Sight - Special Senses Flashcards
What is the function of the eyebrows?
shade; inhibit sweat
What is another name for eyelids?
Palpebrae
What is the Palpebral fissure?
space or distance between eyelids
What are the Canthi? (What is a canthus?)
the outer or inner corner of the eye, where the upper and lower lids meet
What is the Lacrimal caruncle
a modified sweat and sebaceious gland at the medial canthus (inner corner of your eye)
a small, pink, globular bump in the inner corner of the eye
What is Conjunctiva and Conjunctivitis?
a thin, clear membrane that lines the inside of the eyelid and covers the white of the eye
when inflammed it is called Pinkeye
What is Palpebral conjunctiva?
inner surface eyelids
What is Bulbar conjunctiva?
The transparent membrane on the anterior white surface of the eye, except over the pupil
Describe eyelashes, what kinds of glands do they have?
double/triple row of hairs with Ciliary glands and Meibomian glands.
Ciliary glands (modified sweat glands), produce a water secretion that contributes to the tear film, helping to keep the eyes moist and lubricated, and empty into hair follicles.
The inner margin of the eye lid contains Meibomian glands that produce sebum, an oily substance that coats the eyes and prevents tears from evaporating
Together, these glands ensure a smooth, moist environment for proper eye function and protect the cornea from irritation and dryness.
What are Meibomian glands, what do they secret and why?
oil glands in the eyelids that produce meibum, an oily substance that coats the eyes and prevents tears from evaporating
Describe the Lacrimal Apparatus, where are tears produced and where do they go?
- Tears are produced in the lacrimal gland located above the eye and exit the gland through several lacrimal ducts;
- Tears enter the conjctival sac and run across the eye towards the nose
- Tears enter the lacrimal canliculi in the corner of the eye
- Tears drain in the lacrimal sac
- Tears travel down the nasolacrimal duct
- Tears enter the nasal cavity
This is why a person’s nose runs when he or she cries.
Additionally, the tears wash foreign objects away from the eye.
What are the 3 layers of the eye?
- The Fiberous Layer (outer most layer)
- The Vascular Layer (middle layer)
- The Retina (Nervous Layer) (inner most layer)
Describe the Fibrous layer (there are 2 main parts)
The outer layer
- Sclera:
- the white outer layer of the eye.
- Maintains shape, protects internal structures, provides muscle attachment point.
- continuous with cornea. - Cornea:
- It is called window of the eye.
- It is the extension of the sclera that covers the anterior eye over the iris.
- It has connective tissue matrix containing collagen, elastic fibers and proteoglycans.
- It is Avascular, transparent, and allows light to enter eye.
- When accumulated with increased fluid, it results in scattering of the light rays.
Describe the Vascular layer (describe the 4 main parts as well as the 3 intrinstic muscles involved)
the Middle layer
- Choroid:
- very thin and pigmented with melanin.
- contains most of the blood vessels of the eye: branches off the internal carotid arteries; - Iris:
- is the colored part of the eye
- Controls light entering the pupil. - Pupil:
- is the hole in the middle of the iris. Smooth muscle from iris determines size of pupil such as:
Sphincter pupillae: that constricts the pupil when light is too bright and is under the parasympathetic nervous system
Dilator pupillae: that dilates the pupil when light is too dim under sympathetic nervous system
- Ciliary body:
Ciliary Muscle is a smooth muscle that controls the lens shape.
- when the ciliary muscle contracts, the ciliary zonules loosen, allowing the lens to bulge for close vision (accommodation).
Ciliary processes produce aqueous humor, which fills the anterior chamber providing nutrients and maintaining intraocular pressure
Describe the Nervous Layer (what are the 2 layers that make up the nervous layer?)
The Retina:
a thin layer of tissue located at the back of the eye, lining its inner surface. It plays a crucial role in vision by capturing light that enters the eye and converting it into electrical signals that are sent to the brain via the optic nerve
The Retina has 2 Layers:
- Sensory Layer:
- inner layer containing photoreceptors: rod and cone cells sensitive to light
- A network of neurons, including bipolar cells and ganglion cells, which process and transmit visual information
- Rods and cones synapse with bipolar cells that synapse with ganglion cells in all areas except the fovea. - Pigmented Layer:
- outer, pigmented layer; pigmented simple cuboidal epithelium;
- Pigment of this layer and choroid help to separate sensory cells and reduce light scattering
The macula is the central part of the retina responsible for sharp central vision.
The fovea, located within the macula, contains a high concentration of cones for detailed vision and no rods
Describe the segments(compartments) and chambers of the eye.
Anterior segment:
- anterior to lens; filled with aqueous humor.
- This humor is reabsorbed by the scleral venous sinus (Canal of schlemm).
