Eye Dork - Eye Have the Answer

For vision to be a continuous process the photoreceptors (rods and cones) must continually regenerate 11-cis retinal. Rods and cones have slightly different ways of doing this. WARNING: this is only for the extremely nerdy. If you aren't very interested in the biochemical processing of vitamin A in the retina, this entry probably isn't for you. For rods: A photon (light ray) is absorbed by pigment within the opsin in the outer segment of the photoreceptor cell. Inside the activated opsin, 11-cis retinal is converted to all-trans retinal and released to the disc of the inner segment of the photoreceptor. Within the disc, all-trans retinal binds phosphatidylethanolamine. This produces N-retinylidine-phosphatidyl-ethanolamine (NRPE). ATP binding cassette transporter carries the NRPE complex to the cell membrane of the disc. At the cell membrane the all-trans retinal portion of the NRPE complex is transported to the cytoplasm within the cell body of the photoreceptor. Insi...

Light rays from an image are focused onto the retina by glasses or contacts and the anterior structures of the eye. Light rays are converted from a physical wave into a chemical and electrical message to be interpreted by the brain. This process is called phototransduction. In the sensory retina, there five main cell types and nine layers involved in this process. The sensory retina is an optically clear structure. For phototransduction to begin, an image must pass through the anterior blood supply and every layer of the sensory retina until the image finally reaches the photoreceptor layer. The photoreceptor layer is composed of rods and cones. There are roughly 120 million rods in the adult retina. These cells allow us to see the difference between light and dark. Rods are utilized for night vision and low lighting conditions. There are 6 to 7 million cones in the adult eye. Cones are only utilized for day or brighter conditions. These cells are specialize for color detection. ...

The main purpose of the front half of the eye is to focus a clear image on the retina. The next step in the process of vision is to convert that visual information (light rays) into a chemical message for the brain to process. However, before the image reaches the retina, it must first pass through a jelly-like substance called the vitreous. The vitreous fills most of the volume of the eye. It is mostly composed of water, but can also contain salt, sugar, a collagen called vitrosin, hyaluronic acid and other various proteins. When all these components are spaced out uniformly the vitreous remains clear and images pass on through to the retina undisturbed. With time more water concentrates in the lower portion of the eye. This leaves more proteins in contact with one another in the superior portion of the eye. The positive and negative charges of the molecular components of these proteins attract one another and result in the various proteins clustering together. This clustering cre...

My favorite part of each eye exam is getting the slit lamp (microscope) out and studying the various structures of a patient's eyes. The eye is a structure with many beautiful features. Each component of the eye plays a role in capturing images from the external environment and preparing that visual information for its journey through the brain. The first structures examined are the eyelids and eyelashes. These structures work to protect the eye from debris in the air and reset the tear film with each blink. A major contributor to our natural tears, the meibomian glands, are located just behind the eyelashes. Our major concern when looking at the eyelid are various skin cancers (basal cell carcinoma, squamous cell carcinoma, sebaceous gland carcinoma). Past the eyelids the tear film is observed. The tear film lubricates and protects the front surface of the eye, the cornea, and plays a vital role in keeping images clear on the way to the retina. The tear film is composed of thr...