Lens Flashcards
(177 cards)
1
Q
The Lens is specialized __epithelial/endothelial__ tissue that is responsible for fine-tuning the image that is projected on the __cornea/retina_____.
A
epithelial, retina
2
Q
T/F Intraocular lens can be compared to a camera lens.
A
T
3
Q
The lens must be transparent, have a higher refractive index than the medium in which it is suspended, and have refractive surfaces with the proper curvature to allow what to occur?
A
for the lens to fine-tune an image that is projected onto the retina
4
Q
T/F The curvature of surfaces must not be variable to permit the optical system to focus on objects that are far or near.
A
False, curvature of surfaces must be variable
5
Q
Disruption of the precise organization of the lens _fiber/protein__ cells or damage to the fiber/protein within them can destroy the _opaqueness/transparency__ of the lens, a process known as _cataract/pterygium__ formation.
A
fiber, proteins, transparency, cataract
6
Q
The lens is formed from __two/three populations of specialized epithelial cells.
A
two
- cuboidal cells
- elongated fiber cells
7
Q
On the anterior/posterior surface of the lens closest to the __cornea/iris__ is a sheet of __cuboidal/fiber__ cells, the lens epithelium.
A
anterior, cornea, cuboidal
8
Q
The bulk of the lens consists of elongated _cuboidal/fiber__ cells.
A
fiber
9
Q
T/F The lens capsule, an elastic extracellular matrix that surrounds the entire lens is secreted by the epithelial and superficial fiber cells.
A
True
10
Q
Most epithelial cells __do/do not__ divide.
A
DO NOT
11
Q
In the germanitive zone __near/away__ the equatorial margin of the lens epithelium/endothelium cells do/do not proliferate and do so slowly/quickly
A
near, epithelium, DO, slowly
12
Q
T/F The junctions between the apical and basal ends of cells from the opposite sides of the lens are called the common junction.
A
False, they are called sutures.
13
Q
Fiber cells __stop/start__ elongating when they reach the sutures and their basal ends __detach/attach__ from the capsule.
A
stop, detach
14
Q
Mature/Young fiber cells are gradually buried deeper in the lens as successive generations of fibers elongate/shorten and differentiate
A
mature, elongate
15
Q
Lens increases/decreases in size; synthesis ceases/continues just before organelle degradation.
A
increases, ceases
16
Q
The components of mature fiber cells in the lens, must be much less stable than those in cells found in other parts of the body.
A
False, much more stable
17
Q
The lens is suspended in the posterior/anterior of the eye by a band of inelastic/elastic microfibrils, the Zonules/Iris, which insert into the lens capsule near the equator.
A
anterior, inelastic, zonules
18
Q
The zonule fibrils originate in the pigmented/nonpigmented layer of the ciliary/corneal epithelium, a tissue that is located just posterior to the iris.
A
non-pigmented, ciliary
19
Q
T/F Changes in the tension applied to the zonules are responsible for the alterations in lens curvature during accommodation.
A
True
20
Q
The refractive properties of the lens are the result of the high/low concentration of crystallins in the cytoplasm/nucleus of the lens fiber cells/wing cells and the curvature of the lens surfaces.
A
high, cytoplasm, fiber cells
21
Q
Lens crystallins accumulate to concentrations that are ________higher than in typical cells.
a. 1x
b. 2x
c. 3x
d. 4x
A
c. 3x
22
Q
The lower/higher concentration of crystallins give lens fiber cells a significantly lower/higher refractive index than the fluids around the lens.
A
higher, higher
23
Q
T/F In younger individuals, refractive error is often caused by defects in the curvature or refractive index of the lens.
A
False, In younger individuals, refractive error is often caused by abnormalities in corneal curvature or the length of the globe, RARELY by defects in the curvature or refractive index of the lens.
24
Q
Transparency depends on maximizing/minimizing light scattering and absorption.
A
minimizing
25
Pick the best answer, may pick more than one answer.
Light passes smoothly through the lens as a result of:
1. the regular structure of lens fibers
2. the absence of membrane-bound organelles
3. the small and uniform extracellular space between the fiber cells.
All three statements are correct
1. the regular structure of lens fibers
2. the absence of membrane-bound organelles
3. the small and uniform extracellular space between the fiber cells.
