Disorders of eye.pptx myopia hypermetropia

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1. P H YSI O L O G Y O F EYE

2. O u t l i n e 2 Functional structures of the eye Image-forming mechanism Visual pathway Abnormalities of vision

3. ▶ T h e e y e i s m o ve d w it h i n t h e o r b it b y six e x tr a o cu la r m u scle s. ▶ F o u r r e ct u s m u sc l e s c o n t r o l e y e b a l l m o v e m e n t i n p e r p e n d i cu l a r axes. ▶ T w o o bl i q u e mu sc l e → t ra n s i t i o n a l ro t a t i o n o f e ye T h r e e cr a n i a l n e rv e s a re c o n c e r n e d w i t h e y e b a l l movements O c u l o m o t o r : s u p e r i o r r e ct u s , m e di a l r e ct u s, i n f e r i o r r e ct u s & i n f e ri o r O b li q u e T ro c h l e a r : s u p e r i o r O b li q u e A b d u c e n s : l a t e ra l r e ct u s E x t r aocul a r mus c le 15

4. emedicine.medscape.com/article/1189759-overview I O S R I O / S R S R / I O S R I O L R M R M R L R S O I R S O / I R I R / S O I R S O M R M R C O N V E R G E N C E

5. Corneal reflex 26 ▶ It is a protective reflex shutting of the eye by its lids on touching the cornea Components of Corneal reflex ▶ Receptor: corneal receptor. ▶ Afferent nerve: ophthalmic division of trigeminal nerve→ trigeminal ganglion →trigeminal nucleus in pons. ▶ Center: superior colliculus ▶ Efferent: Facial nerve ▶ Effecter: orbicularis oculi muscle ▶ Result: shutting of the eyelids.

6. 27 ▶ i s a c o mmo n c o nd i tio n i n w hi c h the c urv a t u r e o f t h e c o r n e a i s n o t u ni f o rm. ▶ too great a curvature of the cornea in one plane of the eye. ▶ B l urred v i s i o n, u s u a l l y c a u s ed by a n une v en ( n o n s pheri ca l ) c o n t o ur o f t h e c o r n e a . ▶ Corrected with prescription glasses (cylindrical) lens Astigmatism

7. ▶ Avascular, biconvex structure ▶ E n c l o s e d i n e l as t i c capsu l e ▶ L i e s d i r e c t l y b e h i n d t h e i r i s a n d pu p i l ▶ Lens is a flexible t r ans p a r en t bod y w i t h a n a t u r a l l y r ounded shape ▶ Th i s t r an s par en t s t r u c t ur e ( c r y s t al l i n e l e ns ) h e l d i n p l ac e b y a c i r c u l a r le n s ligament ( zonule ). le n s 28

8. Pupillary light Reflexes 33 ▶ When light is directed into one eye, the pupil constricts ( pupillary light reflex ). ▶ The pupil of the other eye also constricts ( consensual light reflex ). ▶ It is initiated by visual photoreceptors (cones & rods) ▶ Imp u l s e s re l a y e d by b i po l a r c e ll s → g ang li o n c e l l s of ret i n a → discharged to optic nerve. ▶ Partial crossing of optic nerve occurs at optic chiasma with subsequent formation of optic tract. ▶ The optic nerve fibers that carry the impulses initiating these pupillary responses leave the optic nerves near the lateral geniculate bodies. ▶ On each side, they enter the midbrain via the brachium of the superior colliculus and terminate in the pretectal nucleus .

9. Pupillary light Reflexes cont’d… 34 ▶ From this nucleus, the axons of pretectal nucleus project to the ipsilateral Edinger–Westphal nucleus and the contralateral Edinger–Westphal nucleus. ▶ The fibers from this nucleus proceed as the oculomotor nerve till reaching the orbit. ▶ The preganglionic fibers relay in the ciliary ganglion ▶ The postganglionic fibers (short ciliary nerves) pass from this ganglion to the ciliary body. ▶ This pathway is dorsal to the pathway for the near response. ▶ Effectors: circular muscle in iris ▶ Result: pupillary constriction

10. The iris constricts or dilates to adjust size of the pupil. The pupil allows light to enter the posterior segment of the eye.

