Biomedical subjects

K Pendrak

Publications and source records attributed to K Pendrak.

4 recordsLinked to original sources

PubMed2000

Choroidal vascular permeability in visually regulated eye growth.

The choroidal thickness fluctuates both diurnally and in response to changes in visual input. The fluctuations may represent a physiologic means of aligning the retinal photoreceptors with the focal position of distant images during the emmetropization process. To evaluate the basis for choroidal thickness changes, we studied the sources of the extravascular fluid in the chick choroid in two visually-regulated ocular growth conditions: accelerated ocular growth in goggle-induced form-deprivation myopia and ocular growth retardation in the recovery from myopia after goggle removal. Two week old chicks, controls, myopic and those recovering from myopia, received fluorescein dextran (MW = 140,000) as a tracer. It was given by intravenous injection to identify a potential vascular pathway and by intracameral injection to identify a potential pathway from the anterior chamber to the suprachoroidal space. Using a microscopically positioned needle, clear fluid was aspirated from the suprachoroidal space of the enucleated chick eye; this fluid presumably corresponds to the contents of the lacunae, prominent lymphatic-like structures of the chick choroid. Plasma, aqueous humor and suprachoroidal fluid were sampled 1 hr after injection and assayed for both protein content and the tracer dye. Sulfated glycosaminoglycans were assayed in the suprachoroidal fluid, choroid and sclera under each experimental condition. In control chicks, aqueous humor and suprachoroidal fluid protein concentrations were about 0.8 and 9% of plasma levels respectively. Aqueous humor protein concentration was unaltered in myopic or recovering eyes. Suprachoroidal fluid protein concentration in myopic eyes fell dramatically to 1.5% of plasma levels (P < 0.001). In contrast, recovery from myopia led to a marked increase in suprachoroidal fluid protein level to 30% of that in plasma (P < 0.001). None of the procedures affected suprachoroidal fluid protein in the contralateral control eyes. In all three groups of chicks, fluorescein dextran distribution in the suprachoroidal fluid at 1 hr after intravenous injection tracked protein levels, with reduced levels in myopic eyes and elevated levels in recovering eyes. After intracameral injection, suprachoroidal fluid dextran levels were higher in injected eyes of control chicks (P < 0.01) and in recovering eyes (P < 0.001) but lower in myopic eyes (P < 0.01), compared to the levels in the respective contralateral non-injected eyes in each group. Sulfated glycosaminoglycan levels were at the limits of detection in the suprachoroidal fluid under all conditions and, on a whole choroid basis, were unaltered in the choroid in either myopia or recovery. Suprachoroidal fluid is lymph-like in nature and largely derives from plasma. Sulfated glycosaminoglycan levels do not seem to regulate the fluid content of the choroid in either myopia or recovery. Instead, the changes in protein and marker dye levels in myopic and recovering eyes suggest markedly altered choroidal circulatory dynamics and capillary permeability in both conditions.

Animals↗

PubMed1998

Induction of axial eye elongation and myopic refractive shift in one-year-old chickens.

Depriving the eyes of neonatal animals of form vision induces axial eye elongation and ipsilateral myopia. We studied one-year-old chickens, an age at which full body growth has been attained, to learn if form deprivation myopia can develop at a later stage. We found that ocular reactivity to visual form deprivation continues in one-year-old chickens; but both the growth stimulation and the myopic shift in refraction are attenuated compared with newly hatched birds. Neurochemical changes in visually deprived eyes of one-year-old chickens parallel those in newly hatched chicks: ipsilateral decreases in retinal dopamine and in the activity of ciliary ganglion and uveal choline acetyltransferase. These findings strengthen the relevance of the form deprivation model to more common human myopia and suggest a common eye growth control mechanism at both ages.

Aging↗

PubMed1997

Retinal dopamine in the recovery from experimental myopia.

PURPOSE: To address further a possible role for retinal dopamine in postnatal eye growth, we studied the response of retinal dopamine in eyes of chicks recovering from myopia. METHODS: Newborn chicks either received a unilateral translucent goggle to induce form deprivation myopia or were reared with unimpaired visual input. The goggle was removed from half of the chicks on day 7. Myopic, recovering and control never-goggled chicks were studied on days 7, 9 and 14. Eyes were enucleated postmortem and measured in axial and equatorial dimensions with calipers. Retinal levels of dopamine and its principal metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were assayed by high performance liquid chromatography with electrochemical detection. RESULTS: Compared to contralateral and control eyes, retinas of goggled eyes at each time point had reduced levels of dopamine and DOPAC and a lowered calculated DOPAC/dopamine ratio, an index of dopamine metabolism. In eyes recovering from myopia, all biochemical parameters showed prominent increases by 2 days after goggle removal and had reached the level of both contralateral eyes and control eyes by one week after goggle removal. As evidence of a contralateral effect, the retinas of open eyes of chicks wearing a unilateral goggle demonstrated equal dopamine levels but reduced DOPAC compared to eyes of never-goggled chicks. CONCLUSION: An early rise and eventual normalization of retinal dopamine, DOPAC and the DOPAC/dopamine ratio correlate with recovery from myopia. Combined with recent results from lens rearing experiments, these findings suggest that dopaminergic amacrine cells may participate in visually guided eye growth regulation and not just in the myopia response to visual form deprivation. The retinal biochemical alteration in eyes contralateral to a goggle identifies a previously unappreciated binocular interaction in the chick.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1995

Ciliary ganglion choline acetyltransferase activity in avian macrophthalmos.

While present evidence fails to support an etiologic mechanism for myopia based on accommodation or choroidal blood flow, atropine exhibits anti-myopia activity in many species. Accordingly, we studied choline acetyl transferase (ChAT) activity in the ciliary ganglion, uvea and retina of chicks with experimental macrophthalmos to identify a potential pathway for the moderation of eye growth by cholinergic neurons. Following unilateral lid suture or goggle, chicks were reared for 1 week under one of four lighting conditions known to induce macrophthalmos or myopia. Ocular tissues and ciliary ganglia were assayed for ChAT activity by measuring the conversion of 14C-acetyl CoA to 14C-acetylcholine. For some chicks, the goggles were removed at 1 week, and ChAT activity was measured 2 or 7 days later. Depending on the rearing condition, ciliary ganglion ChAT activity was depressed from 16 to 28% ipsilateral to the lid suture; enzyme activity also was reduced in the choroid of visually deprived eyes under most conditions. In contrast, lid suture resulted in no consistent trend in ChAT activity in either the anterior uvea or retina. For chicks wearing a unilateral goggle and reared under a 12:12 hr light/dark cycle, ChAT activity was depressed in the ciliary ganglion, anterior uvea and choroid on the visually deprived side. Following goggle removal to allow recovery from myopia. ChAT activity in the ciliary ganglion and uvea was returned toward that of the control side. The ciliary ganglion may participate in a neural pathway influencing the development of form-deprivation myopia.

Animals↗