Week 2 - Exam prep Flashcards
What is the recommended approach to avoid symptoms of presbyopia for near add addition?
A) Employ the entire subjective amplitude of accommodation
B) Reserve one-third of the total subjective amplitude of accommodation
C) Reserve half of the total subjective amplitude of accommodation
D) Don’t reserve any subjective amplitude of accommodation
Reserve half of the total subjective amplitude of accommodation
To avoid symptoms of presbyopia, it is recommended to reserve half of the total subjective amplitude of accommodation. This means only a fraction of the accommodation amplitude should be employed while the rest should be prescribed as near addition.
If the task is at 33 cm and the subjective amplitude is 5.0 D, what would be the required near addition?
A) 3.5 D
B) 0.5 D
C) 1.5 D
D) 4.5 D
0.5 D
Accommodation demand = 1/ (distance of task in metres) == 1/0.33 = 3.0D
Half of the amplitude should be kept in reserve which is 5/2 = 2.5D.
So, the near addition required would be the difference between the accommodation demand and the reserved amplitude, which is (3.0 D - 2.5 D) = 0.5D. Therefore, the required near addition is 0.5D.
Why do corrected hyperopes need near addition earlier than corrected myopes, as stated in the slide?
A) Hyperopes have a greater accommodation amplitude
B) Hyperopes have a smaller accommodation amplitude
C) Myopes have a greater accommodation amplitude
D) Myopes have a smaller accommodation amplitude
Hyperopes have a smaller accommodation amplitude
Corrected hyperopes, individuals who are farsighted, have a smaller accommodation amplitude compared to corrected myopes, individuals who are nearsighted. Therefore, they require near addition earlier to compensate for the diminishing ability to accommodate for near vision tasks associated with presbyopia.
What is NRA and PRA and what does adding +/-0.25 result in?
NRA: negative relative accommodation
adding plus lenses will RELAX accommodation
PRA: positive relative accommodation
adding minus lenses will STIMULATE accommodation
e.g.
patient’s tentative add is 1.00D
NRA: +0.25 until sustained blur is reported is +1.0D
PRA: adding -0.25 until sustained blur is reported is -0.50D
Finally you need to adjust the NRA/PRA (aiming to have +/-0.75)
Therefore, final Near add = +1.25 D
This method OVERESTIMATES near addition
In the Binocular Cross method, what do you aim for and what do you if the vertical lines are clearer?
You should aim for equal clarity in both the horizontal and vertical lines.
If the vertical lines are clearer you add minus.
This methods tends to underestimate near add addition
How do you measure near add using the amplitude of accommodation?
Tentative near addition = working distance (D) – 1/2 Amplitude of accommodation (D)
* e.g.: if task at 50 cm (accommodation demand of 2.0 D), if the subjective amplitude is 3.0 D,
half the amplitude (1.5 D) is kept in reserve, therefore, a 0.5 D addition will be required.
* This method has been found to over-correct presbyopia (higher near addition)
A patient with initial tentative addition of +2.50 SD has NRA of +0.75 and PRA of -
1.25 DS. What could be the final addition?
NRA = +0.75
PRA = -1.25
Tentative is +2.50
Most plus = 2.50 + 0.75 = 3.25
Most minus = 2.50 - 1.25 = 1.25
3.25 - 1.25 = 2D, therefore should aim for +/-1.00 D
Final add = (1.25 + 1.00 = 2.25 or you can 3.25 - 1.00 = 2.25)
Which of the following statements about the lens epithelium is true?
A) Lens epithelial cells are primarily located on the posterior surface of the lens.
B) Lens epithelial cells lack gap junctions, leading to decreased lens transparency.
C) Lens epithelial cells are primarily composed of squamous cells.
D) Lens epithelial cells have gap junctions between cells to maintain lens transparency.
Lens Epithelial cells have gap junctions between cells to maintain lens transparency.