26
In _young/older_ individuals, the human lens is nearly _colorful/colorless_.
young, colorless
27
The human lens absorbs _increasing/decreasing _ amounts of _short/long_ wavelengths as it ages.
increasing, short
28
T/F Pseudophakia is the absence of the natural crystalline lens, either from natural causes or because it has been removed.
False, Aphakia
29
T/F Aphakia is the substitution of the natural crystalline lens with a synthetic lens.
False, Pseudophakia
30
Pseudophakic IOLs are used in _cataract surgery/cornea surgery_.
Cataract surgery
31
Congenital aphakia can be caused by a _Hepatitis/Rubella_ infection in first _4/8/10_ weeks of pregnancy.
Rubella, 4
| can also be caused by a mutation in the PAX-6 gene
32
T/F Lens fiber differentiation depends on synthesis and accumulation of large amounts of crystallins.
True
33
As much as ____of the wet weight of the lens fiber cell can be accounted for by crystallins, a protein concentration that is approximately ___ higher than that in the cytoplasm of typical cells
a. 25%, 3x
b. 40%, 2x
c. 50%, 2x
d. 40%, 3x
d. 40%, 3x
34
Crystallins are classified into 2 categories:
1. Classical and Taxon-specific
2. Classical and Non-classical
3. Taxon-specific and Taxon-nonspecific
4. Type1 and Type 2
1. Classical and Taxon-specific
35
T/F All vertebrae lenses accumulate the Classical crystallins, which consist of α-crystallin family and β/γ-crystallin superfamily.
True
36
Taxon-specific crystallins are _functional/non-functional_ enzymes or proteins that are structurally _similar/dissimilar_ to enzymes but that _lack/contain_ enzymatic activity.
functional, similar, lack
37
T/F Adult human lenses DO produce taxon-specific crystallins,
False Adult human lenses DO NOT produce taxon-specific crystallins,
38
T/F The enzyme betaine-homocysteine methyltransferase is present at high levels in the embryonic nucleus, indicating that this enzyme serves as a taxon-specific crystallin during the early development of the human lens.
True because Adult human lenses DO NOT produce taxon-specific crystallins,
39
Human lenses express ___ α-crystallin genes.
a. 1
b. 2
c. 3
d. 4
b. 2, αA and αB.
40
The role of the α-crystallins in _promoting/preventing_ protein aggregation and precipitation has been demonstrated in experiments performed _in vivo/in vitro_.
preventing, in vitro
41
Analysis of αA knockout mice: protein aggregates show _large/small_ amounts of αB-crystallin and _larger/smaller_ amounts of other proteins.
Resulted in Lens _smaller/larger_ than normal-structurally similar though and formation of cataract in first _one/few_ weeks.
large, smaller
smaller, few
42
(αB-crystallin/αA-cryastallin) is present in a variety of cells throughout the body, especially in heart and skeletal muscle.
αB-crystallin
43
T/F In vitro tests showed that the mutant form of the protein αB-crystallin had chaperone activity and did not enhanced the aggregation of test proteins.
False, In vitro tests showed that the mutant form of the protein αB-crystallin had NO chaperone activity and even ENHANCED the aggregation of test proteins.
44
T/F Studies suggest that αB-crystallin has important chaperone functions in the lens and in other cells of the body.
True
45
The β/γ-crystallin superfamily is _less/more_ diverse than the α-crystallins, and the function of its members in the lens is _less/more_ evident.
more, less
46
___ β-crystallin polypeptides and ____ γ-crystallins are expressed in the human lens.
a. 3, 6
b. 3, 3
c. 6, 3
d. 6, 6
c. 6, 3
47
Classical crystallins have a composition of ____ water and ____ organic matter (of which ____ is structural proteins).
a. 35%, 65%, 33%
b. 33%, 35%, 65%
c. 65%, 35%, 33%
d. 65%, 33%, 35%
c. 65%, 35%, 33%
48
Microtubules are _abundant/sparse_ beneath the plasma membranes of lens fiber cells.
abundant
49
Microtubules play Important roles in:
1. stabilizing the fiber cell membrane
2. transporting vesicles to the apical and basal ends of elongating fiber cells
3. gives lens its birefringent property
4. all of the above
4. all of the above
50
The membranes of mature lens fiber cells have an _usual/unsusal_ lipid composition
unusual
51
Human lens fiber cells have the _lowest/highest_ proportion of _glucose/cholesterol and sphingomyelin of any plasma membrane in the body, and the amount of _glucose/cholesterol_ _increases/decreases_ as the fiber cells mature.
highest, cholesterol, cholesterol, increases
52
The cholesterol/phospholipid ratio is nearly ___ ___ greater in nuclear than in cortical fiber cells.
a. 2 fold
b. 3 fold
c. 4 fold
d. 5 fold
b. 3 fold
53
T/F The presence of high concentrations of cholesterol and sphingomyelin is likely to cause lens fiber cell membranes to be flexible.
