DONE BY : 1- FATIMA HAMAD ALDHAHERI

2- MARIAM ESSA ALABRI

HUMAN EYE Project

Topics that will be covered

General Information about Eye’s

how does the eye work analogous to a camera. The Camera and the Eye

Describe three vision defects Nearsightedness Farsightedness and Astigmatism

Explain which kinds of lenses are needed to correct the previous vision defects. Lenses picture. Correction of Common Vision Defects

General Information about Eye’s

Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement. In higher organisms the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system Image-resolving eyes are present in molluscs, chordates and arthropodsThe simplest "eyes", such as those in microorganisms, do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment.

how does the eye work analogous to a camera ?

How Does The Human Eye Work?

The individual components of the eye work in a manner similar to a camera. Each part plays a vital role in providing clear vision. So think of the eye as a camera with the cornea, behavingmuch like a lens cover. As the eye's main focusing element, the cornea takes widely divergingrays of light and bends them through the pupil, the dark, round opening in the center of thecolored iris. The iris and pupil act like the aperture of a camera.

Next in line is the lens which acts like the lens in a camera, helping to focus light to the backof the eye. Note that the lens is the part which becomes cloudy and is removed during cataractsurgery to be replaced by an artificial implant nowadays. 

The very back of the eye is lined with a layer called the retina which acts very much like the film The retina is a membrane containing photoreceptor nerve cells that linesthe inside back wall of the eye of the camera.

The photoreceptor nerve cells of the retina change the light rays into electrical impulses and send them through the optic nerve to the brain where animage is perceived. The center 10% of the retina is called the macula. This is responsible foryour sharp vision, your reading vision. The peripheral retina is responsible for the peripheralvision.

As with the camera, if the "film" is bad in the eye (i.e. the retina), no matter how good the rest of the eye is, you will not get a good picture.

The human eye is remarkable. It accommodates to changing lighting conditions and focuses light rays originating from various distances from the eye. When all of the components of the eye function properly, light is converted to impulses and conveyed to the brain where an image is perceived.

The Camera

The Eye

how does the eye work analogous to a camera ?

The Camera and the Eye Images are formed in a camera by refraction in a

manner similar to image formation in the eye. However, accommodation to image closer objects is done

differently in the eye and camera.

Common Vision Defects

Nearsightednessor Myopia

Myopia "nearsightedness" (AmE), "shortsightedness" (BrE) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it. This causes the image that one sees when looking at a distant object to be out of focus but in focus when looking at a close object.

farsightedness

Hyperopia, also known as farsightedness, longsightedness or hypermetropia, is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or the lens cannot become round enough), causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance. As an object moves toward the eye, the eye must increase its optical power to keep the image in focus on the retina. If the power of the cornea and lens is insufficient, as in hyperopia, the image will appear blurred.

Astigmatism

Astigmatism is an optical defect in which vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina. This may be due to an irregular or toric curvature of the cornea or lens. There are two types of astigmatism: regular and irregular. Irregular astigmatism is often caused by a corneal scar or scattering in the crystalline lens and cannot be corrected by standard spectacle lenses, but can be corrected by contact lenses. Regular astigmatism arising from either the cornea or crystalline lens can be corrected by a toric lens. A toric surface resembles a section of the surface of an American football or a doughnut where there are two regular radii, one smaller than the other one. This optical shape gives rise to regular astigmatism in the eye

Astigmatism

lenses are needed to correct the vision defects.

Nearsightedness farsightedness Astigmatism

Eye care professionals most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery

an eye doctor may provide the patient with an eyeglass prescription for corrective lenses.Minor amounts of hyperopia are sometimes left uncorrected. However, larger amounts may be corrected with convex lenses in eyeglasses or contact lenses. Convex lenses have a positive dioptric value, which causes the light to focus closer than its normal range.

Astigmatism is corrcted by an asymmetric lens to compensate for the asymmetry of the eye’s lens

lenses are needed to correct the vision defects.

Nearsightedness farsightedness Astigmatism

Correction of Common Vision Defects