Dr. Nisreen Mansour

VISÃOMEIOS REFRATIVOS DO OLHO

Dr. Nisreen Abo-elmaatyPhysiology Department

Dr. Nisreen Mansour

LUZ VISÍVEL

• A LUZ VISÍVEL (OU COMPRIMENTO DE ONDA ENTRE 400-700 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

CONCEITOS BÁSICOSREFRAÇÃO :• 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

PONTO FOCAL

DISTÂNCIA FOCAL

• 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.

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

O GLOBO OCULAR

• 24 mm em diâmetro• 3 camadas + fluidos intraoculares & câmaras

Dr. Nisreen Mansour

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

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

CIRCULAÇÃO CIRCULAÇÃO & DRENAGEM DO HUMOR AQUOSO

H. Aquoso sai dos processessos ciliares→ flui entre os ligamentos H. Aquoso sai dos processessos ciliares→ flui entre os ligamentos suspensores→ câmara posterior → através da pupila→ Câmara suspensores→ câmara posterior → através da pupila→ Câmara ant. → através do ângulo iridocorneal (angulo de filtração) ant. → através do ângulo iridocorneal (angulo de filtração) →espaço de Fontana → canal de Schlemm → veias aquosas → →espaço de Fontana → canal de Schlemm → veias aquosas → veias episclerais → veias sistêmicasveias episclerais → veias sistêmicas

cristalino

Dr. Nisreen Mansour

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

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

MEIO INDICE DEREFRAÇÃO

(IR)

PODERREFRATIVO

Ar 1

Cornea 1.38 +39 DioptriasHumor Aquoso 1.33Cristalino 1.40 +20 DioptriasHumor 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.

MEIOS REFRATIVOS DO OLHO

Dr. Nisreen Mansour

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

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

FUNÇÕES DA CÓRNEA1- 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

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 CORNEANAAchieved by an active endothelial pump → maintenance

of corneal fibres packed together.

Dr. Nisreen Mansour

ANORMALIDADES DA CÓRNEA1. 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

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.

O CRISTALINOO CRISTALINO

Dr. Nisreen Mansour

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

Dr. Nisreen Mansour

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

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

Dr. Nisreen Mansour

The lens becomes more spherical The lens becomes more spherical during near vision (contraction of during near vision (contraction of

ciliary muscle)ciliary muscle)

Dr. Nisreen Mansour

• 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

Convergence

Edinger-Westphall n. of III n.

Ciliary ganglion

+ Ciliary ms. +Constrictor pupillae ms.The image falls on fovea centralis

↑ curvature of lens↑ its refractive power

↑ depth of focus↓ excess lightPrevents aberrations

Dr. Nisreen Mansour

VIA REFLEXA DA ACOMODAÇÃO

Dr. Nisreen Mansour

• 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

Age

(years)

Nearest point

(cm)

Amplitude of Accommodatio

n(dioptres)

10 10 14

20 14 10

30 20 7

40 50 5

60 100 1

Dr. Nisreen Mansour

PRESBIOPIAPRESBIOPIA is the physiological progressive is the physiological progressive

loss of the accommodation with loss of the accommodation with age due to loss of elasticity of the age due to loss of elasticity of the lens (partly because of lens (partly because of denaturation of lens proteins), denaturation of lens proteins), until the lens becomes totally non-until the lens becomes totally non-accommodating at the age of 70 accommodating at the age of 70 years.years.

Corrected by wearing convex lens Corrected by wearing convex lens for near vision (e.g. reading).for near vision (e.g. reading).

Dr. Nisreen Mansour

• 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

• VÍCIOS DE REFRAÇÃO 1. Hipermetropia (olho curto).2. Miopia (olho longo).3. Astigmatismo.

Dr. Nisreen Mansour

MIOPIA (OLHO LONGO)

Dr. Nisreen Mansour

HIPERMETROPIA (OLHO CURTO)

Dr. Nisreen Mansour

VÍCIOS DE REFRAÇÃOVÍCIOS DE REFRAÇÃO

MIOPIA

MIOPIA CORRIGIDA

NORMAL - EMÉTROPE

HIPERMETROPIA

HIPERMETROPIA CORRIGIDA

Dr. Nisreen Mansour

Myopia Hypermetropia Astigmatism

DefecDefectt

Focus in Focus in front of retinafront of retina

Focus behind Focus behind retinaretina

Focus of rays in Focus of rays in one plane is at one plane is at different different distance from distance from that of rays in that of rays in another plane.another plane.