False, cause lens fiber cell membranes to be rigid,
54
T/F The human lens grows rapidly in the embryo and during the first postnatal year
True
55
The rate of lens growth slows between ages ___ and ____years, then continues at a much slower, nearly linear rate throughout life.
a. 2 and 10
b. 1 and 5
c. 1 and 10
d. 2 and 5
c. 1 and 10
56
In the _anterior/posterior_ of the lens, this network, the tunica vasculosa lentis, arises from the _iris stroma/hyaloid artery_.
posterior, hyaloid artery
57
T/F The capillaries at the _anterior/posterior_ of the lens arise from blood vessels of the developing iris stroma to form the _anterior/posterior_ papillary membrane.
anterior, anterior
58
During the _____ trimester of human development, the capillaries of the tunica vasculosa lentis and the anterior papillary membrane regress.
a. first
b. second
c. third
b. second
59
Absence of the lens at an early stage of embryogenesis leads to
1. the absence of the corneal endothelium
2. abnormal differentiation of the corneal stroma
3. absence of the iris, ciliary body, and anterior chamber.
4. all of the above
4. all of the above
60
T/F The lens derives much of its energy from glycolysis.
True
61
The _start/end_ product of glycolysis is lactic acid.
end
62
As a result of lactate accumulation, intracellular pH _raises/drops_ significantly from _peripheral/central_ to deeper fiber cells.
drops, peripheral
63
T/F If cells could survive in an atmosphere free of oxygen, most oxidative damage could be avoided.
True
64
Molecular _oxygen/nitrogen_ is, directly or indirectly, the source of _least/most_ oxidative damage.
oxygen, most
65
The oxygen tension around the lens in the living eye is low, approximately ____ mm Hg
a. 10
b. 15
c. 20
d. 25
b. 15
66
The _low/high_ oxygen tension around and within the lens probably _damages/protects_ lens proteins and lipids from oxidative damage.
low, protects
67
Despite the _low/high_ oxygen level, the lens derives a substantial proportion of its ATP form _glycolysis/oxidative phosphorylation_- a process that generates free radicals.
low, oxidative phosphorylation
68
T/F The lens is not exposed to solar irradiation throughout its life.
False. it IS exposed
69
Much of the solar irradiation that reaches the eye is absorbed by the _cornea/retina_, but the remaining UV light _could have/could not have _ harmful effects on the lens
cornea, could have
70
T/F If light is not absorbed, it produces no damage.
true
71
T/F DNA, proteins, nucleoside-containing metabolites, flavonoids, and pigments all absorb UV light and thus are not potential sources of free radicals
False, DNA, proteins, nucleoside-containing metabolites, flavonoids, and pigments ARE all potential sources of free radicals.
72
T/F Glutathione a tripeptide of the amino acids glutamine, cysteine, and glycine, provides most of the protection against oxidative damage in the lens.
True
73
When glutathione levels have been _raised/lowered_ in lens epithelial cells or whole lenses, cell damage and cataract formation follow _rapidly/slowly_.
lowered, rapidly
74
T/F Ascorbic acid also provides protection to the lens from oxidative damage.
True
75
Ascorbic acid is _actively/passively_ transported from the blood to the aqueous humor by a Na-_dependent/independent_ transporter in the ciliary _epithelium/endothelium_.
actively, dependent, epithelium
76
Ascorbic acid reaches concentrations in the aqueous humor that are up to _____ higher than levels in the blood.
a. 5x
b. 15x
c. 20x
d. 50x
c. 20x
77
As a result of the _abundance/lack_ of blood supply, the oxygen concentration within and around the lens is much _lower/higher_ than that in most other parts of the body.
lack, lower
78
T/F The lens does not depend on glycolytic metabolism to produce much of the ATP and the reducing equivalents required for its metabolic activities
the lens DOES depend on glycolytic metabolism
79
The glucose required for glycolytic metabolism is derived from the _vitreous humor/aqueous humor_.
aqueous humor
80
T/F Aqueous humor glucose levels are maintained by facilitated diffusion across the ciliary epithelium.