11. Abnormality of pupil 36 A r g y ll R o b e r t s o n p u p il = ▶ If n o p up i l l a r y l i g ht r e s p o n s e ▶ T he p u p il i s s m a l l i n d i m l i gh t ▶ D o e s n o t co n s t ri c t fu r t h e r w h e n e y e i s e x p o s e d t o b r i gh t light ▶ Occur example in neuro- syphilis

12. THE IMAGE-FORMING MECHANISM 37 ▶ The eyes convert energy in the visible spectrum into action potentials in the optic nerve. ▶ The wavelengths of visible light range from approximately 397 nm to 723 nm. ▶ The images of objects in the environment are focused on the retina. ▶ The light rays striking the retina generate potentials in the rods and cones. ▶ Impulses initiated in the retina are conducted to the cerebral cortex, where they produce the sensation of vision.

13. Accommodation 38 ▶ I t is the process by which the curvature of lens is increased to see near object ▶ The problem of bringing diverging rays from close objects to a focus on the retina can be solved either by increasing the distance between the lens and the retina or by increasing the curvature or refractive power of the lens . ▶

14. A cc o mm o dati o n r ef l e x 39 The ability of the lens to adjust its shape to facilitate focusing. distant objects= thinner, less convex Close objects= lens thickens when one looks near object, the curvature of lens increases so the image of object falls on photoreceptors. parasympathetic stimulation to ciliary muscle ↑ convexity of lens ↑ refractive power accommodation for near vision Sympathetic stimulation to ciliary muscle ➢ ➢ ➢ ↓ curvature of lens ↓ refractive power Accommodation for far vision

15. Near Point Response 40 ▶ When the gaze is directed at a near object, the ciliary muscle contracts → relaxes the lens ligaments and lens become more convex shape. ▶ Accommodation is an active process, requiring muscular effort, and can therefore be tiring. ▶ The ciliary muscle is one of the most used muscles in the body. ▶ The degree to which the lens curvature can be increased is, of course limited, and light rays from an object very near the individual cannot be brought to a focus on the retina even with the greatest of effort. ▶ The nearest point to the eye at which an object can be brought into clear focus by accommodation is called the near point of vision .

16. 41 The Near Response In addition to accommodation, the visual axes converge and the pupil constricts when an individual looks at a near object. This three-part response—accommodation, convergence of the visual axes, and pupillary constriction—is called the near response. Mechanism of accommodation

17. T he Near Response cont’d.. ▶ The near point recedes throughout life, slowly at first and then rapidly with a d va n c i ng a g e. ▶ Lens become less elastic due to denature o f p r o tei n, w / c d e c rea s e a t w hi c h the curvature of the lens can be increased, r e s ul ti ng l o s s o f a c co mmo d a t i o n . ▶ By the time a normal individual reaches age 4 – 4 5 , t he l o s s o f a cc o mmo d a ti o n i s usually sufficient to make reading and close w o rk d i ffi cu l t. ( In a bi l i ty to f o c us ne a r objects) ▶ T hi s c o n d iti o n ( a g e r e l a ted p r o bl em) i s p r e s b y o p i a , c a n be c o r re c t e d by w e a r i ng g l a s s e s w i t h c o nv e x l e n s e s ( bi f o c a l l e n s) . 42

18. Cataracts ▶ O c c urs ma i nl y i n o l d pe o pl es ▶ Is the opacity of lens that reduces the transparent nature of lens. Causes ↑↑ glucose Tr a uma ( ra d i a ti o n) De g ener a t i o n a nd c o a g ul a ti o n o f l ens pr o tei ns w i th d ep o s iti o n o f ca - s a l t s Treatment : ▶ s ur g i ca l r em o v a l o f l ens 43

19. E rror s o f r e f r a c t i on ▶ Ref r a c t i v e err o r ( am et r o p i a ) i n w hi c h l i g ht r a y s c o m e t o a p o i n t f o c us e i t h er B e h i nd t he r et i n a ( hy p e r op i a ) o r In f r o nt o f r et i n a ( m yo p i a ) a nd Emmetropia (Normal Vision) Normal condition of the eyes; eyes with no refractive defects 48

