Lecture 6 and 7 Flashcards
Extraocular muscle disfunctions
1) Strabismus
2) Amblyopia
Strabismus
- Cross-eyed
- Weakening or misalignment of the eye’s muscles
- can lead to amblyopia
- double vision, loss of depth perception
-motor over sensory
-Causes: Genetic (children), Stroke, Brain tumor
-Treatments: Surgery, Corrective Lenses, Eye Exercises, Botox
Amblyopia
- Lazy eye
- The weakening of one eye’s input into the brain
-Without as much sensory input the position of the weaker eye will wander. This will lead to misalignment
-Blurred vision
-Weak eye losses brain connectivity
-Sensory > Motor
-Causes (in 1 eye): high refractive error, deprivation (opacity of corneal or lens)
- Treatments: Corrective lenses, cataract surgery, deprivation of “strong” eye.
Corneal diseases
1) corneal abrasions / injury
2) Keratitis (infections)
3) Keratoconus (thinning)
Corneal abrasions / injury
Like the skin, any physical or chemical injury will leave the cornea damaged, scaring can lead to permeant injury and loss of vision
Keratitis (infections)
Both bacteria and other microbes can infect the cornea and conjunctiva surrounding the sclera.
Example: Acanthamoeba can infect the cornea (rare; associated with contact lens use).
Keratoconus (thinning)
Corneal thinning is rare but can cause
changes in how light is refracted into the eye leading to blurry vision.
Thinning of the cornea can lead to bulging (see image).
Types of cornea transplants
Keratoplasty –
transplant from donor tissue
Keratoprosthesis -Transplant with prosthetic cornea
Coloboma
- Misshapen iris caused by development errors
-Colobomas can affect other eye structures
▪ Eyelid coloboma
▪ Lens coloboma
▪ Retinal/macula coloboma
▪ Optic nerve coloboma
▪ Uveal/Iris coloboma - Causes of coloboma
▪ Genetic, inheritance
▪ Alcohol exposure during pregnancy
-Treatments (not many options)
▪ Contact lenses, cosmetic
▪ Amblyopia correction; eye patch.
Stages of early development:
1) bud off the forebrain
2) Begin fold into a cup shape
3) steal the cup shape
Key points of the lens and why it is clear / transparent:
1) The cells in the central lens do not have a nuclei and organelles
2) The cells in the central lens consist of a structural protein called crystalline
Cataracts
Cataracts – a clouding of the lens, reducing transparent, and reducing vision.
Symptoms:
* Blurry vision
* Difficult with vision in dim light
* Halos around lights
* Can not be corrected by eyeglasses
Age is a major contributor (50% of adults over the age of 75 have cataracts)
Other Risk Factors:
* UV exposure
* Smoking
* Diabetes
* Previous eye disease or trauma.
* Radiation or chemotherapy.
* Genetics
Mechanisms for cataracts formation:
-Aggregation of crystalline (crystallin is normally soluble but aggregates together during cataracts formation)
Treatment for cataracts removal
There are no drug treatments for cataracts other than surgery to remove and replacing the cataract with an artificial lens.
Goals of Cataract surgery:
1) Remove the old lens in small pieces.
2) Replace the old lens with a new artificial intraocular lens (IOL).
Types of refractive errors of the eye
1) Myopia (Nearsightedness)
2) Hyperopia (farsightedness)
3) Astigmatism
4) Presbyopia
Myopia
Nearsightedness
- Far away objects look blurry
- the focal point of light lands short of the retina.
Causes:
-Elongation of the eye.
* Incorrect cornea curvature.
* Defects in lens optics
Hyperopia
Farsightness
-Images close-up will be blurry
-the focal point of light lands beyond of the retina.
Causes:
* Shortening of the eye.
* Incorrect cornea curvature.
* Defects in lens optics
Astigmatism
Causes blurry vision for images close-up and far-away. It can also
cause double vision
(can cause blurriness in horizontal or vertical direction)
Causes:
* Irregular cornea shape.
* Lens aberrations
Presbyopia
-Difficulties seeing close-up associated with middle-age (>45 years old)
- Similar to hyperopia (farsightedness).
- Cause the lens becomes less flexible with age and cannot be easily rounded to focus on objects close-up.
Retinal Tears and Detachment
-occur when the retina is separated from choroid.
-Without surgical repair, these retinal injuries can lead to permeant vision loss.
-Vision symptoms include perception of a dark curtain and floaters
- Vitreous humor can pull on the retina leading to tears and detachment
Causes of Retinal Tears and Detachment
Causes:
* Trauma/injury.
* Age – vitreous humor volume shrinks and pulls on retina.
