Week 7

Question 1

Simple structure of eye?

Answer 1

Sclera
Pupil
Iris

Question 2

Diopteres?

Answer 2

measure of lens focussing power

1d = 1m away

Question 3

*Phototransduction?

Answer 3

Bleaching - Light changes rhodopsin, separating retinal and opsin.

Hyperpolarization - Opsin activates PDE via G-protein, reducing cGMP and closing Na+ channels

Signal Transmission - Reduced neurotransmitter release affects bipolar and ganglion cells, modulating signals to the brain.

Question 4

Ciliary muscles?

Answer 4

Control the shape of the lens in the eye, allowing it to change focus. When the muscles contract, the lens becomes more rounded and shortens, increasing power for near vision. When they relax, the lens flattens for distant vision. This process is known as accommodation.

Question 5

Myopia?

Answer 5

Aka nearsightedness.
It is a vision condition where distant objects appear blurry because the eye focuses light in front of the retina, often due to an overly long eyeball or excessive curvature of the cornea.

Question 6

Hypermetriopia?

Answer 6

Aka farsightedness.
It is a vision condition where close objects appear blurry because light is focused behind the retina. This often occurs due to a short eyeball or a weak cornea/lens.

Question 7

Presbyopia?

Answer 7

Age-related condition where the eye’s lens loses its ability to change shape (accommodation), making it difficult to focus on close objects. This typically occurs around age 40 and is often corrected with reading glasses

Question 8

*Role of the Pupil?

Answer 8

The pupil adjusts in size from 2 to 8 mm, controlling light intake by about 16 times. This is the primary response to changing light, but it contributes only a small part of the eye’s overall light adaptation as other mechanisms like retinal adaptation also play significant roles.

Question 9

The pupillary muscles?

Answer 9

Sphincter pupillae
Dilator

Question 10

*Benefits of smaller pupil size?

Answer 10

Less light reaching retina

Greater depth of field (more focus)

Reduced spherical abberation

Reduced glare (scattering of light)

Infinite depth of field

Compensates for myopia

Question 11

*Retina cell types?

Answer 11

Photoreceptors, horizontal,
amacrine, bipolar and ganglion cells

Question 12

*Structure of Retina?

Answer 12

Consists of layers: photoreceptors (rods and cones), bipolar cells, and ganglion cells

Question 13

Design flaw of retinas?

Answer 13

Photoreceptors are at the back of the retina, so light scatters as it passes through other cell layers, reducing efficiency.

Question 14

Why is the fovea structure how it is?

Answer 14

Structures in front of foveal receptors are pushed to one side.
Reduces light scatter/absorption, thereby increasing acuity.

Question 15

Rods and cones?

Answer 15

Rods - Responsible for vision in low light (scotopic vision) and are highly sensitive to light but do not detect color.

Rods are most densely packed in the periphery of the retina, with the highest concentration around the fovea’s outer region, but they are absent in the central fovea

Cones - Cones are responsible for color vision and detailed vision (photopic vision) in bright light.

Cones are concentrated in the fovea, the central part of the retina, providing high visual acuity. The fovea contains almost exclusively cones, with the density decreasing in the periphery.

Question 16

Rhodopsin?

Answer 16

Rhodopsin is a light-sensitive pigment in rod cells that enables low-light vision. It consists of the protein opsin and the molecule retinal. When light hits rhodopsin, retinal changes shape, activating the protein and triggering a signal to the brain. This process is essential for vision in dim light and requires regeneration of rhodopsin after each use.

Question 17

*Phototransduction?

Answer 17

Photopigment Bleaching: Light photons trigger a change in rhodopsin (the combination of retinal and opsin in rods), causing retinal and opsin to separate, resulting in the bleached state.

Cell Membrane Hyperpolarization: Opsin activates phosphodiesterase (PDE) through the G-protein transducin, converting cGMP to GMP. This closes Na+ channels, causing hyperpolarization as K+ continues to leak out.

Neural Output: Hyperpolarization reduces glutamate release, affecting the bipolar cells’ membrane potential. This modulates the ganglion cell’s firing rate, with bipolar cells acting either excitatory or inhibitory, influencing visual signal processing.

Question 18

*Visible range of luminance?

Answer 18

Human vision functions across ~ 10^15 units of luminance

Question 19

*Scotopic versus Photopic vision?

Answer 19

Scotopic
low light vision
Rods only
High sensitivity/low acuity
Non-foveal

Photopic
Suited for high luminance
Cones only
Lows sensitivity/high acuity
Foveal & peripheral

Mesopic
Intermediate luminance (e.g. Dusk)
Rods & cones
Intermediate sensitivity/acuity
Foveal & peripheral

Question 20

*Adaptation of eye?

Answer 20

Pupil size - changes diameter to control light, smaller pupils enhancing depth of field and reducing scatter, larger allows for better lower light conditions

Rod/cone switch - In low light, rods dominate, providing high sensitivity but low acuity (scotopic vision).
In bright light, cones take over, offering high acuity and color vision (photopic vision).
Mesopic vision occurs in intermediate light, where rods and cones work together.

Photopigment regeneration - Photopigments (e.g., rhodopsin in rods) are constantly bleached (broken down by separating retinal and opsin) by light exposure and then regenerated in darkness (combine retinal and opsin).

Light adaptation (calcium regulation). - Quick changes in sensitivity (~seconds) occur when transitioning between light levels.
Prevents receptor saturation in bright light and maintains functionality through calcium-mediated automatic gain control within photoreceptors.

Dark Adaptation - After moving from bright to dark environments, the eye gradually increases sensitivity over ~20 minutes.
Cones adapt quickly but have higher thresholds, while rods adapt slower but achieve much greater sensitivity.

Question 21

*Color Vision?

Answer 21

Human vision relies on three types of cones, each sensitive to different wavelengths:
S-Cones: Short wavelengths (blue).
M-Cones: Medium wavelengths (green).
L-Cones: Long wavelengths (red).

These cones work together to perceive a wide range of colors.

Colors are processed in opposing pairs:
Red-Green, Blue-Yellow, and Black-White.

Color blindness results from cone defects or absence

Question 22

*Visual Pathways?

Answer 22

Information travels via the optic nerve and lateral geniculate nucleus to the visual cortex.

Question 23

*Definition of Proprioception?

Answer 23

Proprioception is the sense of body position and movement, involving muscle spindles and Golgi tendon organs. It is highly sensitive for balance and integrates with vision and vestibular input.

Question 24

*Muscle Spindles?

Answer 24

Muscle spindles, lying parallel to extrafusal fibers, detect muscle stretch and velocity. Through alpha-gamma coactivation, they maintain sensitivity during muscle contraction, ensuring accurate feedback for posture, movement, and reflexes

Question 25

*Golgi Tendon Organs?

Answer 25

Golgi tendon organs detect muscle tension and help prevent overload by signaling the nervous system through group Ib afferents. When excessive tension is detected, they trigger an inhibitory response to reduce muscle activity, preventing injury or damage from overloading.

Question 26

*Interlink of sensory and force production?

Answer 26

Muscle spindles detect changes in length and velocity, while Golgi tendon organs sense tension, and both contribute to fine-tuning force production to prevent injury and optimize performance. This feedback loop ensures muscles can produce the right amount of force for a given task while protecting against overloading