20. My o pi a - n e a r s i g ht e dne ss it is result of too long axial length for refractive power of the eye. In this case the focal point is in front of retina. then distance objects can’t be focused on retina. The object can be seen clearly if it is moved closer to eye. ▶ Myopia is said to be genetic in origin. ▶ can be corrected with concave lens 49

21. when an axial length is too short for refractive power of the eye, then the distant objects can’t be focused clearly because the focal point is in back of retina. ▶ Sustained accommodation, even when viewing distant objects, can partially compensate for the defect, but the prolonged muscular effort is tiring and may cause headaches and blurring of vision. can be corrected with convex lens. Hypermetropia -farsightedness 50

22. In hyperopia , the eyeball is too short and light rays come to a focus behind the retina. A biconvex lens corrects this by adding to the refractive power of the lens of the eye. In myopia , the eyeball is too long and light rays focus in front of the retina. Placing a biconcave lens in front of the eye causes the light rays to diverge slightly before striking the eye, so that they are brought to a focus on the retina. Correction of Errors of refraction 51

23. Is tool of vision Site of image formation The retina is the light- sensitive portion of the eye that contains cones , which are responsible for color vision, and rods , which are mainly responsible for black and white vision and vision in the dark. R et i n a 52

24. Structural and Function Elements of the Retina Layers of the Retina are arranged in layers from the outside to the inside as follows: Pigmented layer Rods and cones layer Outer limiting layer Outer nuclear layer containing the cell bodies of the rods and cones Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglionic layer Optic nerve fibers layer Inner limiting membrane. Figure. Layers of retina. 53

25. ▶ 54 Retina consists of functional layers Pigmented layer cones and rods Bipolar cells Ganglion cell layer Amacrine cell layer Horizontal cell layer 1. Pigmented layer The receptor layer of the retina rests on the pigment epithelium next to the choroid. The pigment epithelium absorbs light rays , preventing the reflection of rays back through the retina. Such reflection would produce blurring of the visual images. Layers of the Retina cont’d…

26. Layers of the Retina cont’d… 2. cones and rods They are types of photoreceptors differ in : Shape Range of operation Distribution Visual function 55

27. Layers of the Retina cont’d… Cones & rods --- cont’d The outer segment of the cone is conical in shape. The rods are narrower and longer than the cones, but this is not always the case. Rods are 2-5 µm in diameter, Cones are 5-8 µm in diameter ▶ Ou te r p o rtion c o n tain photosensitive pigment ▶ I nn e r p i g m en t con c e r n e d with metabolic reaction 56

28. Cones & rods --- cont’d ▶ Ph ot op i g m e nt con s i s t s o f protein ( opsin ) & chromphore called retinine1 (aldehyde of vit.A) ▶ O ps i n pho t op i g m e nts consists Rod photopigment (rodopsin ) 3 cone photopigment 57

29. Function of cones & rods 59 I. C o lo r vis i on ▶ only cones involved in color vision II. Sensitivity to light ▶ Cones are sensitive to high light intensity Cones are responsible for day (photopic) vision ▶ III. visual acuity ▶ Cones have high level of visual acuity

30. CONES RODS 1. I n v o lv e d in c o l o r vi s i o n 1. Bl ack & wh i te vi s i o n 2. R e s p o n s ib l e fo r d ay ( ph o t o pic) l i ght 2. R e s p o n s ib l e f o r n ight (scotopic) light 3. Hi gh v i s ual acu i ty 3. L o w vi s u a l acuity 4. L o w e r i n numb e r 4. h i gh e r i n numb e r 5. C o nc. In f o v e a 5. Th ro ugh o ut in re tina but n o t i n f o v e a 6. C o ne s hap e d 6. R o d s h a p e d 7. Sh or t o ut e r s e g m e nt 7. L o ng e r o ut e r s e gm e nt 8. Synap s e w i th b i p o l a r c e l l s 1:1 8. Many to one Difference b/n rods & cones 60

