The Optics of the Eye Flashcards
What is accommodation of the eye?
When your eye focuses the lens system in the eye.
What does accommodation of the eye involve?
the change in the shape of the lens.
Why does accommodation of the eye occur?
In order to see close objects.
What does it mean when lens become taut?
The lens flattens and its refractive power decreases.
What occurs when in accommodating for distant vision?
Ciliary muscles relax and the zonule of Zinn becomes taut.
What occurs when accommodating for near vision?
ciliary muscles contract and Zonule fibers relax.
What occurs when Zonule fibers relax?
it causes the lens curvature to increases > leading to refractive power increasing.
Parasympathetic activation stimulates the contraction of what causing what?
of the ciliary muscles causing the relaxation of the Zonule of Zinn.
When lens become more convex and increases its refractive power what just occurred?
The Zonule of Zinn is relaxed.
What is presbyopia?
The inability of the lens to change its shape during accommodation.
What reduces with age?
The capability or power of accommodation.
Why does the capability of accommodation reduce with age?
lens become thicker, larger, and less elastic due to denaturation of lens proteins.
In children the refractive power of the lens can do what?
increase voluntarily by 14 diopters.
By age 45-50 the accommodation capabilities do what and by how much?
Reduce from 14 to 2 diopters.
A middle aged person has a refractive lens power of what?
2 diopters.
By age 70 accommodation capabilities is what?
0
Eyes are permanently focused at a constant distance at what age and what do they need?
age 70 and they need bifocals.
What is the function of the iris?
The iris regulates the amount of light entering the eye.
What occurs in darkness what happens to the iris?
more light enters.
What occurs in a bright environment to the iris?
the less light enters the eye.
What are pigmented in the iris?
The stroma and epithelial cells.
What forms the boundary of the pupil?
The medial or inner aspect of the iris.
Define the pupillary zone?
The medial or inner aspect of the iris forms the boundary of the pupil.
The lateral or outer segment of the iris is attached to the what?
The ciliary body and sclera.
What does the pupillary region contain?
The sphincter muscles of the iris.
What does the ciliary region contain?
The radial muscles of the iris.
What is the sphincter muscle also known as?
pupillary sphincter, pupillary constrictor, or circular muscle of iris.
What is the radial muscle of the iris is also known as?
pupil dilator muscle or pupillary dilator.
What type of muscles are the sphincter and radial muscles?
Smooth muscles that regulate the size of the pupil.
What is the area called between the pupillary and ciliary zones of the iris known as?
Collarette region of the iris.
The amount of light entering the eye is proportional to what?
The area of the pupil.
The human pupil can become as narrow or as wide as what?
1.5 mm or as wide as 8mm
When pupil is narrowing or widening the amount of light entering the eye can change by how much?
30 folds due to the changes in pupillary diameter.
What muscle exhibits the parasympathetic effect?
The sphincter muscles
What muscle exhibits the sympathetic effect?
radial muscles of the iris.
What two muscles regulate the pupillary diameter?
the radial and sphincter muscles.
What occurs to pupillary diameter in low light?
the radial muscles contract while the sphincter muscles relax to widen pupil.
What occurs to the pupil when the radial muscles contract while the sphincter muscles relax?
the pupil will widen.
What occurs to pupillary diameter in high light?
The radial muscles will rely while sphincter muscles contract to narrow pupil.
What occurs to the pupil when radial muscles relax and sphincter contracts?
the pupil will become narrow.
What is emmetropia?
Normal vision
What is hyperopia?
farsightedness
What is hyperopia also known as?
hypermetropia
In hyperopia, light is focused behind the retina this error is caused primarily by what?
a short eye ball.
In hyperopia, light is focused behind the retina this error is caused secondarily by what?
by a lens with weak refractive power.
In hyperopia the light rays aren’t bent sufficiently by a weak lens this is why?
light rays are focused behind the retina of a short eye ball.
When hyperopia’s error occurs, who compensates it?
accommodation will try to wherever its possible.
In older subjects why isn’t accommodation can’t compensate hyperopia?
they are presbyopic subjects. Lenses can’t accommodate.
In myopia where is light focused on?
In front of the retina.
What is myopia is also known as?
nearsightedness.
What causes the error of myopia?
usually caused by a long eye ball o by lens with too much refractive power.
In myopia light rays are bent strongly resulting in what?
focusing light infront of the retina of a long eyeball.
Which condition of the eye cannot compensate for the action of the lens?
Myopia
Which condition of the eye can compensate for the action of the lens?
Hyperopia
What kind of lenses used to correct myopia?
concave lenses
Why are concave lenses used to correct myopia?
they disperse light entering the eye.
What kind of lenses are used to correct hyperopia?
Convex lenses
Why are convex lenses used to correct hyperopia?
They converge light entering the eye.
What is astigmatism?
an optical defect caused by refractive error due to eye unable to focus.
In astigmatism what occurs to images in planes that are right angles to each other?
focused at different distances cause the image to be blurred with lack of fine detail.
Where are the focal points of the astigmatic eye?
focal points are in different planes.
What causes astigmatism?
differences in the degrees of curvature of the cornea and of the lens.
Astigmatism is usually do to what?
too great a curvature of the cornea.
How can astigmatism be corrected?
cylindrical lens with different radii of curvature in different planes.
What is visual acuity?
clearness of vision.
How is visual acuity determined by?
the sharpness of focus of image on retina and the sensitivity of brain interpretative system.
How is visual acuity assessed?
the ability to recognize different sizes of letters or symbols at a standard distance.
The visual acuity symbolizes what?
The smallest details the eye can see
What does visual acuity not measure?
the total quality of vision.
What chart is used to measure visual acuity?
The Snellen Eye Chart.
Predator animas have eyes in the front of their head meaning what?
The are primarily binocular vision.
What is binocular vision necessary for?
perception of depth.