* Diabetes – Scar tissue can form stiffening the retina and increasing the chance of a tear.
* Macular degeneration – vitreous humor can build up behind the retina.
Age-related Macular Degeneration (AMD)
Symptoms:
* Loss of the central visual field
* Distorted vision.
* Cloudy vision.
Prevalence (>40 years old):
* ~10% with early-stage AMD
* ~0.9% with late-stage AMD
Types of AMD
1) Dry AMD
* Drusen formation
* Some vision loss
* Photoreceptor atrophy
2) Wet AMD
* Presence of blood in the macula
* A potential complication in late-stage AMD.
* Significant Photoreceptor
degeneration.
Stages of AMD
- Build-up of “cell junk”
- “Cell junk” aggregates into a drusen.
- Atrophy of RPE and Photoreceptors
- (Wet Only) Break-down of Choroid-Retina barrier
leads to neovascularization.
Common treatments for AMD
Early-stages “Dry” AMD
AREDS 2 Multi-Vitamin
“Wet” AMD
Anti-VEGF drugs
(inhibit blood vessel growth)
Retinitis pigmentosa (Retina pigmentosa, RP)
Symptoms:
* Loss of night vision
* Gradual loss peripheral vision
* Causes “tunnel vision”.
* Problems with color vision.
Prevalence:
* Occurs in 1:3000 – 1:5000 births
* Inherited (genetic)
Molecular genetics of Retinitis Pigmentosa (RP)
- > 100 gene mutations linked to
retinitis pigmentosa. - Some genes are associated with
other disorders, such as Usher
Syndrome (Ush2a). - RP genes encode for proteins
important for rod photoreceptors
or retina pigment epithelium.
Disease mechanisms in retinitis pigmentosa
- Cellular etiology (cause or origin) of RP depends on the gene mutation:
1) Retinal cycling/metabolism.
2) Phototransduction
3) Photoreceptor structure.
4) Nuclear transcription/splicing
What are the differences between AMD and RP
Age-related Macular Degeneration
* Central retina degeneration
* Cone degeneration
* Common
* Occurs later in age.
* Major cause is age.
Retinitis pigmentosa
* Peripheral retina degeneration
* Rod and Cone degeneration
* Rare
* Occurs at birth and throughout life.
* Major cause is genetic.
Rhodopsin
is the light-sensitive protein that converts photons of light into a chemical signal.
- Rhodopsin uses the organic molecule retinal to sense photons of light.
- The change from cis retinal to trans-retinal after light stimulation causes a conformation change in the rhodopsin protein.
Different opsins sense light in rods and cones
3 Opsins (color) and 1 Rhodopsin (dim light)
Color vision deficiency (colorblindness)
- Colorblindness occurs when you are unable to see color in a normal way.
- It does not affect the sharpness of vision.
Types of color vision deficiency
Red-Green Color Deficiency
* Difficulties distinguishing between green and red.
* Subtypes: Deuteranomaly, Protanomaly, Deuteranopia, and Protanopia
* Gene mutations: OPN1MW and OPN1LW (X-linked)
Blue-Yellow Color Deficiency
* Difficulties distinguishing several different colors (blue-green; yellow-red)
* Subtypes: Tritanomaly, Tritanopia
* Gene mutations: OPN1SW
Complete Color Deficiency
* No color vision, increased sensitivity to light
* Subtypes: monochromacy or achromatopsia
Optic neuropathies disrupt…
the function and integrity of the optic nerve
Symptoms and Prevalence of Glaucoma
Symptoms:
* Loss of peripheral vision
* Eye redness
* Eye pain & headaches
Risk Factors:
* Age
* Family History (genetic)
* Higher incidence among Hispanic
and African Americans
Mechanisms of Glaucoma Progression
Disease Stages:
1) Elevation of intraocular pressure
2) Compression of optic nerve head
3) Axon degeneration of retinal ganglion cells
4) Retinal ganglion cell death.
Main types of Glaucoma:
1) Angle-closure Glaucoma – when there is a blockage between the iris and lens.
2) Open-angle Glaucoma (most common) – when there is a blockage of the
trabecular meshwork or Schlemm’s canal.
Treatments for glaucoma:
1) Angle-closure Glaucoma:
* Pilocarpine – relaxes muscles that may cause blockage
* Surgery
2) Open-angle Glaucoma:
* Drugs to reduce vitreous humor creation
* Surgery
Other types of optic neuropathies
1) Optic neuritis
2) Nutritional / Toxic optic neuropathy
3) Diabetic Retinopathy
4) Leber’s Hereditary Optic Neuropathy (LHON)
5) Neuromyelitis optica
