With age comes the loss of the flexibility of the lens, and a form of farsightedness called presbyopia results. The lens is operated by muscles that stretch it flat or allow it to thicken, changing the focal length of light coming through it to focus it sharply on the retina. ![]() The lens is dynamic, focusing and re-focusing light as the eye rests on near and far objects in the visual field. The main function of the lens is to focus light on the retina and fovea centralis. In conditions of low light, the iris relaxes and the pupil enlarges. In conditions of high ambient light, the iris contracts, reducing the size of the pupil at its center. The iris, which is conspicuous as the colored part of the eye, is a circular muscular ring lying between the lens and cornea that regulates the amount of light entering the eye. The cornea, the front transparent layer of the eye, and the crystalline lens, a transparent convex structure behind the cornea, both refract (bend) light to focus the image on the retina. It passes through other layers that process it so that it can be interpreted by the retina (Figure 1b). But light does not impinge on the retina unaltered. The photoreceptive cells of the eye, where transduction of light to nervous impulses occurs, are located in the retina (shown in Figure 1) on the inner surface of the back of the eye. Please get in touch for more information.The human eye is an organ that reacts with light and allows light perception, color vision, and depth perception. In addition to high-end quality lenses, an inverter and a BIOM, are used for fundus observation.įor fundus observation devices adaptations, OM-19 is compatible with Oculus BIOM and Haag Streit EIBOS. We are able to observe the retina thanks to the cutting-edge Takagi OM-19 Operating Microscope, that uses exceptional quality objective lenses and eyepieces made in Japan. The video showcases the incredible retina, just before a vitreoretinal surgery procedure, where the optic disc that connects to the optical nerve and the blood vessels are visible. In this video, we can observe another way of visualising the retina, with an operating microscope. But we will talk more on the most common retinal diseases in our future posts. ![]() Ophthalmologists and optometrists examine the retina in order to detect signs of damage or abnormalities, which could cause retinal diseases. There are a few ways to examine the retina, by using different devices such as an ophthalmoscope, a slit lamp, a retinal camera or an OCT, for a distinct view of the retina’s layers. One of the nerve fibres in the ganglion cells called axon, together with glial cells forms the optical nerve, which transmits the visual signals to the brain. Based on their location in the retina, these cells can receive inputs from 100 rods and cones. At this stage the ganglion cell, another type of neuron, once the information has been received from the photoreceptors, it transmits it to the brain through the optical nerve. The bipolar cells are a type of neuron that connects the rods and cones with the ganglion cells, this is called synaptic connection. For this reason, looking at an object in the dark, it’s easier to focus if looking slightly to the side of the object and not directly at it. The peripheral part of the retina is composed of approx. This allows the human eye to achieve a sharp and visually detailed colour vision, crucial for reading for example. Whereas, the most important one part of the macula is its centre called the fovea, where the highest concentration of cones are located. The part with a high concentration of cones is called the macula, which is around 5.5mm. 7 million cones located predominantly in the central part. ![]() These retinal layers are connected by synapses and supported by the outer layer of pigment epithelium which provides nutrients to the retina. Reception of light rays, transmission to the bipolar cell layer and ganglion cell layer and finally transmission through the optic nerve. It’s made of neuron layers that can be divided into 4 main groups based on the stages of processing the light that enters the eye, as such: The retina in human adults is 0.5mm thick and 22mm in diameter and is considered to be the most important part of the eye. However, the retina and the camera sensor, both play the same role in transforming light photons into electrical impulses. The impressive layers of tissue that form the retina are more complex than any camera sensor on the market, be it an analogue film or digital CCD/CMOS sensor. Now we are going to focus on the retina and its functions. In our previous post, we have introduced the main similarities between the eye and the camera. Retina and Its Functions – The Role of 150 Million Receptors and 1 Million Optic Nerve Fibres
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