Vision & Optical Instruments Flashcards
What anatomical feature of the eye has the greatest density of light receptors and the greatest acuity (sharpness) in the visual field?
The fovea
What does the cornea and lens do as a unit?
Form a system that acts as a single thin lens.
A real image must be projected onto the light sensitive ______, which lies at a fixed distance from the lens.
Retina
What allows the eye to detect light intensities from the lowest observable to 10^10 times greater (without damage)?
The variable opening (pupil) of the eye along with chemical adaptation.
Which nerve conveys signals received by the eye to the brain?
The optic nerve.
Where does the biggest change in the refractive index, and bending of rays, occur in the eye?
The cornea, rather than the lens.
The image formed in the eye is much like what kind of lens?
A single convex lens.
The image must fall precisely on the retina to produce clear vision. How else might we might phrase this using physics terms?
The image distance, di, must equal the lens-to-retina distance
Because the lens-to-retina distance does not change, what must happen for the image distance, di, to accommodate for objects at various distances?
The image distance, di, must be the same for objects at all distance.
The eye manages this by varying the focal length of the lens to accommodate for objects at various distances.
The process of adjusting the eye’s focal length is called?
Accommodation
Light rays from a nearby object can diverge and still enter the eye. How must the lens accommodate this?
The lens must be more converging (more powerful) for close vision. To be more converging, the lens is made thicker by the action of the ciliary muscles.
When is the eye most relaxed?
When viewing distant objects.
Vision of very distance objects is called? While close vision is termed?
Totally relaxed
Accommodated
What is the thin lens equation?
P = 1/do + 1/di
What is the magnification equation?
m = -di/do = hi/ho
Define nearsightedness or myopia.
The inability to see distance objects clearly while close objects are clear.
Why does nearsightedness occur?
The eye over-converges the nearly parallel rays from a distance object and the rays cross in front of the retina.
The distance to the farthest object than can be clearly seen is called?
The far point of the eye (normally infinity).
Define farsightedness or hyperopia.
The inability to see close objects clearly while distant objects may be clear.
Why does farsightedness occur?
A farsighted eye does not converge sufficient rays from a close objec to make the rays meet on the retina.
The distance to the closest object that can be seen clearly is called?
The near point of the eye.
How do we correct nearsightedness?
Place a diverging spectacle lens in front of the eye. This reduces the power of the eye.
How do we correct farsightedness?
Plac ea converging spectacle lens in front of the eye. This increase the power of an eye that is too weak.
What is astigmatism?
An unevenness or asymmetry in the focus of the eye. This is mostly due to irregularities in the shape of the cornea.
