4 Vision I

• Eyeball


  A hollow, fluid space
• Coats of the Eyeball


  • Fibrous/Outer Layer
  • Vascular/Muscular/Middle Layer
  • Nervous/Inner Layer
• Sclera


  • White of the eye
  • Anteroposterior 5/6 of the fibrous layer
  • Dense irregular collagenous tissue
  • Firm, white outer connective tissue layer
  • Helps maintain the shape of the eye
  • Protects the internal structures
  • Provides attachment for intrinsic eye muscles
• Cornea


  • Anterior 1/6 of the fibrous layer
  • Dense regular collagenous tissue
  • Transparent layer that permits light to enter the eye
  • Bends or refract the entering light
  • Most powerful and major refractive medium of the eye
• Choroid


  • Posterior portion
  • Contains most of the blood vessel
  • Has pigment epithelium so that the light rays that will pass the lens and pupil will not go through and through; and will just bend
  • Melanin-containing pigment cells
  • Provides nutrients to all eye layers
  • Black color absorbs light preventing reflecting and scattering of light within the eye
• Ciliary Body


  • Middle portion
  • Contains smooth muscles (ciliary muscles) which attach to the perimeter of the lens by suspensory ligament (Zonular ligaments)
  • Suspensory ligaments holds lens in place
  • Ciliary muscles (smooth muscles) pull on the ligaments to change the thickness of the lens
  • When they contract, they contract towards the suspensory ligaments
  • When they relax, they relax towards the periphery
  • Lens pulled in: power is decreased
  • Lens allowed to bulged (rounder): power is increased
  • Ciliary processes secrete aqueous humor
• Iris


  • Anterior portion
  • Colored part of the eyes
  • Has pigment epithelium at its most posterior aspect which gives color to the eye which contains: Melanin: produces brown color, Pheomelanin: produces other colors
  • Anterior chamber: at the front of the iris
  • Posterior chamber: at the back of the iris
  • Involved in the regulation of entry of light into the retina
  • Increasing depth of focus by constriction
  • Limits passage of light to central parts of lens forming clear image on the retina
  • Diagnosis of disease affecting reflexes of the pupil
• Parasympathetic (CN III)


  • Circular muscles contract
  • Pupillary constriction
• Sympathetic


  • Radial muscles contract
  • Pupillary dilation
• Retina


  • Does not entirely cover the eye
  • Forms retinal images; while the object is seen in the visual field
  • Axis of the light rays (180°) goes toward the depression (macula lutea)
  • Inside the macula lutea is the fovea centralis
• Corneoscleral junction


  • Junction between the sclera and the cornea
  • Where the canal of Schlemm is located
• Canal of Schlemm


  • Where the aqueous humor produced by the ciliary processes is drained
  • If the aqueous humor is not drained, it will accumulate in the anterior chamber, which increases the intra-ocular pressure and compresses some eye structures including the retina, leading to glaucoma
  • Closed-angle Glaucoma: when there is obstruction in the Canal of Schlemm
  • Open-angle Glaucoma: no obstruction but the ciliary processes has excessive production of aqueous humor
• Conjunctiva


  • Located in front of the cornea
  • Should be conjunctival reflex (not corneal reflex) because the cornea does not contain receptors
• Ora Serrata


  Anterior termination of the retina
• Pupil


  • Just a space in the eyeball
  • Black in color because there is no light inside the eyes
  • Ophthalmoscope: provides light inside the eyes to see what is inside
• Lens


  • Biconvex
  • Distributes light rays
  • Must form a focal point towards the macula which contains fovea centralis
• Fovea centralis


  • Most acute vision
  • Clearest vision
  • 1:1:1 ratio: 1 photoreceptor (cone) is connected to 1 bipolar cell which is connected to 1 ganglion cell
  • This ratio makes the image very accurate
  • Only made up of cones
  • Cones in this area are very slender
• Optic Disk