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32. Visual acuity V i s u a l a c u i t y i s t he s p a t i a l r e s o l v i ng ca p a c i t y o f t h e vi su a l system. It i s t he a b i l i t y o f e y e s t o d i s t i n gu i s h bet w e e n t wo points. T h e m a x i m u m v i s u a l acu i t y i s i n t h e fo v e a c e ntra l i s . C l i n ic a l t e s t i s d a rk l e t te r o n l i gh t b ac k g r o u n d ( Sn e ll e n letter charts ) 62

33. R eti n a l l a y ers -- - c o n t’d Bipolar cells Transmit impulse from photoreceptors to ganglion cell layer Ganglion cell layer Are 2 nd order neurons Their axons made of optic nerve Amacrine cells Interconnect bipolar cells Horizontal cells Interconnect photoreceptors release inhibitory NTS NTS: Ach, GABA, DA, 5-HT, sub.p 63

34. Blind spot Blind spot The space where the ganglion cells leave the back of the retina is lacking P h o t o r e c ep t o r s . T h i s is the blind spot. Blind spot

35. Retinal detachment ▶ detachment of the rest of pigment epithelium t h e reti n a f rom t he can lead to hyperpolarization, however, attachment can be accomplished by laser surgery

36. ▪ The light-sensitive chemical in the rods is called rhodopsin The light-sensitive chemicals in the cones , called cone pigments or color pigments, have compositions only slightly different from that of rhodopsin. ▪ ▶ The outer segment of the rod has a concentration of light-sensitive pigment called rhodopsin , or visual purple , which is a combination of the protein scotopsin and the carotenoid pigment retinal (" retinene "). ▶ The retinal is a particular type called 11- cis retinal. This cis form of retinal is important because only this form can bind with scotopsin to synthesize rhodopsin. Photochemistry of Vision 67

37. Night Blindness ( nyctalopia ) 68 ▶ Night blindness occurs in any person with severe vitamin A deficiency. ▶ The simple reason for this is that without vitamin A, the amounts of retinal and rhodopsin that can be formed are severely depressed. ▶ This condition is called night blindness because the amount of light available at night is too little to permit adequate vision in vitamin A–deficient persons. ▶ For night blindness to occur, a person usually must remain on a vitamin A–deficient diet for months, because large quantities of vitamin A are normally stored in the liver and can be made available to the eyes. ▶ Once night blindness develops, it can sometimes be reversed in less than 1 hour by intravenous injection of vitamin A

38. Retinitis Pigmentosa ▶ Heter o g e neou s gr o u p o f here d i t a r y e ye disorders ▶ characterized by progressive vision loss ▶ du e t o a gr a d u a l d e gen er a t i on o f photoreceptors

39. Retinal adaptation 80 ▶ Is the ability of retina to adjust to d/t light intensities Dark Adaptation ▶ Is the mechanism of adjustment as one is transferred from light to dark. ▶ The following changes occur during the process of dark adaptation Pupillary dilation Formation of more photosensitive pigments ↑ in retinal sensitivity to light Visual acuity decrease The adjustment require half an hour Light Adaptation ▶ when a person come from a dark place into bright light, the eyes temporarily blind. Vision returns after a while. ▶ Light adaptation occur faster than dark adaptation (3-5min) ▶ Changes (reverse of dark adaptation) Pupillary constriction ↓ photosensitive pigments ↓ retinal sensitivity to light ▶ In dark, the eyes resynthesize the photopigments & become more sensitive to light. This is called dark adaptation .

40. Distribution of rods and cones ▶ De n s i t y o f r o d s m u c h g r e a t e r t h a n co n e s rods = 90million co n e s = 4 . 5 m i ll i o n Distribution: F o v e a : -cones only -one-to-one relationship with bipolar c e ll s a nd r e t i n a l ga n g l i o n c e l ls

41. ▶ Cones less sensitive than rods to light. ▶ Cones provide color vision and greater visual acuity. ▶ High light intensity bleaches out the rods, and color vision with high acuity is provided by cones. ▶ Trichromatic theory of color vision: ▶ According to the region of visual spectrum absorbed. - 3 types of cones: Erythrolable(red cones)- red sensitive(570nm) Chlorable(green cones)- green sensitive(535nm) Cyanoable(blue cones)- blue sensitive(445nm ) Cones and Co lor Vision

