视光学基础-推荐下载

R e g n a O P T I C A LBASIC OPTICS MODULE 1 – VISION AND THE EYEVISIONACCOMMODATIONCORNEAIRISAQUEOUS HUMOUR LENSVITREOUS HUMOUR RETINAFOVEAOPTIC NERVE EMMTROPIA AMETROPIA MYOPIA HYPROPIA ASTIGAMATISM PRESBYOPIAVISIONVision is the ability of the human visual system to respond to light. Light is reflected from objects in the environment. The light is projected onto the retina in such a way that the brain is able to translate these nerve impulses into a visual image. Most people have normal vision and are able to see objects clearly with or without the aid of spectacles, however people with low vision or those who are blind are unable to see objects clearly, even with the aid of spectacles.When looking at an object in the distance (more than 6 metres away), the eye is relaxed and the light from the object is brought to a focal point on the retina. When looking at objects closer than 6 metres, the lens in the eye must change shape to enable the light to continue to focus on the retina. This change of shape of the lens is called accommodation. The ability to accommodate for near vision decreases throughout life, and at the age of 40 to 45, it has reduced to the level where most people cannot read without reading glasses.No accommodation is required to focusnear objects onto the Fovealight from distant objects onto the Fovea.The workings of the human eye are amazing and provide a range of functions, from being able to see very small objects, follow movement and accurately judge distances. The human eye can differentiate between shapes and colours, see varying amounts of light and operate under extreme temperatures.The visual system is a mass of extremely complex yet well organised parts, consisting of two eyes, nerve cells, nerve pathways, and a proportion of the brain.The eye works similarly to a camera in a number of aspects. The cornea and lens, together, form the main part of the optical system which focuses light onto the retina. The retina acts like a film of a camera, but unlike a film it processes the image and relays it to the brain through the optic nerve. In a real sense we see with out brain not our eyesThe eye is made up of the following major parts, each of which is explained briefly below.CorneaIrisAqueous Humour PupilCORNEALight rays that enter the eye are refracted (bent) by the cornea. The cornea provides some eighty percent of the eyes' refracting power. Rays then proceed to the lens to be further refracted. The lens has the ability to accommodate, changing the refraction to suit objects in the distance of at nearIRISThe IRIS is a coloured tissue which includes muscles. It is located behind the cornea and in front of the lens. It opens and closes to regulate the amount of light that enters the eye. The circular opening that it forms is called the PUPIL .AQUEOUS HUMOURThis is the clear liquid substance that fills the space between the cornea and lens.LENSThe lens is the only variable optical element in the eye. The lens can be made more bulbous, which needs to happen when a person looks at something close to them. This change enables light rays to focus onto the retina, when viewing a close object. The lens can change its’ focal power in a young person so that objects far away and as close as 10 cm can be seen clearly. As we get older, this ability is reduced until at about 40-45 years we need help in the form of reading glasses, to focus on objects that are near.VITREOUS HUMOURThis is a jelly-like substance which fills the centre of the eye.RETINAThe retina covers almost the entire inner surface of the eye. It is made up of three layers of nerve cells, including light receptors. The light receptors are know as rods and cones, which receive light and send information to the brain via the optic nerve fibres, which are long extensions of other retinal nerve cells.FOVEAThis is the area of greatest visual acuity (or clearest vision) which is located directly behind the pupil. When looking at an object, the reflected light from this object is focused onto the Fovea, and reflected light from everything else in the room falls onto other parts of the retina; the images from the other parts of the retina make up your peripheral vision.OPTIC NERVEThe optic nerve relays all messages from the retina to the brain. Where the opticnerve joins the retina an ‘optic disc’ is situated. This are has no rods or coneswhich makes it a blind spot. The persons particular blind spot is not noticed inday to day life as we learn to adapt with it, however every person has one in eacheye.EMMETROPIAThis is a word used to describe a normal visual condition. A person is called an Emmetrope when no form of visual correction is needed for distance viewing. The action of the eyes in this situation is shown in the diagrams above. For viewing objects at a distance of less than six metres, accommodation allows the person to view the object clearly.This is the “normal” situation for people who do not have to wear glasses. Just as in other parts of the body, there is variability in the size of the eye and its components. This variation makes for a range of optical defects.AMETROPIAThis word describes the collective group of visual defects (abnormal vision) resulting in a person needing some form of vision correction.The following sections briefly discusses the most common types of Ametropia and the lens types needed to correct these.MYOPIA (Short-sightedness)This describes the condition that occurs when the eye is looking at a distant object (more than 6 metres) in a relaxed state, and the light from the object is brought to a focal point in front of the retina (as 1. below). When this happens, the image on the retina will be blurred. Myopes are unable to improve their distance vision through changing their accommodation, but their near vision is usually good without the aid of spectacles.Vision without any correction.onto the Fovea.HYPEROPIA (Long-sightedness)This describes the visual defect that occurs when the eye is looking at a distant object in a relaxed state, and the light from the object is brought to a focal point behind the retina (as diagram 3. Below). This also causes blurred vision. Hyperopes are usually able to improve their distance vision through accommodation, however this often causes eye strain and/or headaches.Vision without any correction.light onto the Fovea.ASTIGMATISMAsigmatism is the visual defect that results in a blur in one direction or orientation. Astigmatism is often superimposed on short or longsightedness and is caused by the cornea of the eye having a shape which is not spherical but with variations in curvature in different directions. The problem can be corrected with a lens which has a corresponding but opposite variation in curvature to the cornea of the eye.Normal eye: Spherical corneaAstigmatic eye: Elliptical corneaPRESBYOPIAThis word is used to describe the visual defect which causes blurred vision in the near only, and is as a result of degenerating muscles and lens in the eye. This defect generally becomes noticeable at the age of 40 to 45 and becomes more evident as one ages. Presbyopes require near vision correction amd may also require correction for myopia, hyperopia and/or astigmatism, with all human beings becoming presbyopic at some stage.Presbyopia Corrected Presbyopia。

