Faal Penglihatan (2) PDF

 Learning Objectives  Describe the light reflex  Describe production of nerve impulses in the eyes & trace the visual pathways to their destinations in the brain.  Define and explain dark adaptation  Explain how we are able to distinguish colors.  Explain how we are a...

 Learning Objectives  Describe the light reflex  Describe production of nerve impulses in the eyes & trace the visual pathways to their destinations in the brain.  Define and explain dark adaptation  Explain how we are able to distinguish colors.  Explain how we are able to perceive depth.  Describe the eye movement Nurfitri Bustamam 2  Refleks Pupil Nurfitri Bustamam 3  Refleks Pupil  Pupil konstriksi utk mengurangi sinar yg masuk, pupil sebelahnya ikut konstriksi (consensual light reflex).  Jalur reflex pupil berbeda dg akomodasi  Pupil Argyll-Robertson: akomodasi intact tetapi refleks pupil hilang sebab adanya lesi di midbrain (misalnya syphilis)  Lengkung refleks: n opticus brachium of the superior colliculus pretectal nucleus ipsilateral & contralateral Edinger-Westphal nucleus ciliary ganglion (N. III) sphincter pupilae (otot sirkularis). Nurfitri Bustamam 4  Lengkung Refleks Pupil Nurfitri Bustamam 5  Phototransduction in rods & cones Structural changes in the Incident light retinene of photopigment Metarhodopsin II Activation of transducin  Semakin kuat cahaya semakin besar respons Activation of photodiesterase hiperpolarisasi  Neurotransmiter yg Decreased intracelular cGMP dihasilkan fotoreseptor bersifat inhibisi Closure of Na+ channels Hyperpolarization Decreased released of Response in bipolar cells synaptic transmitter & other neural elements Nurfitri Bustamam 6 Nurfitri Bustamam 7 Nurfitri Bustamam 8 Nurfitri Bustamam 9 Nurfitri Bustamam 10 Nurfitri Bustamam 11  Kemampuan mata beradaptasi terhadap cahaya sangat tinggi (10-7 – 107 mm Lambert) krn ada 2 fotoreseptor & ada pengaturan pupil  Rod vision (scotopic vision)  Transition zone  Cone vision: rhodopsin terurai  Rod vision: rhodopsin terbentuk & dirombak seperlunya  Diperlukan waktu utk menumpuk rhodopsin yg terurai saat terang Nurfitri Bustamam 12  Semakin byk rhodopsin, fotoreseptor semakin sensitif terhadap cahaya. Nurfitri Bustamam 13 Nurfitri Bustamam 14  Buta senja (Nyctalopia) Pada defisiensi vit. A, pembentukan rhodopsin lambat. Mengapa disebut buta senja? Bagaimana perubahan intensitas cahaya pada senja hari? Nurfitri Bustamam 15  Adaptasi Gelap & Adaptasi Terang  Adaptasi Gelap  Perub. terang ke gelap: retina “buta”, perlahan mampu/terbiasa melihat dlm gelap. Penurunan ambang visual “adaptasi gelap” yg lamanya 20-30 menit. Terdapat 2 komponen adaptasi gelap:  Adaptasi gelap cones: cepat, sdkt/kecil, hanya di daerah fovea & sekitarnya.  Adaptasi gelap rods: lambat, lbh besar, lbh lama, utk daerah perifer retina. Nurfitri Bustamam 16  Kacamata merah akan memperpendek masa adaptasi gelap karena gelombang sinar merah hanya sedikit merangsang rods, tetapi cones tetap mampu berfungsi seperti biasa (studio foto/kamar gelap, radiologist, pilot terbang malam)  Masa adaptasi gelap adalah masa pembentukan rhodopsin (jika kena sinar rusak). Diperlukan jumlah rhodopsin cukup utk mampu melihat dalam gelap.  