- Helps maintain intraocular pressure; supplies nutrients to structures bathed by it; contributes to refraction of light. An increase in the intraocular pressure due to inhibition in the circulation of aqueous humor leads to the condition, Gluacoma.
– Anterior chamber: is located between cornea and iris
– Posterior chamber: is located between iris and lens
Posterior Segment:
- larger and is located between the lens and retina
- It contains more viscous and jellylike substances, the Vitreous body; that maintains eye shape as well as intraocular pressure.
- Also, it helps hold the lens and retina in place.
Describe the Lens
focuses light on the retina. It changes shape as ciliary muscles contract and relax
How does Focusing work?
Pupil Size and Depth of Focus:
- The depth of focus refers to the range over which an object remains in focus on the retina.
- A smaller pupil increases depth of focus by reducing optical aberrations and improving sharpness, similar to the aperture effect in photography.
Role of the Ciliary Muscle:
- The ciliary muscle changes the shape of the lens to adjust focus for near or distant objects (accommodation).
- When the ciliary muscle contracts, the lens becomes more rounded for near focus. When it relaxes, the lens flattens for distant focus.
Relation Between Pupil and Accommodation:
- The pupil often constricts during accommodation for near objects (a phenomenon called the near reflex), which also increases depth of focus.
Far distant vision
point at which lens does not have to thicken to focus.
20 feet or more from eye
The ciliary muscles are relaxed
Near distant vision
to focus on object Closer than 20 feet ciliary muscles must contract and changes occur in the lens.
Describe Rods
- Photoreceptor cells for black and white vision.
- They are found over most of retina, but not in fovea.
- More sensitive to light than cones.
Rhodopsin and Light Sensitivity:
- Rods contain the protein rhodopsin, which is a light-sensitive pigment. When struck by light, rhodopsin undergoes a conformational change, separating into opsin and retinal (a derivative of Vitamin A).
- In darkness, opsin and retinal recombine to regenerate rhodopsin, restoring the rod’s sensitivity to light.
Vitamin A Connection:
- Retinal is derived from Vitamin A, and it can be converted back to Vitamin A when needed for the regeneration of rhodopsin.
Depolarization and Hyperpolarization:
Dark = depolarization of rods
Light = Hyperpolarization of rods
- Rods are unusual sensory cells because they are depolarized in darkness
(due to the constant influx of sodium ions through cyclic GMP-gated channels (the “dark current”) - Light triggers a cascade that lowers cyclic GMP levels, closing the sodium channels, which causes the rod to hyperpolarize.
Role of Transducin:
- The protein transducin is activated during the phototransduction process. Light causes 11-cis-retinal to convert to all-trans-retinal, which activates transducin.
Signal Transmission:
- The signal is transmitted from the rods to the bipoliar cells to ganglion cells, which send the information to the brain via the optic nerve.
Light and Dark Adaptation:
- The eye adjusts to changes in light levels through light and dark adaptation, which involves changes in the amount of available rhodopsin.
- In bright light, rhodopsin is bleached (broken down), reducing rod sensitivity. In darkness, rhodopsin regenerates, increasing sensitivity.
Light and Dark Adaptation:
Rods: in bright light, rhodopsin is broken down into Vitamin A, protecting the eye and making it less sensitive to light.
In darker conditions, more rhodopsin is produced so the eye is more sensitive to light.
It takes eyes a while to accommodate when going from dark to light and vice versa because of these chemical changes that must occur.
Note: light and dark adaptation actually involves pupillary reflexes, variations in rod and cone functions and changes in the amount of available rhodopsin.
Pupils: constriction in bright light; dilation in dim light.
Describe Cones
Photoreceptor cells responsible for color vision and visual acuity.
– Numerous in fovea and macula lutea; fewer over rest of retina.
– As light intensity decreases so does our ability to see color.
– They contain iodopsin, and the three types of cones (blue, green, and red) work together to interpret millions of colors through their overlapping responses to light.
Optic Disc
The Blind Spot
Blood vessel the optic nerve enters / exits the eye here causing a blind spot in the eye.
Fovea centralis
is the area of greatest or highest visual acuity
located in the macula lutea
contains only cones and no rods
Myopia
Nearsightedness
The focal point of light entering the eye is too close to the lens, causing the image to be focused in front of the retina rather than directly on it
Due to elongated eyeball
Hyperopia
Farsightedness
Image is focused behind retina due to short eyeball
Presbyopia
Degeneration of accommodation due to age, corrected by reading glasses
Astigmatism
Cornea or lens not uniformly curved
Strabismus
Lack of parallelism of light paths through eyes
Retinal detachment
Can result in complete blindness
Glaucoma
Increased intraocular pressure by aqueous humor buildup
