Visual Optics Flashcards
What is the focal length?
Distance behind a convex lens at which parallel light rays converge
How does distance of an object affect focal length?
If the light source is brought closer to the lens, the focal length increases
What is a diopter?
The refractive power of a lens
The inverse of the focal length
The bigger the number, the stronger the lens
What are the four refractive interfaces of the eye?
Cornea
Aqueous humor
Lens
Vitreous humor
What is the primary function of the lens in eye function?
Accommodation
Who has the full range of accommodation?
Only young children
What is presbyopia?
The decline in ability to accommodate.
The elasticity of the lens decreases with age
What does pupil diameter affect?
Depth of focus
What is depth of focus (field)?
The degree to which objects in front of, or behind, the point of visual fixation remain in focus
Greatest when pupil diameter is smallest
What is the near reflex?
A triad of reflexes that occur when the eyes are fixated on an object and that object is moved closer.
What are the three reflexes part of the near triad?
Convergence of eyes - centers object on fovea
Accommodation - focuses object
Miosis (Pupil constriction) - maximizes DoF
What is the Argyll Robertson pupil?
Refers to bilateral small pupils that constrict when a patient focuses on a near object, but do not constrict when exposed to bright light.
Strongly associated with neurosyphilis
How is pupil dilation and constriction controlled?
Parasympathetic regulation of the ciliary muscles
Increased parasympathetic firing to constrict the pupil, decreased firing to dilate
What is an emmetropic eye?
A normal eye
Considered to be normal when parallel rays of light from distant objects are in sharp focus on the retina when the ciliary muscle is completely relaxed
What is hyperopia?
Farsightedness
Caused by an eyeball that is too short, or occasionally a lens system that is too weak
What is myopia?
Nearsightedness
Caused by an eyeball that is too long, or occasionally by a lens system that is too strong
What is the correction for hyperopia?
Convex lens to add strength to the lens system
What is the correction for myopia?
Concave lens to decrease the strength of the lens system
What is astigmatism?
Refractive error in which light from different planes focus at different lengths.
Can be caused by uneven curvature of the cornea or lens
What is the correction for astigmatism?
A cylindrical lens having an appropriate axis and strength
What is keratoconus?
A progressive thinning and bulging of the cornea that distorts vision due to altered refraction
What is the correction for keratoconus?
An appropriately shaped contact lens
What is a cataract and how is it corrected?
Cloudy or opaque area in the lens that causes serious vision impairment
Surgical replacement of the lens is required
What is the consequence to visual acuity of the imperfection of the lens system in the eye?
Light from a point source spreads out over a circular spot on the retina
This spot is is brightest at the center and fades towards the edge.
Where is visual acuity the greatest?
At the fovea
What is the function of and difference between the aqueous and vitreous humor?
Functions to create pressure and maintain proper eye shape
Aqueous is a free flowing liquid
Vitreous is gelatinous, composed primarily of elongated proteoglycans
Where is aqueous humor produced?
Ciliary processes that extend from the ciliary body
What is normal intraocular pressure and how is it maintained?
15 mmHg
Determined by resistance to outflow of AH through the canal of Schlemm
What is Glaucoma?
A group of diseases which cause vision loss by damaging the optic nerve, which consists of axons of retinal ganglion cells
What are two ways that pharmacological treatments can be used to treat glaucoma?
Increase the rate of fluid outflow
Decrease the rate of formation of intraocular fluid
What are four tests used to detect glaucoma?
Tonometry - measurement of intraocular pressure
Ophthalmoscopy - visual inspection of the optic nerve head, or optic disk
Visual field testing - assessment of vision loss in specific areas
Gonioscopy - measurement of the angle betwen the iris and cornea
What open-angle glaucoma?
The angle between the iris and the cornea is large and intraocular fluid can flow to the trabecular meshwork, but it is partially blocked
More common, and associated with slow increase in intraocular pressure
What is closed-angle glaucoma?
The iris-cornea angle is closed, impeding outflow of fluid
Causes a rapid-rise in intraocular pressure and requires immediate medical treatment