True
81
T/F Lens epithelial and superficial fiber cells do not contain mitochondria.
False. Lens epithelial and superficial fiber cells also HAVE NUMEROUS mitochondria
82
Cells near the surface of the lens _may use/cannot use_ both glycolytic and oxidative pathways to derive energy from glucose.
may use
83
```
Lens should maintain:
_low/high_ K+,
_low/high_ Na+
_low/high_ Cl-
_low/high_ water
```
High K+,
low Na+
low Cl-
low water
84
If sodium moved into lens increases in solutes, water content will _increase/decrease_ (osmotically)
increase
85
In water electrolyte balance of the lens, the concentration gradient of aqueous has _more/less_ Na+, _low/high_ K+.
more Na+, low K+
86
The electrical gradient inside the lens is _electropositive/electronegative_.
electronegative
87
The water electrolyte balance is maintained by _________ pump.
1. Na+/Cl-
2. Na+/Na+
3. Cl-/K+
4. Na+/K+
4. Na+/K+
88
Sodium -Potassium pump operates in the lens _endothelium/epithelium_, which _has/does not have_ mitochondria
epithelium, has mitochondria
89
```
Sodium -Potassium pump requires energy and
___ Na+ removed ___K+ is allowed.
a. 2 Na+, 3 K+
b. 2 Na+, 2 K+
c. 3 Na+, 2 K+
d. 3 Na+, 3 K+
```
c. 3 Na+, 2 K+
90
The human lens is _opaque/transparent_ to most wavelengths of visible light, it produces and accumulates _chromophores/chromosomes_ that absorb the _shortest/longest_ wavelengths of the visible spectrum.
transparent, chromophores, shortest
91
At birth, the human lens is _____ to _______.
1. clear and pale pink
2. pink and pale yellow
3. clear and pale brown
4. clear and pale yellow
4. clear and pale yellow
92
T/F With increasing age, the amount of yellow pigmentation in the lens decreases.
T/F This pigmentation absorbs the shorter, more energetic wavelengths of light, preventing them from reaching the retina.
False. increases
True
93
With a _low/high_ concentration of the chromophores, they can _increase/reduce_ visual acuity by _increasing/decreasing_ light absorbance, leading to the formation of what is termed a brunescent or nigrescent cataract.
high concentration, reduce visual acuity, increasing light absorbance
94
Brunescent cataract is _less/more_ common in developing countries, which suggests that environmental or nutritional factors _may be/may not be_ important.
more, may be
95
T/F Pterygium is an opacification of the lens.
False, Cataract
96
T/F A clinically significant cataract interferes with visual function.
True
97
A cataract is a loss of lens transparency with increased light scattering caused by:
1. Disruption of lens fiber cell structure
2. Increased protein aggregation
3. Phase separation lens cell cytoplasm.
4. 1 and 2
5. 1 and 3
6. 1, 2 and 3
6. 1, 2 and 3
1. Disruption of lens fiber cell structure
2. Increased protein aggregation
3. Phase separation lens cell cytoplasm
98
T/F Cataract formation general effect is change in amount of soluble and insoluble lens protein.
True
99
Lens grows with age hence the protein content also _decreases/increases_ with age.
increases
100
T/F In cornea formation, the process of change of soluble to insoluble lens protein is by cross linking.
False, cataract formation
101
The most common types of age-related cataracts are:
1. nuclear
2. cortical
3. posterior subcapsular.
4. 1 and 2
5. 1, 2 and 3
5. 1, 2 and 3
1. nuclear
2. cortical
3. posterior subcapsular
102
Nuclear cataracts occur in the _youngest/oldest_ fiber cells, those formed during embryonic and fetal life.
oldest
103
Cortical cataracts occur in cells formed _earlier/later_ in life.
later
104
T/F Posterior subcapsular cataracts (PSCs) result from light scattering by a plaque of swollen cells at the posterior pole of the lens.
True
105
Abundant evidence shows that nuclear cataracts are associated with _increased/decreased_ oxidative damage to lens proteins and lipids.
increased
106
Nuclear cataracts are age-dependent and are _more/less_ susceptible to oxidative damage.
more
107
T/F Any decrease in oxidative load or further decrease in the ability of the lens nucleus to cope with the normal level of oxidation is likely to lead to nuclear cataract formation.
