Convex lens focuses light rays
• Concave lens diverges light rays
reduced eye
• reduced eye” :it is considered to be a single refractive surface, with its central point about 20 millimeter in front of the retina and a total refractive power of 59 diopters.
Sense organs
Wen-jun Xin xinwenjun2002@
Introduction
• Why did studied this chapter? • Classification:
Basic concepts
• 1: the concept of receptor or sense organs: • The special structure or device, which localized in the skin or organs, can sense the change of external world or internal enviroment. • Classification by the structure: the end of axon; Capsule-like structure; sense organ • classification by the character of stimulus: mechanoreceptor; chemoreceptor; thermoreceptor and opticreceptor • Classification by localazation: externalreceptor; internalreceptor and proprioceptors
Diameter of the pupil
• 1: The pupil controls the quantity of light entering the eye;. • 2: The pupil of human eye can become as small as about 1.5 millimeter and as large as 8 millimeter in diameter. • 3: When the people went into the darkness, the diameter of pupil become large and allow more lights into the eye.
1、晶状体折光能力的调节
① 视远物时，睫状肌弛缓，睫 状小带被拉紧，使晶状体被牵 拉而呈扁平。视近物时，通过 反射使睫状肌收缩。
② 睫状肌受动眼神经中副交感 神经纤维支配。晶状体的这种 改变增加了它的折光能力，使 近处的辐散光线仍能聚焦在视 网膜上形成清晰的物象。
③ 晶状体的弹性随年龄的增大 而减小，
Visual sense organ
• The common activities of eye, optic nerve and optic cortex formed Vision
• The basic structure of eye • Eye is affiliated organ of visual system, including dioptric system (cornea, aqueous humor, lens and vitreous humor) and photographic system (retina and optic nerve fiber) • The adequate stimuli is Electromagnetic waves, its wavelength 380-760nm .
• Transduction: receptor can conversed the energy of stimulus into the electric energy of action potential. • Receptor potential and generator potential • Both is Slow potential transitional, like end-plate potential.
•
The encoding of receptor
• 编码作用是指感受器把刺激包含的环境变 化的信息转移到了新的电信号系统即动作 电位的序列之中。 • ① 外界刺激质的编码 ② 外界刺激“量”或“强度”的编码 信息每通过一次神经元间的传递，都 要进行一次再编码
Adaptation of receptor
（二）简化眼 简化眼是假想的人工模型，其光学参数与正常眼等值。简化眼 模型假设眼球为一单球面折光体，前后径为20mm，折光指数为 1．333，节点(n)距角膜前表面5mm，后主焦点正好在简化眼的 后极，相当于视网膜的位置
简化眼的用处
• 利用简化眼可以算出正常人眼所能看清的物体 的视网膜像大小的限度。检查证明，正常人眼 即使在光照良好的情况下，如果物体在视网膜 上成像小于５μm，一般就不能引起清晰的视觉。 这说明，正常人的视力或视敏度（visual acuity）有一个限度 。要表示这个限度，只能 用人所能看清的最小视网膜像的大小来表示， 而不能用所能看清的物体大小来表示，因为物 像的大小不仅与物体的大小有关，也与物体与 眼之间的距离有关。人眼所能看清楚的最小视 网膜像的大小，大致相当于视网膜中央凹处一 个视锥细胞的平均直径
2: Refraction of light at an interface betweif light rays traveling enter another interface in different angle.
Application of refractive principles to lenses
General properties of receptor
• 1: adequate stimulus: • It is common properties, every receptor have its own most sensetive stimuli.
The transduction and receptor potential
The lens system of eye
• The refraction principles
Physical principles of optics
• 1:Refraction of light: the ratio between velocity of light in air via the velocity in the substance. • Such as: light travel through a glass from air. •
• The sensitivity of receptor to adequate stimulus with continued unchanged intensity attenuated. • The mechanism is frequency of action potential on fiber decreased • 1) rapidly adapting receptor and slowly adapting receptor
视角的倒数表示视 力（视敏度）
Regulation of eye
• Accommodation of lens: • Diameter of the pupil • Convergence
Mechanism of accommodation
• the lens`s shape can change from a moderately convex lens to a very convex lens, so the refractive power of the lens of the eye can be increased voluntarily from little diopter to great diopter. This is called accommodation of eye. • How to accommodated the diopter of the lens. • 1: when we have a distant vision, suspensory ligaments pulled the lens edges toward the outer circle of the eyeball. The tension on the ligaments causes the lens to remain relatively flat. • 2: when we have a near vision, suspensory ligaments is relaxed, because of the natural elasticity of the lens capsule, the lens assumes a more spherical shape.
• 散光：正视眼折光系统的折光面(角膜和晶状 体)呈球面，即折光面每一个方向的曲度都是 相等的，有共同的焦点。如果折光面每一个方 向的曲度不等，则通过此折光面上各个不同曲 度的部分的光线就不能在同一平面上聚焦：凡 经过曲度较大的部分的光线将聚焦于视网膜之 前；凡经过曲度较小的部分的光线将聚焦于视 网膜之后；只有经过曲度正常的部分的光线才 聚焦在视网膜上。因此，视网膜上不能形成清 晰的像，这种屈光不正称为散光。散光多见于 角膜表面的曲度异常，较少由晶状体表面的曲 度异常所致。散光眼可用适当的柱镜片矫正， 使曲度过大的部分的折光能力减小，而使曲度 过小的部分的折光能力增加。