Anatomy & major eye diseases : Anatomy & major eye diseases Ocular Anatomy : Ocular Anatomy Overview of the eye:
Retina Part 1: Structures around the eye : Part 1: Structures around the eye External eye - Conjunctiva : External eye - Conjunctiva Thin mucus membrane covering the sclera
Acts as a lining for upper and lower lids
Function: Important in tear film and mucus formation to keep the eyes clean and moist Conjunctiva : Conjunctiva Thin mucus membrane extending from the limbus posteriorly covering the anterior part of the sclera
Then the conjunctiva is reflected at the fornix to cover the inside of the upper and lower lids
The folding of conjunctiva between the eye ball and eye lid creates a bag like structure called the conjunctival sac Slide 6: Conjunctivitis Tearfilm : Tearfilm Produced by the tear & other glands
A layer of water, oils and nutrients that flow over the exposed surfaces of the eye
Approximately 0.5ml/1.0ml of tears are produced each day
Virtually no tears are produced during sleep
Function: Keep the eye moist, clean, & form a smooth refractive surface Tear film structure & function : Tear film structure & function Slide 9: Tear Flow Eyelids & Tears : Eyelids & Tears Slide 11: Part 2: THE EYE - Anatomy Slide 12: Cornea
Transparent; No blood vessels
Endothelium critical to transparency (viscoelastics for protection)
The shape of the cornea directly impacts visual acuity
Function: major refractive structure of the eye (+45D)
The junction between Sclera & Cornea is called Limbus Outer Fibrous Layer : Cornea + Sclera The CorneaGauging the Corneal Diameter : The CorneaGauging the Corneal Diameter Corneal structure : Corneal structure Epithelium
Endothelium Outside: Tear Inside: Aqueous Humour Corneal physiology : Corneal physiology Epithelial cells are tightly joint together & highly regenerative. They serve as a natural barrier towards micro-organism invasion to the cornea.
Cornea is transparent because of the highly regular line up of collagen fibres
Wound / ulcers penetrating the Bowman’s membrane results in new collagen fibre formation which does not have the regular pattern – scar formation. Corneal physiology : Corneal physiology Endothelial cells is responsible for maintaining the water balance & thus transparency of the cornea.
Hypoxia (lack of oxygen) can result in reduced endothelial activities and the cornea will swell (edema), causes haziness and new blood vessel formation both affecting corneal transparency Corneal Edema Corneal New Vessel Corneal Physiology : Corneal Physiology Oxygen necessary to maintain transparency and avoid hypoxic stress
Hypoxia = reduced oxygen levels
CL wear may compromise oxygen availability Corneal Physiology : Corneal Physiology Corneal oxygen supply
Atmosphere (21% oxygen @ sea level)
Limbal blood vessels
Palpebral and limbal blood vessels (7% oxygen)
Aqueous humor Corneal Physiology : Corneal Physiology Hydration dynamics
The stroma is a “sponge,” freely absorbing water
Bounded by two cell layers designed to maintain water content at ~78%
Endothelium cells contain active “pumps”
Cornea swells when pumps can’t keep up with inflow of water from tearfilm Why the Cornea Swells : Why the Cornea Swells Epithelium responds to hypoxia by producing excess lactate
Lactate enters stroma and changes pH/osmolarity
Change in osmolarity pulls H2O into stroma
Results in corneal swelling (edema) Sclera : Sclera “The White of the Eye”
Function: Protective layer of the eye
Also collagen fibres No regular patterns
Tendons of extra-ocular muscles blend with it for insertion Uvea : Uvea The middle vascular layer of eye, uvea, consists of 3 structures:
Iris (11 – 13 mm) and Pupil (3 – 4 mm)
Ciliary Bodies & Zonules
Choroid Iris & pupil : Iris & pupil Function: Control the amount of light entering the eye by adjusting the pupil size
Circular shaped diaphragm containing 2 sets of muscles to control the pupil size. (circular & radial muscles) With pigment & non-pigmented cells.
Many pigments = 'brown eyes';
some pigments = 'green eyes‘;
very few pigments = 'blue eyes‘
The pupil should be equally big & round and respond both to light & accommodation Uvea: Ciliary Body : Uvea: Ciliary Body Function: Increase refractive power to help focusing at near (accommodation); produce aqueous humour
Contraction of ring shape ciliary muscle causes the ciliary body to move anteriorly. Lens : Lens Second major refractive component of the eye (20D, ~30% of total power)
Elastic nature helps focusing at different distances
Lens grows with age Capsule Nucleus Cortex Uvea: Choroid : Uvea: Choroid Thin, spongy, highly vascular, dark brown, layer.
Function: Important to provide nutrition to the inner eye (retina) Slide 27: SCLERA CHOROID RETINA VITREOUS Retina Inner layer of eye that contains 10 layers & 120 millions
photoreceptors & over 1 Million nerve fibres.
Function: Transform light energy to electrical signals Retina: macula & fovea : Retina: macula & fovea Macula (macula lutea and fovea centralis).
At posterior pole of eye
It is called the Macular Lutea because it contains a lot of Lutein: a yellow substance which is a form of Vitamin A to protect the macular from free radical damages due to high energy radiation
Spot of most acute vision.
Fovea: Small shallow depression in the center of macula caused by almost complete absence of inner retinal layers.
Rods absent and only cones. Examination of the Retina : Examination of the Retina Direct Ophthalmoscopy Optic Nerve : Optic Nerve Carries visual impulses from the retina to the brain
Consist of 1 Million Nerve Fibres Common eye diseases - Anterior : Common eye diseases - Anterior Superficial
Conjunctiva – Conjunctivitis, Hemorrhage
Cornea – Keratitis, Corneal Ulcer
Eye lid – Ptosis, Trichiasis, Blepharitis, Hordeolum (Stye)
Glaucoma – Abnormal Intra-Ocular Pressure
Cataract – The crystalline lens turns opaque
Iritis– Inflammation of the Iris Glaucoma : Glaucoma Normal range : 12 – 16 mm Hg
IOP of 21 mm Hg or above is highly suspicious The AOA definition : a group of ocular diseases with various causes
that ultimately are associated with a progressive optic neuropathy
leading to loss of visual function Cataract : Cataract Cataract – cloudy of the lens that blocks some light from reaching the retina & interfering with vision. Common eye diseases – Posterior Segment : Common eye diseases – Posterior Segment Vitreous – degeneration causes floaters. Common & usually harmless, however, sudden onset or worsening can mean serious retinal problem. Degenerated vitreous can cause traction on the retina resulting in retinal detachment. Common eye diseases – Posterior Segment : Common eye diseases – Posterior Segment Retina
– Retinal degeneration (causing retinal holes and retinal detachment). Strongly associated with high myopia.
– Retinal hemorhage (diabetes, hypertension or a hit at the head or the eye) Thank You : Thank You