False. increase in oxidative load
108
T/F Studies show association between oxidation, age, and cataract formation was provided by studies of patients treated with hyperbaric oxygen to alleviate the complications of peripheral vascular disease.
True
109
These individuals were exposed to ____ to ____ atmospheres of pure oxygen for ___ hour each day for up to 3 years. Of the 25 patients treated in this study, all but one had increased light scatter in the lens nucleus and seven developed frank nuclear cataracts.
a. 1.0 to 1.5, 1 hour
b. 2.0 to 2.5, 1 hour
c. 3.0 to 3.5, 2, hours
d. 2.0 to 2.5, 2 hours
b. 2.0 to 2.5, 1 hour
110
T/F The onset of nuclear cataract formation is often associated with an increase in the refractive power of the lens.
True
111
T/F For patients with myopia, this myopic shift temporarily causes an improvement in their near visual acuity, a phenomenon often called second sight.
False, for patients with hyperopia
112
Patients treated with hyperbaric oxygen also experienced significant _hyperopic/myopic_ shift, like that seen just before the formation of a nuclear sclerotic cataract.
myopic shift
113
Nuclear cataracts commonly occur in _younger/older_ patients within 6 months to 3 years after vitrectomy.
older
114
Anterior vitreous oxygen tension: _low/high_
| Posterior vitreous oxygen tension: _low/high_
Anterior vitreous oxygen tension: LOW
| Posterior vitreous oxygen tension: HIGH
115
With a removed vitreous the lens is exposed to _decreased/increased_ oxygen which can lead to oxidative stress.
increased
116
T/F The high incidence of nuclear cataracts after this procedure is probably a result of changes in the environment around the lens, rather than a direct effect of the procedure on the lens.
True
117
```
The oxygen tension in the anterior vitreous is normally low, approximately ____ mm Hg.
a 14
b.15
c,16
d.17
```
c. 16
118
The oxygen tension in the posterior vitreous near the retinal vessels is _low/high_, decreasing in a sharp gradient within the first _1/3/5_ mm of the vitreous body.
high, 1
119
_It is not/It is_ possible that when the vitreous is removed and the fluid in the eye can circulate freely the lens is exposed to _decreased/increased_ oxygen from the retina.
It IS possible, increased
120
T/F Changes in protein organization leading to cataract are not subtle.
False, are subtle
121
In cataract formation, a _small/large_ change in protein aggregation leads to a large amount of light scattering.
small
This makes it difficult to identify the changes that lead to opacification among the many alterations of lens proteins that occur with aging.
122
T/F The lens fiber cell are still well organized and intact despite a cataract is formed.
True
123
T/F In the senile cataract hypothesis, the higher molecular fractions do not grow in the cell cytoplasm.
False. HM fractions DO grow in to the cell cytoplasm.
124
In the ssenile cataract hypothesis, growing HM aggregates may cause the cell membrane to _rupture/generate_ causing cellular debries.
rupture.
The HM fractions pull and break cytoplasm. This leads to fragmenting of cells. These fragments may become like debris and scatter light.
125
Cortical cataracts occur in the _young/mature_ fiber cells lying close to the lens surface.
mature
126
Cortical cataracts most often occur in the _superior/inferior_ half of the lens, with a tendency for these cataracts to occur in the _superior/inferior_ nasal quadrant.
inferior, inferior
127
T/F Examination of the affected regions of lens fiber cells in a cortical cataract reveals almost complete disruption of cell structure.
True
128
Early-stage cortical cataracts usually _are/are not_ clinically significant because the opacity is limited to the lens _center/periphery_ and does not impinge on the visual axis.
are not, periphery
129
T/F As the cortical cataract progresses, the peripheral opacity may spread toward the visual axis, eventually interfering with vision. .
True
| However, an individual may have a cortical opacity for years without experiencing a diminution of visual function
130
Extension of the opacity along the lengths of a small cluster of fiber cells leads to the formation of the “cortical spokes” that are often described in what type of cataracts?
Cortical cataract
131
Posterior subcapsular cataracts (PSC) are caused by light scattering in a cluster of swollen cells at the _anterior/posterior_ pole of the lens, just _beneath/above_ the capsule.
posterior, beneath
132
PSCs are particularly disabling. why?
