VISÃO MEIOS REFRATIVOS DO OLHO

Apresentação em tema: "VISÃO MEIOS REFRATIVOS DO OLHO"— Transcrição da apresentação:

1 VISÃO MEIOS REFRATIVOS DO OLHO
Dr. Nisreen Abo-elmaaty Physiology Department Dr. Nisreen Mansour

2 LUZ VISÍVEL A LUZ VISÍVEL (OU COMPRIMENTO DE ONDA ENTRE NM) SÓ PODE EXCITAR OS FOTORRECEPTORES OS RAIOS INFRA VERMELHOS NÃO PODEM EXCITAR, SÃO PERCEBIDOS APENAS COMO CALOR. OS RAIOS ULTRAVIOLETA SÃO FILTRADOS PELO CRISTALINO. Dr. Nisreen Mansour

3 CONCEITOS BÁSICOS REFRAÇÃO :
It is the bending of light rays when they travel in 2 transparent media with 2 different refractive indices, provided that they travel at angulated interface. INDICE DE REFRAÇÃO (IR) DE UM MEIO = velocidade da luz no ar velocidade da luz no meio e.x. O IR da cornea é 1.38 significa = velocidade da luz no ar / velocidade da luz na cornea = 1.38 Dr. Nisreen Mansour

4 Poder Refrativo = 1 metro / distância focal = ? Dioptrias.
Raios paralelos (vindos de > 6 m) alteram o seu curso nas bordas de uma lente convexa Num ponto determinado da lente, os raios passarão através de um ponto; Ponto Focal. Distância Focal : é a distancia entre o centro da lente e o Ponto Focal. PONTO FOCAL DISTÂNCIA FOCAL Poder Dioptrico da lente é a medida de sua capacidade de refratar os raios luminosos. Poder Refrativo = 1 metro / distância focal = ? Dioptrias. O Poder Dióptrico é inversamente relacionado com a Distância focal Dr. Nisreen Mansour

5 O GLOBO OCULAR 24 mm em diâmetro
3 camadas + fluidos intraoculares & câmaras Dr. Nisreen Mansour

6 CÂMARAS OCULARES & FLUIDOS
O CRISTALINO DIVIDE A CAVIDADE OCULAR EM 2 CÂMARAS PREENCHIDAS DE FLUIDOS INTRAOCULARES : CÂMARA ANTERIOR CÂMARA VITREA Anterior ao cristalino Dividida pela iris em: câmaras anterior & posterior. Preenchida com Humor Aquoso (fluido aquoso incolor) Posterior ao cristalino Preenchido com Humor Vitreo (fluido incolor gelatinoso) Dr. Nisreen Mansour

7 Clear transparent fluid filling ant. & post. chambers.
HUMOR AQUOSO Clear transparent fluid filling ant. & post. chambers. Formed by the epithelial lining of ciliary processes of ciliary body at a rate of 1-3 μl /min. Composition Relative to plasma, Aqueous H is: - alkaline, nearly protein-free fluid - Higher Na+ & HCO3 content - Higher vit. C, pyruvic & lactic acids - Lower glucose Dr. Nisreen Mansour

8 CIRCULAÇÃO & DRENAGEM DO HUMOR AQUOSO
cristalino H. Aquoso sai dos processessos ciliares→ flui entre os ligamentos suspensores→ câmara posterior → através da pupila→ Câmara ant. → através do ângulo iridocorneal (angulo de filtração) →espaço de Fontana → canal de Schlemm → veias aquosas → veias episclerais → veias sistêmicas Dr. Nisreen Mansour

9 FUNÇÕES DO HUMOR AQUOSO
One of refractory media of the eye Supply of O2 & nutrients for avascular cornea & lens. Buffering & removal of acid products of anaerobic metabolism of cornea & lens. Keeping intraocular pressure (IOP) constant by the balance between its formation & drainage. Dr. Nisreen Mansour

10 HUMOR VITREO Transparent gelatinous mass held together by fibrillar network. (little flow of fluid; Vitreous body). Filling the space between lens & retina. Separated from lens by a very narrow Retrolental space. Enclosed in a thin hyaloid membrane, firmly adherent to retina around optic disc. Functions: - one of the refractive media of the eye. - support of intracocular structures (lens & retina). - Maintenance of spherical shape of eye. Dr. Nisreen Mansour

11 MEIOS REFRATIVOS DO OLHO
INDICE DE REFRAÇÃO (IR) PODER REFRATIVO Ar 1 Cornea 1.38 +39 Dioptrias Humor Aquoso 1.33 Cristalino 1.40 +20 Dioptrias Humor Vítreo 1.34 The refractive power of cornea is mainly due to its anterior The Lens: half of bending occurs at its ant. surface & half at its posterior surface. Dr. Nisreen Mansour

12 O SISTEMA ÓPTICO DO OLHO
The divergent light rays must pass through an optical system that brings them back into focus. The cornea & lens is the optical system of the eye that focus light rays onto the retina Dr. Nisreen Mansour

