Year : 1971 | Volume
: 19 | Issue : 2 | Page : 43--48
Amblyopia development due to lack of functional, stimulation of visual pathways
Centre de Neurochimie 11, Rue Humann, Strasbourg, France
Dr. Rajendra Prasad, Centre for Ophthalmic Sciences, All-India Institute of Medical Sciences, New Delhi, India
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Goswamy S. Amblyopia development due to lack of functional, stimulation of visual pathways.Indian J Ophthalmol 1971;19:43-48
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Goswamy S. Amblyopia development due to lack of functional, stimulation of visual pathways. Indian J Ophthalmol [serial online] 1971 [cited 2021 Jun 17 ];19:43-48
Available from: https://www.ijo.in/text.asp?1971/19/2/43/34994
Vision, which contributes a great deal towards development of intelligence and enhancement of knowledge, is a sum of specific responsiveness and activity in living neurons of visual system, functioning under adequate physiological conditions. Therefore, if there are ophtalmoscopically unobservable changes in structure and composition of the visual pathways, or when there is lack of adequate physiological conditions, the result is likely to be poor vision, that is, amblyopia. Whereas a good deal of attention has been paid to the structural changes of visual pathways, much needs to be learnt about its specific responsiveness to the most appropriate stimulus, the light. In this context, we have started to explore the dynamic factors involved in vision process by studying the role of light in the biosynthesis of ribonucleic acid and the electrophysiological functions of developing visual pathways.
Methods and Material
The experiments were performed on rabbits (fauve de Bourgogne strain) during different stages of development from birth onwards. (1) The electrophysiological study included the investigation of visual evoked potentials from the visual cortex, lateral geniculate body and the superior colliculi according to the technique detailed previously (Bonaventure. Goswamy and Karli  ). (2) The biochemical investigations consisted of estimation of free nucleotides by orcinol reaction (Mejbaum) from acidsoluble fraction of perchloric acid (PCA) extracts of retina and visual cortex. The specific activity of P-RNA was determined in the acidinsoluble fraction of the PCA extracts of retina and visual cortex, which had been previously incubated with radio-active phosphorus. The nucleic acids were determined according to techniques described earlier (Mendal and Goswamy  ). (3) The radioactivity was measured by scintillation method in Packard spectrometer. (4) To evaluate as to which layer of retina shows maximum changes in RNA synthesis during the course of maturation, histoautoradiography was performed according to the technique reported earlier ( Goswamy and Mandel).
The above biochemical and electrophysiological parameters studied during the course of normal development of visual pathways were compared with those obtained from the animals born and brought up in total darkness, that is, devoid of all functional (visual) stimuli since birth onwards.
Observations and Discussion
As evident from our previous publications, the maturation of normal visual pathways in rabbits can be divided into three phases, both electrophysiologically (Bonaventure, Goswamy and Karli  ) and biochemically, (Goswamy and Mandel  ) The first phase is from birth to the fiirst opening of the eyes in rabbits (about 8 to 10 days). In this phase, there is an increase of nucleic acids reflecting morphological development of visual pathways, but neither electroretinogram (ERG) nor visual evoked responses from the visual cortex could be registered following photicstimulation. The second phase is at and about the time of first opening of the eyes, when there is reduction in the nucleic acids level and the first appearance of the electrical responses, both in the retina and visual cortex.
After this period, the third phase is characterized by a progressive increase of ribonucleic acids and proteins per cell, and the electrical responses from the retina and visual cortex show an evolution in the form, amplitude and latency. By about three weeks of age, both the biochemical and electrophysiological parameters of the visual pathways in rabbits attain definitive characteristics of the adult, that is, from this age onwards, the visual pathways of rabbits have achieved full functional maturity.
Our subsequent investigations further revealed that there is a progressive increase of the total free nucleotides in retina and visual cortex from birth to 21 days of age [Table 1]. There is also a progressive increase in the conversion of nucleotide triphosphates into RNA which is reflected by the specific activity of P-RNA as related to P-alpha in the free nucleotides [Table 2]
The histoautoradiographic study of the normal retina supports the three phases of retinal maturation [Figure 1]. The first, before opening of the eyes, having a high rate of RNA turnover; second, at about the time of opening of the eyes, with lower RNA turnover; and a third, after the opening of the eyes and related with the functional response to visual stimuli, accompanied by a progressive increase of RNA synthesis upto about 21 days. Furthermore the RNA synthesis is more in the right eye (stimulated with st r ong flashes of light prior to enucleation) as compared to the left, at each stage of development. This investigation suggests that the changes in RNA synthesis following photic stimulation are situated mainly in the outer nuclear layer of the retina, which are the nuclei of the rods and cones.
