Week 3 - Vision disorders

Cornea

Clear layer that refracts light and focuses towards the retina

Anterior chamber

Contains aqueous fluid for nutrition to the cornea and lens

Iris

Posterior to the anterior chamber

Pupil

Controls light entering eye

Lens

Behind the pupil and capable of changing shape until it can’t accommodate with old age

Vitreous cavity

Gel like fluid that helps to maintain the structure of the eye

Retina

Receives light and processes it through the axons to the optic nerve

Optic disc

Nerve fibre layers exit the eye out of the optic nerve

Layers of the retina

Ganglion cells → Photoreceptors → Retinal pigment epithelium → Choroid

Steps of the visual pathway

1) Optic nerve: Carry signals from the eye to the brain
2) Optic chiasm: Where the optic nerves cross
3) Lateral geniculate nucleus: Relay center for visual information
4) Visual cortex: Visual information to see

Myopia

Near vision is better than distance vision

Hypermetropia

Distance vision better than near vision

Astigmatism

Due to irregular shape of cornea; distorted image

Presbytopia

Reduce ability to focus on near vision tasks that deteriorate with age

How do beta blocks manage glaucoma?

Reduce the production of aqueous humor

How do alpha agonists manage glaucoma?

Drugs decrease aqueous humor production and increase its outflow

Trabeculoplasty for glaucoma

Laser procedure directly to the drainage pathway to improve drainage of aqueous humor

Trabeculectomy for glaucoma

Surgically create a new drainage pathway for the aqueous humor to lower IOP

Gene therapy in vision disorders

Gene (RPE65) is inserted into a adeno-associated virus (AAV) vector → administered to the patient through suprachoroidal injections

Challenges of gene therapy

Difficult delivery, high cost, immunogenicity

Stem cell therapy for vision disorders

Cell replacement, neuroprotection (release growth factors and cutokines that protect exisiting retinal cells), anti-inflammatory effects

Challenges of stem cell therapy

Risk of tumors, immune rejection, cell survival

Function of a visual acuity test

Assess clarity of central vision

Function of visual field testing

Identify defects in peripheral vision and localise visual pathway dysfunction

Function of a fundus examination

Assessment of the retina and optic nerve for structural abnormalities

Function of intraocular pressure measurement

Iedntify elevated IOP

Function of pupillary reaction testing

Assess the pupillary light reflex and provide information about the integrity of the optic and oculomotor pathways

Proliferative diabetic retinopathy

Formation of new, abnormal blood vessels on the retina