Optho part tressss Flashcards
Anatomy of lens
- Intraocular location of lens behind the iris plane – contained within the lens capsule
2. Optical clarity of the normal lens – typically the lens is optically clear at birth, but with aging it slowly becomes opaque, generally advancing from yellow, to brown to white. When the lens becomes opacified it is referred to as a cataract.
3. Suspension of normal lens in retroiridic position by zonules – this allows the lens to change shape in response to changes in the ciliary body.
Why do we have a lens? What is its function?
4. Presbyopia - a condition where the eye exhibits a progressively diminished ability to focus on near objects with age. Presbyopia’s exact mechanisms are not known with certainty; the research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens’s curvature from continual growth and loss of power of the ciliary muscles (the muscles that bend and straighten the lens) have also been postulated as its cause. Like gray hair and wrinkles, presbyopia is a symptom caused by the natural course of aging. The first signs of presbyopia – eyestrain, difficulty seeing in dim light, problems focusing on small objects and/or fine print – are usually first noticed between the ages of 40 and 50.
Symptoms attributable to cataract
- Slowly progressive blurring of vision
2. Painless progressive loss of vision – most often noticed at night. One of the earliest symptoms is the presence of increased glare from point sources of light (headlights on cars).C. Examination of lens by direct ophthalmoscopy
1. Evaluation of the red reflex
Examination of lens by direct ophthalmoscopy
- Evaluation of the red reflex
Abnormal lens feat General
a. loss of normal red reflex – this is often discovered by the primary care provider, this is usually a sign of an advanced cataract.
b. Dark spots in red reflex – often a sign of a moderate nuclear cataract where the red reflex appears “missing” centrally (like a donut).
c. Abnormal color of red reflex – can appear more orange or yellow in one or both eyes.
Lens abnormalities found in important systemic diseases :Marfan’s syndrome
due to mutations in the fibrillin gene, the lens is frequently displaced. The condition is bilateral, symmetric and non-progressive. Often good functional vision is intact, however when vision is impaired an artificial intraocular lens implant may prove beneficial.
Lens abnormalities found in important systemic diseases: Implantation of artificial intraocular lens
most lens based abnormalities (primarily cataracts) are treated by phacoemulsification (using ultrasound to break up and remove the lens) with intraocular lens implantation. Most modern lenses are placed in the same position as the physiologic lens inside the lens capsule. When the lens capsule is damaged or un healthy an intraocular lens can be placed in the sulcus between the lens capsule and posterior iris or in the anterior chamber resting on the anterior surface of the iris.
Neuro-Ophthalmology Anatomy
Afferent visual pathways – retina -> Optic nerve -> chiasm -> optic tract -> optic striations -> occipital lobe
Neuro-Ophthalmology Anatomy: Trigeminal nerve
Cranial nerve V, provides sensory innervation to the cornea and eyelids, clinically relevant in Herpes Zoster Ophthalmicus
Neuro-Ophthalmology Anatomy: Facial nerve
provides motor innervation to the orbicularis oculi, important for adequate lid closure and clinically relevant in Bell’s Palsy
Ocular autonomic pathways: sympathetic pathways
– important for pupil dilation, travels a circuitous route involving the superior cervical ganglion, this is the pathway that is disrupted in Horner’s syndrome
Ocular autonomic pathways: : parasympathetic pathways
important for pupils constriction, travel with the third cranial nerve, this pathway can be disrupted by an aneurysm in the circle of Willis (specifically the posterior communicating artery). It is important to understand this anatomy in the evaluation of a third nerve palsy.
pupillary pathways
– the light reflex consists of four neurons. The first connects the retina to the pre-tectal nucleus (these decussate in the chiasm). The second connects the pre-tectal nucleus to both Edinger – Westphal nuclei. The third connect the Edinger-westfal nucleus to the ciliary ganglion. Fourth from the ciliary ganglion to the pupil.
- Pupillary disorders: Dilated pupil
Unilateral – concern for third nerve palsy
Bilateral - pharmacological
Pupillary disorders: Adie’s tonic pupil
caused by denervation of the postganglionic supply to the sphincter pupillae and the ciliary muscle, thought to be caused by a viral illness. It typically affects young adults, and is almost always unilateral. The affected pupil is generally large and regular, and the light reflex is absent. It can be associated with diminished deep tendon reflexes or autonomic nerve dysfunction.
Pupillary disorders: Relative afferent pupillary defect
a condition in which the optic nerves conduct in an asymmetric fashion, most likely due to pathology affecting one optic nerve. Generally detected by the swinging flashlight test.