13 CORNEA It is the transparent anterior 1/6 of outer layer.
Its thickness is 1mm at the periphery & 0.5 mm at centre. Richly supplied by sensory nerve endings (branches of ophthalmic division of V cranial n). The cornea itself is avascular, but the corneoscleral junction is richly supplied by capillaries. Derives its nutrition from aqueous humour (glucose), tear film (O2) & corneoscleral capillaries. Dr. Nisreen Mansour

14 FUNÇÕES DA CÓRNEA 1- The most powerful refractive medium of eye; 39 dioptres (2/3 of refractive power of eye) → formation of sharp clear image. 2- Protective for sensitive intraocular structures: - tough. - absorbs UV rays. - initiator of Corneal reflex which is a protective reflex. Dr. Nisreen Mansour

15 Non-myelinated nerve fibres running parallel to collagen fibres.
O QUE CAUSA A TRANSPARÊNCIA CORNEANA ? 1- ESTRUTURA ANATÔMICA Non-vascularity Regular arrangement of collagen fibres of substantia propria & of corneal epithelium. Non-myelinated nerve fibres running parallel to collagen fibres. 2- DETURGÊNCIA CORNEANA Achieved by an active endothelial pump → maintenance of corneal fibres packed together. Dr. Nisreen Mansour

16 ANORMALIDADES DA CÓRNEA
1. OPACIFICAÇÃO CORNEANA ; - is partial loss of corneal transparency. - is a complication of corneal ulcer. - ttt: corneal grafting. 2. ASTIGMATISMO; - the corneal curvature is not equal in all planes. - ttt: cylinderical or contact lens. 3. CERATOCONE (CORNEA CÔNICA ); - congenital condition characterised by conical protrusion of cornea. - usually bilateral & appears at puberty. - ttt: contact lens or corneal grafting. Dr. Nisreen Mansour

17 O CRISTALINO Is a biconvex lens composed of a strong elastic capsule filled with viscous transparent proteinaceous fluid. Lens diameter ~ 10 mm, its thickness ~ 4 mm. The capsule is attached to ciliary body by suspensory ligaments (70), the tension of these ligaments is controlled by ciliary ms. Dr. Nisreen Mansour

18 The Lens Its transparency is caused by
uniform arrangement of its fibres, no blood vessels, dehydration normal lens metabolism. Is avascular; derives its nutrition & O2 supply from aqueous humour. Dr. Nisreen Mansour

19 Dr. Nisreen Mansour

20 FUNÇÃO DO CRISTALINO The 2nd major refractive medium of the eye; Its refractive power (20 dioptres) represents ~ 30% of total refractive power of the eye. The important is that the lens is the only player responsible for adjustment for distance; It can increase its refractive power, in response to nerve signals from the brain, providing the important mechanism of Accommodation. Dr. Nisreen Mansour

21 REFLEX O DE ACOMODAÇÃO (RESPOSTA DE PERTO)
Accommodation is the ability of the eye to keep the image of an object focused on the retina as the distance between the object & retina varies Accommodation Reflex (Near Response) is the changes occurring in the eye as a result of retinal blurred image of the near object. Response: 1- Constriction of the pupils. 2- ↑ Thickness of the lens (more spherical; becomes very convex (instead of moderate convexity). 3- Medial convergence of the eyes. Dr. Nisreen Mansour

22 Dr. Nisreen Mansour

23 The lens becomes more spherical during near vision (contraction of ciliary muscle)
Dr. Nisreen Mansour

24 VIA DO REFLEXO DE ACOMODAÇÃO :
Blurred retinal image → retinal nervous elements → optic nerve → optic chiasma → optic tract →LGB (thalamus) → optic radiation → primary visual area; 17; occipital lobe & association visual area; 18, 19 Area 8, Frontal eye field area Superior Colliculus, midbrain Somatic III n. supplying medial recti Edinger-Westphall n. of III n. Convergence Ciliary ganglion The image falls on fovea centralis + Ciliary ms. +Constrictor pupillae ms. ↑ curvature of lens ↑ its refractive power ↑ depth of focus ↓ excess light Prevents aberrations Dr. Nisreen Mansour

25 VIA REFLEXA DA ACOMODAÇÃO
Dr. Nisreen Mansour

26 AMPLITUDE DE ACOMODAÇÃO
Is the difference between refractive power of the lens on maximum accommodation & in far vision when the lens is fully relaxed. It decreases gradually with age due to loss of lens elasticity & weakness of ciliary ms. PONTO PRÓXIMO The nearest point is the minimal distance from the eye at which an object can be brought into focus recedes with age (same reasons above). Dr. Nisreen Mansour

27 Amplitude of Accommodation
Age (years) Nearest point (cm) Amplitude of Accommodation (dioptres) 10 14 20 30 7 40 50 5 60 100 1 Dr. Nisreen Mansour