42. ▶ E ac h t y p e o f c o n e con tai ns retinene associated with photopsins. ▶ Photopsin protein is unique for each of the 3 cone pigment. The absorption characteristics of the pigments in the three types of cones show peak absorbencies at light wavelengths of 570, 535 and 445 nanometers for red, green & blue cones respectively. Cones and Color Vision (continued)

43. Color blindness 87 Color blind person fails to detect one or two colors, due to absence of particular type of cone photopigments . Color blindness is genetically inherited and seen more in males than in females. Color blindness is tested using Ishihara charts .

44. Color blindness 88 P a t i e nt s wi t h co l o r bli n dne s s c a n be c l a s s i fi ed i n t o : P r o t o n o pe s - l ac k r e d p i g m e n t D e u t e r a n o pe s - l ac k g r e e n pigment Tr i t a n o pe s - l ac k b l u e p i gm e n t M o n o c h r o ma t s - n o co n e p h o t o p i g m e n t un ab l e t o s ee an y co l o r g r een blue red

45. The visual field of one eye is that part of a sphere on which all objects seen by that eye when fixed on a point in a space Visual field is a conical space diverging distally from each eye. Vi s u a l F i e ld 89

46. 99 Light strikes retinal photoreceptors Photoreceptors stimulate 1 st order neuron (bipolar cells) Which stimulate 2 nd order neuron (ganglion cells) Optic nerves undergoes partial decussation at optic chiasma. The optic nerve fiber transmitting visual impulse from the nasal half of each retina cross opp. Side. Optic nerve tract fiber terminate in the following sites pretectal nucleus in MB sup. Colliculus in MB lateral geniculate body in thalamus Cells of LGB are 3 rd order neuron & they are called optic radiation . Their axon radiate through internal capsule to occipital lobe of c.cortex. area 17 - area 18 & 19 Summery of Neural pathway of vision

47. Effect of lesion in visual pathway 105 Right optic nerve lesion: ▶ Blindness of right eye ▶ Loss of direct pupillary light reflex Lesion in optic chiasma: ▶ Destruction of fibers from both nasal halves of retina ▶ Heteronymous hemianopia (half blindness of opp. Sides of visual fields) Lesion in optic tract: Blindness in half of visual field Bilateral lesion in area 18 & 19: Visual agnosia - the objects are seen in their form and color by means of area 17, but their nature, use, value can’t be perceived & the patient lose significance of written words ( visual aphasia )

48. Different eye disorder Iritis Inflammation of the iris ▶ White blood cells are shed into the anterior chamber of the eye in the aqueous humor. ▶ These cells can accumulate and cause adhesions between the iris and the lens. Treatments ▶ Antibiotics and steroids 106

49. Amblyopia ▶ Amblyopia is the medical term for poor development of vision in one eye. 107 ▶ [ambly- (dull) + -opia (vision)] ▶ Amblyopia is often referred to as "lazy eye." ▶ The eye is anatomically normal, but visual acuity is reduced even with glasses

50. Conjunctivitis I n f l a m m a t i o n o f t he co n j u n c t i va Cause Viruses Bacteria i rr i t a ti ng s ub s t a nc e s ( s ha m p o o , d i rt , s mo k e , po o l chlorine) s e xu a ll y t ran s m i tt e d d i s e a s e s (STDs) or allergens ( s ubs t an ce s t hat c au s e a l l e r g i e s ) c a n a l l c o n j unc t i v i t i s . 108

51. Exophthalmoses 109 ▶ Abnormal protrusion of the eyes ▶ Associated with hyperthyroidism and Grave’s disease. ▶ In the case of Graves Disease, the displacement of the eye is due to abnormal connective tissue deposition in the orbit and extraocular muscles ▶ If untreated, exophthalmos can causes the eye lids to fail to close during sleep leading to corneal damage. ▶ The process that it causing the displacement of the eye may also compress the optic nerve or ophthalmic artery leading to blindness

52. Blepharitis ▶ Inf l a mm a t i o n o f t h e e y e l i d m a r g i n s 110