|Year : 1982 | Volume
| Issue : 6 | Page : 525-530
Experimental amblyopia in kitten histological changes in the lateral geniculate nucleus
BS Goel, SK Mittal
Institute of Ophthalmology. A. M. U. Aligarh, India
B S Goel
Institute of Ophthalmology, A.M.U. Aligarh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Goel B S, Mittal S K. Experimental amblyopia in kitten histological changes in the lateral geniculate nucleus. Indian J Ophthalmol 1982;30:525-30
The site of lesion in the amblyopia has been a controversial issue since the condition was recognised. Several authors has thought the site of lesion to be in the retina, optic nerve, lateral geniculate nucleus or the visual cortex. The most recent theory assumer that it results from the suppression of inputs from the amblyopic eye. The cause of this suppressed inputs to central nervous system may be an atrophy affecting the cells of lateral geniculate nucleus which rely for their vitality on the linkage between the retinal and cortical activity. The present study has, therefore, been undertaken with a view to study the changes in the lateral geniculate nucleus, in experimentally induced amblyopia in kittens.
| Materials and methods|| |
The study has been ,conducted in seven kittens and two adult cats for production of amblyopia by tarsorrhaphy and convergent squint. They were divided into following groups:
Group I (Adult Cat)
A. Normal Cat ... 1
B. Experimented control
(unilateral tarsorrhaphy) ... 1
Group II (Kittens)
A. Tarsorrhaphy ... 4 [Figure l]
B. Convergent Squint ...3 [Figure - 2]
The different procedures adopted were as follows :
I. Clinical examination of the kittens to exclude any ocular disease.
II. Production of Amblyopia.
A. Tarsorrhaphy. was achieved by suturing both the lids together after removing the anterior lid margin throughout its length leaving the medial angle open to allow the drainage from the conjunctival sac.
B. Convergent Squint was produced by removing the lateral rectus muscle of an eye as far as possible.
III. Recording the Visual Acuity.
A. Optokinetic Nystagmus Drum. On which the animals were trained with the sound eye during the period of visual deprivation and the visual acuity of deprived eye was compared with that of the sound eye at different intervals to find out if amblyopia has set in. The test was done at predetermined distances with specific width of stripes on the optokinetic nystagmus drum.
B. Behavioural Tests. were done to assess the development of amblyopia, e.g. Triggered visual placing, i. e. extension of forelimbs to reach a surface towards which the kittens were lowered, and visual startle, i. e. reflex withdrawl of head and eye blinks in response to sudden approach of an object.
These kittens were followed for a varying period of 3 to 9 months. Appearance of Appearance of optokinetic nystagmus in the amblyopic eye at a particular distance as compared to the sound eye and assessment on behavioural tests gave an indication of the development of amblyopia.
IV. Histological Methods.
After the experiment the animals were perfused through heart with 10% formal saline. The brain with lateral geniculate nuclei was removed and fixed in formaline. 5-15 /h thick paraffin sections of the lateral geniculate body were cut in the coronal plane and stained with Hematoxylene and Eosine, Thionine 1% and Toluidine Blue 1%. A quantitative method of measuring the cell and nuclear area and volume was adopted from the method of Schade and Herreveld using an ocular microscope. The cell volume was calculated by the formula 1.04 x nJ6 ab-*/ab (where a & b are major and minor and minor axes respectively). The nuclear volume was calculated by the formula 4/3 n r 3, when the nucleus was spherical and by the formula n/6 ab 2, when the nucleus was ellipsoidal. 50 cells have been measured in each layer on both the sides in each animal and where the number of animals was more than are in the same group, an overall average of these observations have been taken.