CauseCause -long eye ball-long eye ball-Strong lens-Strong lens

-short eye ball-short eye ball- Weak lens- Weak lens

- Unequal - Unequal curvature of curvature of cornea or lens.cornea or lens.

tttttt Biconcave Biconcave lens (diverge)lens (diverge)

Biconvex lens Biconvex lens ((↑↑refractive refractive power)power)

Cylindrical lens Cylindrical lens in suitable planein suitable planeContact lens.Contact lens.

Dr. Nisreen Mansour

• During near vision, which of the following is false?

a) The tension in the suspensory ligaments is increased

b) The tension in the lens capsule is decreasedc) The lens becomes more roundd) There is an increased signal to ciliary

muscle

Dr. Nisreen Mansour

Dr. Nisreen Mansour

CONTROLE DO DIÂMETRO PUPILARCONTROLE 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

CONTROL E DO DIÂMETRO PUPILARThe 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

Dr. Nisreen Mansour

REFLEXO A LUZREFLEXO A LUZ StimulusStimulus: exposure of one eye to light.: exposure of one eye to light. ResponseResponse: Ipsilateral constriction of pupil (: Ipsilateral constriction of pupil (Direct Direct

Light Reflex)Light Reflex) & Contralateral pupillary constriction & Contralateral pupillary constriction ((Indirect or consensual Light ReflexIndirect or consensual Light Reflex).).

PathwayPathway: light : light →→ retinal nervous elements retinal nervous elements →→ optic optic nerve nerve →→optic chiasma optic chiasma →→ optic tract optic tract →→ ipsilateral ipsilateral pretectal nucleus in midbrainpretectal nucleus in midbrain →→ along tectonuclear along tectonuclear tract around tract around aqueduct of Sylviusaqueduct of Sylvius →→ to to EW nuclei EW nuclei (parasymp n of III) of both sides(parasymp n of III) of both sides →→ motor pregang. motor pregang. to ciliary ganglion to ciliary ganglion →→ post ganglionic along short post ganglionic along short ciliary nerves ciliary nerves →→ + bilateral constrictor pupillae ms. + bilateral constrictor pupillae ms. →→ bilateral constriction of pupils. bilateral constriction of pupils.

Dr. Nisreen Mansour

REFLEXO A LUZMESENCÉFALO

LUZ

Dr. Nisreen Mansour

PUPILA DE ARGYLL-ROBERTSON NÃO-REATIVA À LUZ MAS REATIVA À NÃO-REATIVA À LUZ MAS REATIVA À

ACOMODAÇÃO.ACOMODAÇÃO. DEVIDO A LESÃO DO TRACTO TECTONUCLEAR DEVIDO A LESÃO DO TRACTO TECTONUCLEAR

(POR SIFILIS OU SIRINGOMIELIA DO AQUEDUTO (POR SIFILIS OU SIRINGOMIELIA DO AQUEDUTO DE SILVIO).DE SILVIO).

PUPILA REVERSA ARGYLL-ROBERTSONPUPILA REVERSA ARGYLL-ROBERTSON NÃO-REATIVA A ACCOMODAÇÃO MAS REATIVA À NÃO-REATIVA A ACCOMODAÇÃO MAS REATIVA À

LUZ.LUZ. DEVIDO A LESÃO NO TRACTO OCCIPITOTECTAL. DEVIDO A LESÃO NO TRACTO OCCIPITOTECTAL.

Dr. Nisreen Mansour

O CAMPO VISUALO CAMPO VISUALCAMPO BINOCULAR

CAMPO E CAMPO D

Dr. Nisreen Mansour

a. CEGUEIRA DO OLHO IPSILATERAL

ANOPIA DE O.E.

b→ HEMIANOPIA BITEMPORALHEMIANOPIA HETERÔNIMA

C → HEMIANOPIA HOMÔNIMA

LESÃO DA AREA 17 (D) → HEMIANOPIA HOMÔNIMADO LADO OPOSTO COM LIVRAMENTO MACULAR

VIAS ÓPTICAS E DEFEITOS DE CAMPO

Dr. Nisreen MansourDr. Nisreen Mansour

BOA SORTEBOA SORTE