intracameral hyaluronidase was more in hypothyroid animals as compared to control animals. The effect of intracameral hyaluronidase on IOP and facility of outflow has been studied by various workers & decrease in the resistance of aqueous outflow in animal eyes including rabbits has been demonstrated.
The results of WDT in control and hypothyroid animals revealed that in majority of control animals (10 eyes) IOP rise was less than 4 mm Hg and none revealed a rise of more than 6 mm Hg. Whereas in hypothyroid animals, IOP rise of 4-6 mm Hg was noted in 9 eyes & more than 6 mm Hg in five eyes. Moreover the hypothyroid animals showed exaggerated response to water injection which persisted for longer duration than control animals as well as in the same animal prior to the development of hypothyroidism. Similar results have been described by Koop3 in hypothyroid rabbits.
The exact mechanism by which hypothyroidism causes elevation of IOP is not known. The presence of hyaluronidase sensitive AMPS in the region of trabecular meshwork have been demonstrated in human beings as well as in experimental animals, It has been speculated that in hypothyroidism the pathological deposition of AMPS in the region of trabecular meshwork might be responsible for the impairment of outflow facility resulting in elevation of IOP.
In this study the histochemical examination of the angle region revealed increased accumulation of AMPS in the trabecular meshwork and along the walls of canal of Schlemm in hypothyroid rabbits resulting in decreased facility of outflow. This could be the cause of elevated IOP and exaggerated response in WDT in hypothyroid rabbits. In hyaluronidase treated eyes partial or complete disappearance of AMPS in the trabecular meshwork could explain marked decrease in IOP following intracameral injection of hyaluronidase.
| Summary|| |
Sixteen normal albino rabbits were equally divided into control and test groups. Hypothyroidism was produced in test animals by subcutaneous injection of radio-iodine. Various parameters studied were signs of hypothyroidism, total serum tri-iodothyronine (T3) and thyroxine (T4), intraocular pressure (TOP), water drinking test (WDT) and the effect of intracameral hyaluronidase on TOP. Statistically significant elevation of IOP, exaggerated response in WDT and fall in IOP after intracameral hyaluronidase were observed in hypothyroid animals. This elevated TOP and exaggerated response in WDT in hypothyroid rabbits was due to increased accumulation of acid mucopolysaccharides in the trabecular meshwork and canal of Schlemm.
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[Figure - 1]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]