Vision helps us to see the beauty of the world or recognize the approaching danger. Eyesight is a vitally important part of human sensory system. It is of paramount importance for studying, work, social networking and other parts of life. Eyesight deterioration leads to significantly lower quality of life, while its loss is a disability making people dependent on the others in many ways.
Causes of ophthalmic diseases can be divided into two categories:
- eye optic system diseases (the system through which the light passes, including cornea, crystalline lens and vitreous body)
- eye sensory system diseases (the system responsible for perception of the light and its transformation into the stream of nervous impulses to be transmitted to the brain (retina and optic nerve)
Modern ophthalmology has reached great success in treatment of the diseases affecting optic system of the eye. At the same time, treatment effectiveness in eye sensory system diseases is quite low. One of the most common causes of eyesight deterioration in senior age is age-related retinal degeneration (ARRD), and it affects sensory system of the eye. ARRD can be triggered by glaucoma, diabetes mellitus and other diseases.
In order to understand how stem cells can help in ARRD treatment, it is necessary to know retinal composition and function. Photoreceptors of the retina function as light sensors, while its neurons process information received from photoreceptors and transmit neural impulses to the appropriate areas of the brain.
Retinal neurons responsible for receptors data transmission to the brain are called retinal ganglion cells (RGCs). RGCs processes transmitting data to the brain form optic nerve. Thus, damage of RGCs or their processes leads to the progressive eyesight deterioration even in cases when eye optic system is unaffected. Unfortunately, RGCs own regeneration potential is quite limited, which means that in case of damage the probability of functional restoration of the cells is quite low, therefore age-related retinal degeneration is a progressive condition.
However, scientific research has demonstrated markedly increased regeneration capacity of RGCs with specific stimulation. Regeneration is facilitated by biologically active substances produced by stem cells, such as nerve growth factor, brain-derived neurotrophic factor etc. These biologically active substances produced by stem cells are called neuroprotectors. They can be synthesized by different types of stem cells, however the most effective in this case are neural stem cells.
Studies have shown that administration of neural stem cells significantly increases regeneration of RGCs processes making the optic nerve. In order to take advantage of neuroprotective effect of stem cells, they are administered inside the vitreous body, closer to the retina. This enables transfer of neuroprotective substances into the retina and restoration of the damaged RGCs. This approach allows for inhibition of the disease progression, though the dead RGCs are not replaced with the new ones because migration of stem cells from the vitreous body inside the retina is difficult.
In order to overcome this limitation, it is possible to combine this method (intravitreal administration) with subretinal administration of stem cells. This makes migration of stem cells into the retina easier, and, in case of successful engraftment, these stem cells can replace the dead RGCs.
Thus, treatment with neural stem cells gives hope for inhibition of the disease progression and eyesight improvement in patients with age-related retinal degeneration and other diseases of eye sensory system.