28 Corrected by wearing convex lens for near vision (e.g. reading).
PRESBIOPIA is the physiological progressive loss of the accommodation with age due to loss of elasticity of the lens (partly because of denaturation of lens proteins), until the lens becomes totally non-accommodating at the age of 70 years. Corrected by wearing convex lens for near vision (e.g. reading). Dr. Nisreen Mansour

29 If this does not occur → an error of refraction
VÍCIOS DE REFRAÇÃO In normal eye (emmetropic), parallel rays from distant objects converge to a focus on the retina, provided that the ciliary ms. is completely relaxed. If this does not occur → an error of refraction Hipermetropia (olho curto). Miopia (olho longo). Astigmatismo. Dr. Nisreen Mansour

30 MIOPIA (OLHO LONGO) Dr. Nisreen Mansour

31 HIPERMETROPIA (OLHO CURTO)
Dr. Nisreen Mansour

32 VÍCIOS DE REFRAÇÃO NORMAL - EMÉTROPE MIOPIA HIPERMETROPIA
MIOPIA CORRIGIDA HIPERMETROPIA HIPERMETROPIA CORRIGIDA Dr. Nisreen Mansour

33 Myopia Hypermetropia Astigmatism
Defect Focus in front of retina Focus behind retina Focus of rays in one plane is at different distance from that of rays in another plane. Cause -long eye ball -Strong lens -short eye ball - Weak lens - Unequal curvature of cornea or lens. ttt Biconcave lens (diverge) Biconvex lens (↑refractive power) Cylindrical lens in suitable plane Contact lens. Dr. Nisreen Mansour

34 During near vision, which of the following is false?
The tension in the suspensory ligaments is increased The tension in the lens capsule is decreased The lens becomes more round There is an increased signal to ciliary muscle Dr. Nisreen Mansour

35 Dr. Nisreen Mansour

36 CONTROLE DO DIÂMETRO PUPILAR
The diameter of the pupil varies between 1.5 mm (bright light) – 8 mm (darkness). This achieved by the presence of 2 smooth muscles; 1-Constrictor pupillae ms.; its fibres arranged in a circular manner around pupil. Receives motor postgang.para-sympathetic supply along short Ciliary nerves (pregang.from EW n of III relay in ciliary ganglion). 2- Dilator pupillae ms.; its fibres arranged radially around pupil. Receives post gang. sympathetic from SCG (pregang. arise in 1, 2 Thoracic segments. Dr. Nisreen Mansour

37 CONTROL E DO DIÂMETRO PUPILAR
The diameter of the pupil varies between 1.5 mm (bright light) – 8 mm (darkness). This achieved by the presence of 2 smooth muscles; 1-Constrictor pupillae ms.; its fibres arranged in a circular manner around pupil. Receives motor postgang.para-sympathetic supply along short Ciliary nerves (pregang.from EW n of III relay in ciliary ganglion). 2- Dilator pupillae ms.; its fibres arranged radially around pupil. Receives post gang. sympathetic from SCG (pregang. arise in 1, 2 Thoracic segments. Dr. Nisreen Mansour

38 Dr. Nisreen Mansour

39 REFLEXO A LUZ Stimulus: exposure of one eye to light.
Response: Ipsilateral constriction of pupil (Direct Light Reflex) & Contralateral pupillary constriction (Indirect or consensual Light Reflex). Pathway: light → retinal nervous elements → optic nerve →optic chiasma → optic tract → ipsilateral pretectal nucleus in midbrain → along tectonuclear tract around aqueduct of Sylvius → to EW nuclei (parasymp n of III) of both sides → motor pregang. to ciliary ganglion → post ganglionic along short ciliary nerves → + bilateral constrictor pupillae ms. → bilateral constriction of pupils. Dr. Nisreen Mansour

40 LUZ MESENCÉFALO REFLEXO A LUZ Dr. Nisreen Mansour

41 PUPILA DE ARGYLL-ROBERTSON NÃO-REATIVA À LUZ MAS REATIVA À ACOMODAÇÃO.
DEVIDO A LESÃO DO TRACTO TECTONUCLEAR (POR SIFILIS OU SIRINGOMIELIA DO AQUEDUTO DE SILVIO). PUPILA REVERSA ARGYLL-ROBERTSON NÃO-REATIVA A ACCOMODAÇÃO MAS REATIVA À LUZ. DEVIDO A LESÃO NO TRACTO OCCIPITOTECTAL. Dr. Nisreen Mansour

42 O CAMPO VISUAL CAMPO BINOCULAR CAMPO D CAMPO E Dr. Nisreen Mansour

43 VIAS ÓPTICAS E DEFEITOS DE CAMPO
CEGUEIRA DO OLHO IPSILATERAL ANOPIA DE O.E. b→ HEMIANOPIA BITEMPORAL HEMIANOPIA HETERÔNIMA C → HEMIANOPIA HOMÔNIMA LESÃO DA AREA 17 (D) → HEMIANOPIA HOMÔNIMA DO LADO OPOSTO COM LIVRAMENTO MACULAR Dr. Nisreen Mansour

44 BOA SORTE Dr. Nisreen Mansour