  • Aka optic papilla
  • Blind spot
  • Has no photoreceptors
  • Has axons of ganglion cells that form the optic nerve (CN II)
• Vitreous Canal


  • Contains vitreous humor
  • Transmits light within the posterior segment
  • Supports the lens posteriorly
  • Holds the retina in place
  • Contributes to intra-ocular pressure (10-22 mmHg)
  • Gives mostly the entire shape of the eyeball
  • The bulk of the eyes is formed by the vitreous humor present in the vitreous canal
• Floaters


  Can sometimes be seen especially when one is frequently dehydrated or old (atrophy of the vitreous canal)
• Intervention: ophthalmoscopy, hydration then refer to Ophthalmologist
• Iris


  • Governs the constriction and dilation of the eyes
  • CONSTRICTION= contraction of circular muscle/constrictor pupillae
  • DILATION= contraction of the radial muscle/ dilator pupillae
• Normal Pupil Size


  • 1.5mm (constricted)
  • 10mm (very dilated; common in dead people and those that use stimulants)
• Flow of the Aqueous Humor

  From the ciliary process -> posterior chamber -> pupil -> anterior chamber -> canal of Schlemm (in corneoscleral/ iridocorneal junction)
• Zonular/Suspensory Ligaments


  • Hold the lens in place
  • In cataract extraction: extraction of the cataract followed by lens replacement, the lens will lose its ability to reduce/increase power because it is not suspended to the ligaments anymore, eyeglasses are needed to replace the ligaments' action for near vision
• Crystalline Lens


  • Usually held up by the suspensory ligaments
  • Bend the incoming light rays
• Focal Point


  • Point at which all of the light rays will converge in the eye
  • Should fall in the retina- in the fovea centralis of the macula lutea so one could see the object clearly
• Nearsightedness/ Myopia


  • Focal point falls before the retina
  • Leans forward to see/read
  • Eyeball is long and lens is too strong
  • BICONCAVE LENS (spherical) to correct
• Farsightedness/ Hyperopia


  • Focal point falls after the retina
  • Leans away to see/read
  • Eyeball is too short and lens is weak
  • BICONVEX LENS (spherical) to correct
• Even if the lens is normal but the eyeball is LONG, the focal point falls before the retina causing MYOPIA, or the eyeball is shorter than normal, focal point falls behind the retina causing HYPEROPIA
• Crystalline Lens


  • Usually held up by the suspensory ligaments
  • Bends the incoming light rays
• Focal Point


  • Point at which all of the light rays will converge in the eye
  • Should fall in the retina- in the fovea centralis of the macula lutea so one could see the object clearly
• Nearsightedness/Myopia


  • Focal point falls before the retina
  • Leans forward to see/read
  • Eyeball is long and lens is too strong
  • BICONCAVE LENS (spherical) to correct
• Farsightedness/Hyperopia


  • Focal point falls after the retina
  • Leans away to see/read
  • Eyeball is too short and lens is weak
  • BICONVEX LENS (spherical) to correct
• Refractive errors depend upon the lens and the axial length of the eyeball
• Myopia


  If the eyeball is LONG, the focal point falls before the retina
• Hyperopia


  If the eyeball is shorter than normal, focal point falls behind the retina
• Lens


  • If the lens is very strong, light rays will be bent immediately= MYOPIA
  • If the lens is very weak= HYPEROPIA
• Astigmatism


  • Problem in either the cornea or the lens
  • "Uka-uka" ang cornea or lens (uneven curvature of the cornea or lens)
  • Oblong-shaped cornea
  • Multiple focal points which are dispersed within the eye
  • CYLINDRICAL LENS (to concentrate the points into 1 focal point)
• Oldsightedness/Presbyopia


  • Images fall in front or behind the retina
  • Inelastic lens (begins @ age 14; complete inelasticity @ 40 y/o) and denatured proteins in the lens
  • BIFOCAL or PROGRESSIVE LENSES