眼视光学基础知识一．定义1.正视眼：当眼调节静止时，外界的平行光线(一般认为来自5m以外)经眼的屈光系统后恰好在视网膜黄斑中心凹聚焦，这种屈光状态称为正视。

2.非正视眼：当眼调节静止时，外界的平行光线经眼的屈光系统后，若不能在视网膜黄斑中心凹聚焦，将不能产生清晰像，称为非正视或屈光不正。

A．近视：当眼调节静止时，外界的平行光线经眼的屈光系统后成像在视网膜前面，典型的近视表现为视远模糊视近清晰。

近视一般分为两类，即生理性近视和病理性近视。

近视眼矫治应用合适的凹透镜或类同凹透镜的原理和方法，使平行光线发散，进入眼屈光系统后聚焦在视网膜。

矫治的原则是最好矫正视力，最低矫正度数。

(一)按近视的程度分类：1. ≤-3.00 D，为低度近视；2. -3.25 D至~6.00 D为中度近视；3. - 6.25 D至~10.00 D为高度近视；4. -10.00 D以上为重度近视(二)按屈光成分分类1.屈光性近视。

2.轴性近视。

B. 远视：当眼调节静止时，外界的平行光线经眼的屈光系统后成像在视网膜后面。

□远视的原因是眼轴相对较短或者眼球屈光成分的屈光力下降。

可能是生理性的原因，如婴幼儿的远视；也可能是一些疾病通过影响以下两个因素而导致远视：①影响眼轴长度：眼内肿瘤，眼眶肿块，球后新生物，球壁水肿，视网膜脱离等等；②影响眼球屈光力：扁平角膜，糖尿病，无晶状体眼等等。

□远视者能清晰聚焦远处物体的远视眼，不同于近视，一些远视患者能看清楚远处物体，即能使远处物体清晰聚焦在其视网膜上。

这是因为，远视者可以通过自己的调节使外界平行光焦点前移至视网膜上，从而获得较清晰的远距离视力。

□.远视者的视觉疲劳远视者为了清晰聚焦，在看远时就动用了调节；看近时，则需付出更大的调节量。

因此，远视者调节从未放松过，而且在看近时使出比其他正视或近视者更多的调节，即很多时候他们都处于过度调节状态，容易产生视物疲劳□远视者远视度数随年龄变化。

某些远视者年轻的时候视力很好，在年纪稍大的时候“变”成了远视。