Because the opacity produced by these cells is in the optical axis..
133
PSCs result from the _normal/abnormal_ migration of lens epithelial cells or the aberrant differentiation of lens _wing/fiber_ cells.
abnormal, fiber
134
“Pure” PSCs typically account for less than ___ of cataracts in humans. However, PSCs commonly occur in conjunction with _____ or _______ opacities.
a. 10%, nuclear, cortical
b. 20% nuclear, cortical
c. 10% nuclear, congenital
d. 20% traumatic, cortical
a. 10%, nuclear, cortical
135
T/F PSC cataracts affect near vision more when compared to distance vision in theory.
True
136
Patients with cataracts often have a combination of what type of cataracts?
a. nuclear and cortical
b. nuclear and posterior subcapsular
c. posterior subcapsular and cortical
d. nuclear, cortical and/or subcapsular
d. nuclear, cortical and/or subcapsular
137
In _less/more_ developed countries, cataracts are removed as soon as they become visually disabling.
more
138
T/F If a cataract is removed, it may progress to a total or “morgagnian” cataract.
False, if cataract NOT removed
139
Is there a specific cause for total cataracts?
There is NO specific cause for total cataracts.
They are simply the result of the progression of a more localized cataract to the point at which it affects the entire lens.
140
T/F The most common approach taken to remove cataracts in developed countries is to
- remove a portion of the anterior lens epithelium
- capsule to expose the underlying fiber mass;
- extract the nuclear and cortical fiber cells, often using instruments for “photoemulsification”;
- implant a plastic intraocular lens (IOL) in the capsular bag.
True
141
T/F The phacoemulsification method of cataract removal is a form of intracapsular cataract extraction.
False. extracapsular cataract extraction
142
What is a common complication of extracapsular cataract extraction?
1. formation of secondary cataracts
2. formation of nuclear cataract
3. none
1. formation of secondary cataracts also called after cataracts or posterior capsular opacification (PCO).
143
T/F Before IOLs were available, the entire lens was removed to remove the cataract.
True, this method is known as Intracapuslar Cataract Extraction:
144
What is/are true statements about intracapsular cataract extraction?
1. more common in developing countries
2. Rare in most places-
3. Older technique
4. entire lens is removed to remove cataract
5. all of the above
5. ALL OF THE ABOVE
1. more common in developing countries
2. Rare in most places-
3. Older technique
4. entire lens is removed to remove cataract
5. all of the above
145
Lens epithelial cells _near/away from_ the lens equator persist after cataract surgery and can migrate _beneath/above_ the IOL onto the denuded posterior capsule.
near, beneath
146
T/F If the epithelial cells migrate further onto the posterior capsule, they may differentiate into small “lentoid bodies”, also called Elschnig’s pearls.
True
147
Congenital cataracts are cataracts that are present at?
1. death
2. after a traumatic injury
3. birth or appear soon after birth.
3. birth or appear soon after birth
148
T/F One infectious cause of congenital cataracts is rubella infection in early pregnancy.
True
The rubella virus has been isolated from the lenses of affected individuals, and experimental infection of early-stage human lens tissue with the rubella virus has been demonstrated.
149
Anterior Polar Cataracts is another _early/late_-onset cataract and is an opaque plaque is formed near the _periphery/center_ of the lens epithelium.
early, center
150
Which of the following are hereditary syndromes with associated cataract formation? (more than 1 answer is correct)
1. Oculocerebrorenal syndrome of Lowe
2. Neurofibromatosis type 2
3. Hyperferritinemia
4. Werner syndrome
5. Myotonic dystrophy
6. Galactokinase deficiency and galactosemia
7. Fabrys disease
8. none of the above
9. all of the above, except for #8
9. all of the above, except for #8
1. Oculocerebrorenal syndrome of Lowe
2. Neurofibromatosis type 2
3. Hyperferritinemia
4. Werner syndrome
5. Myotonic dystrophy
6. Galactokinase deficiency and galactosemia
7. Fabrys disease
151
T/F In galactosemia and galactokinase deficiency, sugar or galactose accumulates to low levels in the body.
False accumulates to HIGH levels in the body.