In the rabbits born and brought up in total darkness, the initial surface-positive component of the visual evoked potentials at the level of visual cortex (area 17) appears only from 17th day onwards, whereas during the course of normal maturation it can be registered between 10th and 12th day [Figure 2],[Figure 3]. This means that there is a retardation of 5 to 7 days in the evolution of visual evoked cortical response in rabbit, maintained in total darkness. This retarded evolution progresses upto 21 days, parallel with the normal, and then there is a sharp decline to the extent that after 60 days no potential can be recorded with the technique applied [Figure 3].
Not only that, these potentials are replaced by the spontaneous activity of the brain with an augmented amplitude [Figure 2]. This spontaneous activity has some rhythmicity and is not modified by the photic stimulations. Similar phenomenon in kitten has been reported by Ganz. However, the electrical responses from lateral geniculate body and superior colliculi in these animals at this stage are normal in form and amplitude. This indicates that functional derangement due to lack of functional stimuli is mainly located in the visual cortex.
It is interesting to note that if these animals born and brought up in total darkness for 2 or 3 months, having no visual evoked cortical responses, are kept in natural conditions of enviromental illumination, there appear the electrical responses in the visual cortex in about 8 days, though with only half the amplitude as that of the normal and this does not improve later on.
Considering the biochemical parameters studied in visual pathways of animals born and brought up in total darkness, we have already reported that there is reduction in proteins percell in retina, lateral geniculate body and visual cortex, and the levels of RNA and DNA at 15 or 21 days are more close to that between birth and 8 days, that is, before the first opening of the eyes (Goswamy and Mandel  , Goswamy). Besides this, we note that total free nucleotides are lower than normal at 21 days in retina and visual cortex [Table 1] Similarly the synthesis of RNA from free nucleotides is lower than normal in the absence of light or the functional stimulus [Table 2].
The histoautoradiographic study [Figure 4] reveals that there is an over all increase of the radioactive uridine uptake in the retinal outer nuclear layer. This is due to a higher uptake of the precursor in the nucleotides and is comparable to normal 4 days, when the eyes are still not opened [Figure 1], meaning thereby, the evolution of RNA synthesis has not taken place and it has remained at level prior to opening of the eyes or the onset of functional activity. Further, it is obvious from [Figure 4] (0. G.) that there is little change in RNA synthesis throughout the course of maturation in the absence of light. However, the stimulation of right eye (O. D.) prior to enucleation definitely increased the RNA synthesis at each stage of development. This is more marked in animals maintained in total darkness than those in the normal conditions ( compare O.G. and O.D. in [Figure 1],[Figure 4].
From the above observations it may be said that the absence of visual stimuli since birth brings about electrophysiological and biochemical alterations in the functional maturation of visual pathways, which may become irreversible if the absence of functional stimuli is prolonged. These results may contribute to a better understanding of the mechanism of development of amblyopia of arrest and its sequelae, in cases devoid of adequate visual (functional) stimuli following congenital lens or corneal pathology.
I thank and highly appreciate the guidance and facilities provided to conduct this work by Profs. P. Mandel and P. Karli, and great help by Mme N. Bonaventure of centre de Neurochimie du C. N. R. S. at Strasbourg, France.
|1||BONAVENTURE N., GOSWAMY S. and KARLI P. (1967 - Maturation des potentiels ERG et evogues visuels chez le lapin eleve dans des conditions naturelles d'elairement ambiant' - C. R. Soc. Biol. (France). 161, No. 3, p. 689.|
|2||GANZ L. (1966) - Internatl. Gongr. of Psychology, Moscow - Symp. No. 15, P. 37.|
|3||GOSWAMY S., MANDEL P. and KARLI P. (1966) - 'Role of visual stimuli in the evolution of nucleic acids in visual pathways of young rabbits' - Presented at International. Symp. Ophthalmic biochemistry, Tutzing (W. Germany) and Publish in "Biochemistry of the eye" ed. by M.U. Dardenne and J. Nordmann; publisher, S. Karger, Basel (Switzerland), 1968, p. 514.|
|4||GOSWAMY S. (1967) - Thesis entitled "Role de L'eclairement ambiant dans la maturation de la retine et des voies visuelles chez le lapin: Aspects electrophysiologiques et biochimiques (Synthese des Acides nucleiques)", presented for the award of docteur es-sciences to the University of Strasbourg (France).|
|5||MANDEL P. and GOSWAMY S. (1966) - 'Quantitative estimation of nucleic acids in visual pathways of normal rabbits and variations during development - Orient. Arch. Ophthal - 4, p. 137.|
|6||MEJBAUM W. (1945) - Biokhimiyia - 10, p. 353.|