Dari gelap ke terang: silau, cahaya terlalu terang, tetapi lama kelamaan terbiasa dalam terang, adaptasi cahaya (light adaptation) lamanya  5 menit. Nurfitri Bustamam 17  An object can absorb certain wavelengths of visible light and reflect others; the object will appear the color of the wavelength that is reflected. Nurfitri Bustamam 18  Garden by the Bay, Singapore Nurfitri Bustamam 19  Melihat Warna  Teori YOUNG HELMHOLTZ: manusia mempunyai 3 cones  Sensasi warna ditentukan oleh frekuensi relatif & impuls dari tiap jenis kerucut.  Ke-3 sel kerucut dapat terangsang dg intensitas yg berbeda atau hanya 1 jenis kerucut yg terangsang sehingga dapat melihat berbagai kombinasi warna.  MEJIKUHIBINIU (ROY G BIV) Nurfitri Bustamam 20  Colorblindness (buta warna)  Test: Ishihara charts  Buta warna: tdk dpt membedakan warna tertentu.  Anomaly: thd warna tertentu lemah, tdk cerah  Anopia: buta warna, protanopia (buta warna merah), deuteranopia (buta warna hijau), trianaopia (buta warna biru).  Trichromat (punya 3 cones), dichromat (2 cones), monochromat (hanya punya 1 macam cones) Nurfitri Bustamam 21 Nurfitri Bustamam 22  Visual Pathway Stimulus (ligth) Rods & Cones Retina Bipolar Cells Gangglion Cells Optic nerve Thalamus Lateral Geniculate Nucleus Pathway Visual Cortex Cortex Visual Association Cortex Nurfitri Bustamam 23 Nurfitri Bustamam 24 Nurfitri Bustamam 25  Pusat Penglihatan Nurfitri Bustamam 26  Visual Fields  The technique of perimetry allows precise mapping out visual fields  The visual fields are determined by the position of the orbits, the extent and shape of the retina in each eye and the external obstruction to the incidence of light (nose & brow). Nurfitri Bustamam 27 Nurfitri Bustamam 28   Proyeksi lapang pandang dapat digunakan utk menentukan lokasi kerusakan di jaras penglihatan Nurfitri Bustamam 29  Ada berapa ekor binatang yang anda lihat? Nurfitri Bustamam 30 Nurfitri Bustamam 31  Monocular & Binocular Vision Nurfitri Bustamam 32 Penglihatan binokular  Melihat dg kedua mata dan memfokuskan dua bayangan yang diterima masing-masing mata menjadi satu fusi bayangan.  Memungkinkan menentukan kedalaman benda yang dilihat (tiga dimensi) secara akurat, kanan maupun kiri (stereoskopik)  Depth Perception  If you close your right eye then open it and close your left, you will notice that the picture changes somewhat.  Each eye receives a slightly different image, because their foveas are 2-3 inches apart. For one thing, each eye provides some visual information that is unavailable to the other because your nose and eye socket block its view of the opposite side.  Each eye sees the world from a slightly different angle. The association & integrative areas of the cortex compare these views and use them to provide us with depth perception. Nurfitri Bustamam 34 Nurfitri Bustamam 35  Stereoscopic Vision Nurfitri Bustamam 36 Nurfitri Bustamam 37  Depth Perception Test Nurfitri Bustamam 38  Gambar apakah yang Anda lihat? Nurfitri Bustamam 39  Otot-otot bola mata Nurfitri Bustamam 40  Eye Movements 1. Saccades movement: melihat dg cepat & meloncat-loncat 2. Smooth persuit movement: mengikuti gerak objek 3. Convergence movement 4. Vestibular movement Nurfitri Bustamam 42  Eye Movement Disorders  Strabismus: uncoordinated extrinsic eye muscles, primary symptom: diplopia Diplopia (double vision), results when the contraction of the extrinsic muscles is not coordinated. The eyes focus on different area of the visual field & two images are seen.  Nystagmus: involuntary unilateral or bilateral rhytmic movement of the eyes.  Paralysis of extraocular muscle: ptosis: dropping of the eyelid Nurfitri Bustamam 43 Nurfitri Bustamam 44