152
In the Diabetic and Galactosemic cataract, the following statements are true except:
1 Conversion of glucose or galactose to respective sugar alcohols occurs via sorbitol pathway.
2. Sorbitol cannot readily diffuse out of intracellular compartment.
3. Osmotic gradient favors influx of H2O
4. process is exclusive to women
5. Sugar alcohols and sugar itself will lead to protein aggregation
4. process is exclusive to women.
pathways can occur in both men and wowen
153
T/F Studies show a high lifetime exposure to UV light has not been linked to the formation of cataracts.
False HAS BEEN LINKED
Epidemiologic studies have linked high lifetime exposure to UV light with the formation of cortical cataracts in humans
154
T/F The mechanism by which UV exposure leads to cataract formation in humans has not been identified.
True
155
Although these studies have suggested that UV-generated free radicals can _damage/repair_ components of the lens in a similar manner to that seen in cataract formation, these studies often _do not/do_ fully take into account the biology of the human lens.
damage,do not
156
T/F Long-term exposure to infrared light and focused,high-energy microwaves can also cause cataracts.
True
Evidence that infrared light can cause cataracts comes mostly from epidemiologic studies in individuals exposed as a result of their occupation. This type of cataract is also called glass-blowers cataract.
157
T/F Glass-blowers cataract is congenital.
False.
| Cataract formed after exposure due to their occupation, not born with
158
Long-term exposure to _low/high_-dose steroids is a significant risk factor of PSC formation in humans.
High
159
T/F Increased intracellular calcium can induce formation of cataracts.
```
True.
Increased intracellular calcium affects
-glucose metabolism,
-inhibition of protein synthesis,
-induction of HM aggregates
-direct loss of transparency
-Inhibit sodium pump
```
160
T/F Hypocalcemia is related to the dependency of the membrane permeability to levels of calcium and marked electrolyte and water imbalance in low calcium environment.
True
161
People with diabetes are at _decreased/increased_ risk for early-onset cataracts.
increased
162
The lens provides a _useful/useless_ system with which to study diabetic complications.
useful
163
Damage to the lens seems to be entirely a result of the _low/high_ glucose level in diabetic patients.
high
164
In the Diabetes and lens osmotic hypothesis the following is the sequence of events leading to cataract formation:
1) Lens toxic levels of glucose
2) Aldose reductase activated
3) Glucose converted to sorbitol
4) Sorbitol cannot escape the lens now
5) Polyol dehydrogenase tries to get rid of sorbitol be converting it to fructose (reaction slow)
6) High intracellular osmotic pressure
7) Cells burst debris becomes manifestation of cataract
Know that people with diabetes are at _decreased/increased_ risk for early-onset cataracts
Osmotic hypothesis has good experimental support in formation of cataract due to diabetes
165
T/F Osmotic hypothesis has good experimental support in formation of cataract due to diabetes
True
166
T/F Cataract formation due to denaturing of proteins due to glycation and oxidative stress is a supported theory.
False not a well supported theory
167
What is the primary risk factor for the most common kinds of cataract?
Age
168
One risk factor common to most kinds of cataracts is _lower/higher_ socioeconomic status or _higher/lower_ education level.
lower, lower
169
_Lower/Higher_ socioeconomic status may predispose patients to nutritional deficiencies, increased exposure to diseases, poor general health status, and increased occupation exposure to cataractogenic agents.
Lower
170
T/F Women are at decreased risk for most kinds of cataract.
False, increased
171
Smoking and _low/high_ alcohol consumption have been identified in several studies as dose-dependent/dose-independent_ risk factors for nuclear and in some cases cortical cataracts.
high alcohol, dose-dependent
172
Dark iris color is associated with _lower/higher_ incidence of all types of lens opacities.
higher
173
Dark Iris color may also be related to _lower/higher_ levels of cortical cataract in African-Americans than in Caucasians.
higher
174
T/F Studying the genetics of cataracts will provide information about the cataract formation.
True
175
Moderate caloric restriction, which _reduces/increases_ cataract incidence and _slows/speeds_ cataract progression in animals, also _slows/speeds_ or prevents a variety of other age-related conditions.
reduces, slows, slows,
176
T/F Numerous epidemiologic studies suggest that nutrition does not play an important role in cataract formation.
DOES play an important role
177
T/F Information from the Age-Related Eye Disease Study may provide useful guidelines for the effects of a few components of the diet on cataract formation.
True
Age-Related Eye Disease Study is a large-scale clinical trial of the effects of selected vitamin and nutrient supplementation on the progression of eye diseases.
