OCULAR PHYSIOLOGY (I) Dr.Ahmed Al Shaibani Lab.2 Oct.2013 Objectives 1. Review of ocular anatomy (Ex. after image) 2. Visual pathway & field (Ex. Crossed & uncrossed diplopia, mechanical stimulation of the retina, blind spot localization, Light reflex & confrontation test ) 3. Visual acuity (Ex. Snellen chart) 4. Color vision (Ex. isheharaa test) 5. Fundoscopy (Ex. normal retinal appearance & structures) 6. Ocular motility & gaze position(ex. CN II,III,IV &VI exam ) Review of ocular anatomy Layers of the eye ball 1. Conjunctiva : is a transparent mucous membrane lining the inner surface of the eyelids and the surface of the globe as far as the limbus. It is richly vascular structure. 2. Cornea : is a complex structure which, as well as having a protective role, is responsible for about three quarters of the optical power of the eye. The normal cornea is free of blood vessels; nutrients are supplied and metabolic products removed mainly via the aqueous humour posteriorly and the tears anteriorly, with a downhill anterior posterior oxygen gradient. The cornea is the most densely innervated tissue in the body. 3. Sclera 4. Uveal tissue : is the vascular layer of the eye and comprises the iris, ciliary body and choroid. 5. retina
Anatomically,eye ball devided in to Ant. & post. Segment in relation to the lens; ant.segment include structures anterior to the lens (iris,cornea) while post.segment include structures posterior to lens (vitreous and retina) ). Anterior segment containn the ant. & post chamber( related to iris) Review of retina & photoreceptor Outer pigmented layer Neurosensory retina consists of photoreceptors, ganglion cells and interconnecting bipolar cells. Rod photoreceptors are responsible for night vision and detection of peripheral movement Cone photoreceptors are responsiblee for colour and central vision Ex.1// After image explain photoreceptor sensitivity and adaptation,light when stimulate photoreceptor will cause depletion of photosensitive pigment that lead to decrease photoreceptor sensitivity while photoreceptors exposed to darkness will keep themselvess highly sensitive (with low threshold to light),so when we close our eye after a period of concentration, the highly sensitive receptors will give light (brightness)illusions and vice versa. Visual pathway & field Retina devided in to 2 part; 1. Nasal retina that concernn with temporal field 2. Temporal retina that concern with nasal field
Optic nerve composed from nasal and temporal nerve fibers that represent the axons of nasal and temporal retinal ganglions respectively, nasal fibers are decussate at the optic chiasim to reach the contralateral temporal fiber forming the optic truct.fibers will synapss in the lateral geneculatee body and 2ndry fibers will travel through optic radiation to reach the visual cortex in the occipital lobe where the nerve impulses are processed to form the image. Exp II/Mechanical Stimulation of the Retina Explain that stimulation of nasal retina will give image in the temporal field and vice versa. Procedure Turn your gaze to the left, and shut both eyes. Keep looking to the left. With a fingertip, press gently on the right side of your right eyeball, at the corner of the eye. Note the visual effect. Slide your finger up and down, and note the direction of movement of the visual response. Turn your gaze to the right, and similarly press on the left side of your right eyeball, at the corner of the eye. Again, note the visual effect. You should find that the main visual response to stimulation is a bright circle or disc, on the opposite side of the visual field from the site of stimulation. Stimulation of the retina on the right side of the eye gives a response on the left, and vice versa.
Light reflex The pupil refers to the central opening in the iris. It acts as an aperture to improve the quality of the resulting image by controlling the amount of light that enters the eye. Pupillary light reflex: This reflex arc consists of an afferent path that detects and transmits the light stimuluss (through the optic nervee II) and an efferent path that supplies the muscles of the iris( through the oculomotor nerve III). Unilateral light stimulation will cause bilateral papillary reflex (why?) Pupil size ranges from approximately 1mm (miosis) to approximately 8mmm (mydriasis). Normally ideally 2.5 4mm. Pupils tend to be wider in teenagers and in darkness; joy, fear, or surprise due to increased sympathetic tone. Pupils tend to be narrower in the newborn due to parasympathetic tone, in light, during sleep, and in addicts Exp III/Testing the Light Reflex 1. Light reflex is tested in dim light where the pupil is slightly dilated. 2. The patient gazes into the distance to neutralize near field miosis. Direct and indirect light reflex: The examiner first covers both of the patient s eyes, then uncovers one eye or by projecting direct light to the examined eye. Normally the pupil will constrict after a latency period of about 0.2 seconds. Pupil reaction of the contralateral eye is called indirect or consensual light reflex.
Visual field VF is the area or space that is covered by vision.it is measured monocularly.normal limits extends approximately 50 superiorly, 60 nasally, 70 inferiorly and 90 temporally Assessment of VF by: 1. Confrontational method. 2. Perimetry method, which involves the presentation of a moving stimulus of known luminance or intensity from a non seeing area to a seeing area until it is perceived Pathologicall Interpretation 1. Depression 2. Field contraction 3. scotoma Indication 1. Screening 2. Follow up glaucoma 3. Visual pathway study Exp.IV//Procedure
1. Sit directly facing the patient, about 1 metre away 2. Your right eye infront his left eye. 3. Cover one eye for both of you. 4. Ask the patient to keep looking at your eyes. 5. Start to enter your finger or any target to the field. 6. Compare between your & patients field. 7. Repeat step 5 to remaining 3 field quarter. 8. Repeat the procedure for the other eye.