Lens epithelial cells are responsible for the growth and development of the entire lens. They are simple cuboidal cells that become columnar near the equator. These cells are restricted to the anterior surface of the lens, with their basal aspect in contact with the lens capsule. Lens epithelial cells contain a nucleus and organelles. Importantly, they have gap junctions between cells, which play a crucial role in maintaining lens transparency.
Which region of the lens epithelium is responsible for cell division through mitosis?
A) Central Zone
B) Germinative Zone
C) Transition Zone
D) Secondary Fibre Zone
Germinative zone
The lens epithelium consists of three main regions: the Central Zone, the Germinative Zone, and the Transition Zone. The Germinative Zone is the region where cells actively undergo mitosis or cell division. In this zone, new cells are continuously produced to contribute to the growth and maintenance of the lens.
What mechanism is primarily responsible for lens hydration?
A) Simple diffusion
B) Active transport of K+ and amino acids
C) Passive transport through epithelial barriers
D) Pump-leak system
Pump-leak system
Lens hydration, essential for maintaining transparency, primarily occurs via a “pump-leak” system. In this system, ions, solutes, and water move in and out of the lens through various mechanisms. Posteriorly, where there is no epithelial barrier, the permeable capsule allows free diffusion of ions, solutes, and water between the lens and vitreous. Anteriorly, active transport of K+ and amino acids into the lens occurs, which helps maintain an osmotic balance of lens hydration at the required level for transparency.
Which of the following statements about crystallin proteins in the lens is correct?
A) β-crystallin is the least abundant lens protein and serves as a chaperone preventing protein aggregation.
B) α-crystallin is the most abundant lens protein and is responsible for stress resistance.
C) γ-crystallin is specific to the lens and acts as a chaperone to prevent protein aggregation.
D) α-crystallin is a major lens protein and functions as a chaperone to prevent protein aggregation, with αA being specific to the lens and αB belonging to the heat-shock protein family.
D) α-crystallin is a major lens protein and functions as a chaperone to prevent protein aggregation, with αA being specific to the lens and αB belonging to the heat-shock protein family.
α-crystallin is indeed a major lens protein, constituting approximately 35% of the total protein content in the lens. It acts as a chaperone, preventing the aggregation of other lens proteins to maintain transparency and prevent cataract formation. αA-crystallin is specific to the lens and plays a crucial role in this chaperone function. αB-crystallin is also a member of the heat-shock protein family, contributing to stress resistance within the lens. β-crystallin is the most abundant lens crystallin, constituting approximately 54% of total lens protein, but its exact role is not entirely clear. Similarly, γ-crystallin is the least abundant lens crystallin, comprising only about 2% of total lens protein, and its specific role remains unclear as well.
Define presbyopia and explain the changes in accommodation with
age
- Loss of lens flexibility
- Reduced ciliary muscle strength
- Stiffening of zonules
Which theory of accommodation assumes that increasing tension during accommodation is exerted exclusively by equatorial zonules?
A) Helmholtz Theory
B) Schachar Theory
C) Hering’s Theory
D) Young-Helmholtz Theory
Schachars Theory
The Schachar Theory proposes that during accommodation, increasing tension is exerted exclusively by equatorial zonules. This theory suggests that the equatorial zonules play a significant role in the mechanism of accommodation. However, it has faced criticism due to concerns regarding the relatively small number of equatorial zonules and their ability to independently exert the necessary tension for accommodation.
Which type of lens zonules adhere to the valleys between ciliary processes?
A) Anterior zonules
B) Equatorial zonules
C) Posterior zonules
D) Medial zonules
Anterior zonules
The anterior zonules adhere to the valleys between ciliary processes. These zonules are responsible for supporting the anterior portion of the lens and play a crucial role in maintaining its position within the eye.
Which term refers to the residual accommodation present in the eyes at rest?
A) Dynamic accommodation
B) Tonic accommodation
C) Accommodative lag
D) Accommodative lead
Tonic accommodation
Tonic accommodation refers to the residual accommodation present in the eyes even when they are at rest, typically ranging from 0.5 to 1.5 diopters. This baseline level of accommodation enables the eyes to focus on distant objects without any external stimulus.
