生理学的概念及生命活动的特征 (35).ppt

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1、 Visual function of the eyeChapter 09010203The accommodation reflexRefractive system of the eyeAmetropiaOptics of the eyeThe accommodation reflex02When the normal adult eye is unmodulated,the posterior principal focus of the refractive system is positioned on the retina;rays from objects up to 6 met

2、res away can be considered parallel,so these rays can form a clear image on the retina.The accommodation reflexWhen looking at near objects within 6m,the light emitted from the object is radiant.If the refractive power of the eye remains unchanged,theoretically the object should be imaged behind the

3、 retina,resulting in blurred vision,but the normal eye can see near objects clearly,which is the result of proper adjustment of the refractive power of the eye.02The accommodation reflexThe near reflex and pupillary light reflex The near reflex of the eye:1)Convexity of the lens,2)Near reflex of the

4、 pupil,3)convergence reflex.021)Convexity of the lens The primary adjustment of the eye when looking at close objects is the convexity of the lens.1)Convexity of the lens As there is a limit to the elastic deformation of the lens,there is also a range in the eyes ability to see near objects.The maxi

5、mum accommodation of the lens can be expressed as the closest distance at which the eye can clearly see an object,which is called the near point.1)Convexity of the lens The near point can move further away with age.Age 10,9cm;Age 20,11cm;Age 60,83.3cm In older people,the lens becomes less elastic an

6、d harder,resulting in a reduction in the eyes ability to adjust,which is called presbyopia.presbyopiapresbyopiaPresbyopic eyes are more distant at the near point than normal eyes,but the far point is normal.2)Near reflex of the pupilThe pupil is the hole in the middle of the iris,which is the gatewa

7、y for light to enter the eye and can vary in diameter from 1.5 to 8.0mm.When looking at a near object,it reflexively causes the pupils of both eyes to narrow,which is called the pupillary near reflex.The significance of this reflex is to reduce the spherical and chromatic aberrations of the refracti

8、ve system,resulting in a clearer retinal image.2)Near reflex of the pupil3)convergence reflexWhen the eyes look at a near object or when the object being looked at is moved closer from a distance,the visual axes of the two eyes converge towards the nasal side,which is called the convergence reflex.T

9、he effect of the convergence reflex is that when both eyes look at a near object at the same time,the image of the object can still fall on the symmetrical point of the retina of both eyes to avoid the formation of diplopia.3)convergence reflexThe pupil-to-light reflex is a process in which the pupi

10、l narrows when exposed to strong light and dilates when the light becomes weaker.Its significance is to regulate the amount of light entering the eye so that the retina is not damaged by too much light and the vision is not affected by too little light.The pupillary light reflex is bilateral,with th

11、e pupils of both eyes narrowing when light is shone on one side of the pupil,so it is also known as the reciprocal light reflex.The pupil-to-light reflexThe centre of the pupillary light reflex is located in the midbrain,so it is often used clinically as an indicator of the depth of anaesthesia and

12、the criticality of the condition.The pupil-to-light reflexThe distance that the normal eye can see an object.03 AmetropiaIf the refractive power of the eye is abnormal,or the morphology of the eye is abnormal,so that parallel light rays cannot be focused on the retina of the quiet unadjusted eye,the

13、 eye is said to be ametropia.There are three types of refractive errors,namely myopia,hyperopia and astigmatism.Ametropia1）myopiaMyopia means that objects at a distance are not seen clearly and can only be seen clearly when they are closer to the eye.Myopia can be caused by a long anterior-posterior

14、 diameter of the eye or a refractive system with too much refractive power,which can be corrected with concave lenses.1）myopiaMyopia can be corrected by wearing concave lenses.Hyperopia is caused by the short anterior-posterior diameter of the eye or the weak refractive power of the refractive syste

15、m,which means that parallel light from distant objects is focused at the back of the retina and therefore does not form a clear image on the retina.2）HyperopiaHyperopia,which requires adjustment when looking at both distant and near objects and therefore tends to cause fatigue and even headaches whe

16、n reading for long periods of time,may be corrected with a convex lens.2）Hyperopia2）HyperopiaStudies have found that all infants and children up to the age of six have varying degrees of hyperopia.Hyperopia can be corrected by wearing convex lenses.The surface of the cornea of the normal human eye i

17、s orthospheric,with equal curvature at each meridian of the sphere,so that the parallel rays arriving at each point on the surface of the cornea are refracted and focused on the retina.3）Astigmatism3）AstigmatismAstigmatism is mainly due to the different radii of curvature of the corneal surface,so p

18、arallel light rays cannot be focused on the retina,resulting in blurred vision or distortion of the object.Regular astigmatism can usually be corrected with a cylindrical lens.3）AstigmatismThe accommodation reflexRefractive system of the eyeAmetropiaThe main contents we have studied are as follows：ThanksThanks