| Observation|| |
Normal histological appearance of lateral geniculate nucleus consists of four layers designated as layer 1,2,3 and 4 from dorsal to ventral surface [Figure - 1]. The layers 1 and 3 drive inputs from the opposite eye and layers 2 and 4 from the same side because of crossing of nerve fibres 'at the optic chiasma. Each layer consists of well defined cells with clear outline and cytoplasmic processess, large nucleus and a nucleolus [Figure - 2]. The cells are loosely packed in layers I and 3 whereas they are closely packed in layers 2 and 4. As the cell sizes in different adult cats and kittens vary from animal to animal, therefore, a comparison has been made for cell and nuclear sizes between the deprived and normal layers of the same animal. With this anatomical background the observation have been made in the experimental kittens.
| Tarsorrhaphy group|| |
The tarsorrhaphy in a group of kittens for a varying period of 3-9 months produced a shrinkage in cell and nuclear sizes in layers receiving input from the deprived eye. The maximum shrinkage [Table - 1] and [Table - 2] was seen in the cell area and volume (26. 83% and 24. 83% respectively) in layers 1. However, the shrinkage in layer 3 was marginal (8.24% and 8.41% respectively). Likewise the shrinkage in nuclear area and volume (11.06% and 15.91% resp.) in layear I far exceeded the shrinkage in layer 3 (7.7% and 9.27% resp). The layers 2 and 4 on the same side as deprived eye showed a comparable shrinkage both in cell and nuclear area and volume (i.e. 15.34% & 22.02% in cell area and volume ; and 17.80% & 23.20% in nuclear area and volume respectively in layer 2).
In addition, it was observed that the deprived layers stood out abnormal by virtue of several morphological changes like thining of deprived layers and collapsed appearance throughout its entire extent [Figure - 1]. The most cells in deprived layers were smaller in size with indistinct cell outline, less nuclear material and pale staining of cells [Figure - 3].
The tarsorrhaphy in an adult cat and a kitten at the age of 10--12 weeks did not produce any significant changes between the deprived and non-deprived layers.
It has been observed that a similar shrinkage occurs in cell and nuclear sizes in deprived layers [Table - 3] and [Table - 4], as in the tarsorrhaphy group but the percentage of shrinkage was found to be less. The maximum shrinkage was seen in layer 4 of the same side in the mean cell area and volume (14.98% and 19.83% resp.) and in the mean nuclear area and volume (11.34% and 21.06% resp.). The shrinkage in nuclear area and volume (13.56% and 18.84% resp.) in layer 2 far exceeded the shrinkage in cell area and volume (5.49% and 6 .46% resp.). The shrinkage in cell area and volume (4. 82% & 9.60% resp.) and nuclear area and volume (4.27% & 9.91 resp.) in layer I and in layer 3 (6.08% 9.0%, and 9.79% & 12.25% resp.) was quite less than of other layers.
| Discussion|| |
The observations in general suggest that there is a definite shrinkage in the cell and nuclear and volume among the deprived layers on either side with some diminution in the cell and nuclear diameters and morphological features of cells both in tarsorrhaphy and strabismic group. As the changes in the tarsorrhaphy group was much more pronounced than in the strabismic group, it would mean that complete deprivation of visual stimulation (both form and light) by tarsorrhaphy in the ages of 4-6 weeke kittens and consequent production of amblyopia thereof have definite effect on the lateral geniculate nucleus. However, one would not expect complete deprivation in the squint groug for a comparable time, as there was only deprivation of form stimulation and accordingly the changes are much less.
| Summary|| |
The study deals with six kittens at the age group of 4-6 weeks, one kitten at the age of 10-12 weeks and two adult cats for production of amblyopia by tarsorrhaphy and by production of convergent squint. Definite morphological and histological changes have been seen in the lateral geniculate nucleus as a result of deprivation by tarsorrhaphy and production of convergent squint.
| Acknowledgement|| |
The research has been carried out under the financial aid provided by the Indian Council of Medical Research, on the scheme"Experimental Amblyopia in Kitten-Morphological and Histological changes in central Nervous System and Retina".
[Figure - 1], [Figure - 2], [Figure - 3]
[Table - 1], [Table - 2], [Table - 3], [Table - 4]