Term
| Where does visual transduction occur? |
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Definition
| Visual transduction occurs in the retina |
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Term
| Where does the processing of visual information begin? |
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Definition
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Term
| What is the refraction and how can it be calculated? |
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Definition
Refraction is the bending of light and is caused by the change in velocity as the light is involved with interference as it passes from one substance to another.
-Refractive index can be calculated by
velocity of light in air/velocity of light in substance |
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Term
| T/F. The direction in which light travels is always parallel to the plane of the wave front. |
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Definition
| False. The direction in which light travels is always perpendicular to the plane of the wave front. |
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Term
| Describe the path light will travel when it strikes an interference with a higher refractive index perpendicular to the beam of light. |
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Definition
| The light continues on the same path however the velocity decreases and the wavelength shortens. |
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Term
| Describe the path light will travel when it strikes an interference with a higher refractive index at an oblique angle. |
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Definition
| The first portion of the wave which enters travels at a slower velocity, while the remainder of the wave continues ahead at the faster velocity. Consequently as a light wave passes completely through the interface, the wave gets turned at an angle, redirecting the path of the light beam. |
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Term
| When light strikes a substance with a different refractive index what determines the how the light will bend? |
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Definition
-the angle of incidence
-the ratio of the refractive indices |
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Term
| Describe the path of light passing through a convex lens? |
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Definition
| A convex lens causes light waves to converge on a focal point |
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Term
| Describe the path of light passing through a convex lens. |
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Definition
| A concave lens causes light waves to diverge |
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Term
| Describe the path of light waves that pass exactly through the center of a (A) convex lens and (B) a concave lens. |
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Definition
| Light waves passing directly through the center of either of these lenses would continue on a straight path. |
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Term
| Describe how a cylindrical convex lens will will bend light. |
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Definition
| Will bend light only in one plane so it will be focused on a line, instead of a point. |
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Term
| Describe how light passing through two perpendicular cylindrical convex lens will bend. |
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Definition
| The light act as if passing through a convex lens, forming a focal point. |
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Term
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Definition
| Focal length is the distance behind a convex lens at which parallel light rays converge |
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Term
| Will light have a longer focal length if it enters a convex lens from a near or more distant point? |
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Definition
| Light rays from source closer to the lens will have a greater focal length because the light rays enter as diverging rays. Light rays from a distant source enter as nearly parallel rays so they converge after a shorter distance. |
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Term
| What effect will increasing the convexity of a lens have on the focal length? |
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Definition
| Increasing the convexity of the lens will decrease the focal length. |
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Term
| What are two things you can change to decrease the focal length of light passing through a convex lens? |
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Definition
-Increase the convexity of the lens
-Increase the distance between the light source and the lens |
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Term
| When light passes through a convex lens the rays bend and are brought into focus at a point on the opposite side of the lens, what does this do to the image? |
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Definition
| The image is upside down, with respect to the original, and reversed from left to right. |
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Term
| How is the refractive power of a lens measured? |
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Definition
In diopters.
diopter = 1m/focal length (m) |
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Term
| What is the diopter of a lens that converges parallel rays of light on a focal point 10 cm from the lens? |
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Definition
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Term
| How is the dioptic strength of a concave lens determined? |
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Definition
| Since concave lenses diverge light it dioptic strength is determined by the relative rate at which it diverges light compared to the relative rate at which a convex lens converges light. |
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Term
| What is the result of combining a concave and convex lens with the same dioptic strength? |
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Definition
| The lenses will cancel each other out so that the total refractive strength will be 0 diopters |
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Term
| When calculating the strength of a cylindrical lens the axis of the lens must be given. If the focal line of a cylindrical lens if horizontal what is the degree of its axis? What if the focal line is vertical? |
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Definition
Horizontal is has an axis of 0 degrees
Vertical it has an axis of 90 degrees |
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Term
| What are the four refractive indices of the eye? |
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Definition
-the interface between air and anterior surface of the cornea
-the interface between the posterior surface of the cornea and aqueous humor
-interface between aqueous humor and anterior surface of the lens
-interface between posterior surface of the lens and the vitreous humor. |
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Term
| What is the total refractive power for the eye and how far in front of the retina does the central point lie? |
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Definition
Refractive power-59 diopters
Central point is 17 mm in front of the retina |
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Term
| Where does most of the refractive power of the eye come from? |
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Definition
| 2/3 of the refractive power of the eye comes from the anterior surface of the cornea. |
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Term
| What is the total refractive power of the lens and how does this compare to the total refractive power of the eye? |
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Definition
| The refractive power of the lens is about 20 diopters which is 1/3 of the total refractive power of the eye. The major importance of the lens in eye function therefore is not its refractive power its ability to change shape, increasing or decreasing in curvature, this allows for accommodation. |
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Term
| T/F The image that the eye forms on the retina is reversed and inverted compared to the image in the external visual world. |
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Definition
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Term
| How can the refractive power of the lens be increased from 20-34 diopter in young children? |
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Definition
| By changing the shape of the lens from moderately convex to very convex. |
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Term
| What forms the lens of the eye? |
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Definition
| A strong elastic capsule filled with viscous, proteinaceous, transparent fluid. |
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Term
| What holds the lens in place? |
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Definition
| Suspensory ligaments that attach radially around the eye, pulling the lens edge towards teh outer circle of the eyeball. |
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Term
| T/F. The suspensory ligaments are constantly tensed under resting conditions, pulling the lens into a relatively flat shape. |
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Definition
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Term
| What are the two sets of smooth muscle that make up the ciliary muscle? |
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Definition
| The meridional fibers and circular fibers. |
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Term
| How does the lens change shape when the meridional and circular fibers contract? |
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Definition
| When the meridional fibers contract the lens ligaments are are pulled forward and medially toward the cornea, releasing some of the tension on the lens. The circular fibers function like a sphincter and when they contract, they decrease the diameter of the circle to which the suspensory ligaments attach, thereby releasing tension on the lens. This allows the lens to take on a more spherical shape. |
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Term
| T/F. Under resting conditions, lens is pulled into a relatively flat shape. |
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Definition
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Term
| What portion of the nervous system controls the ciliary muscles? (parasympathetic or sympathetic; via which nerve) |
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Definition
| Parasympathetic via the III cranial nerve. |
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Term
| What effect do ciliary muscles have on the suspensory ligaments? |
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Definition
| Parasympathetic activity causes the ciliary muscles to contract, loosening the suspensory ligaments, allowing the lens to become thicker and increase in refractive power, therefore adapting the lens for focusing on nearby objects. |
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Term
| If an object is nearing the eye will parasympathetic firing increase or decrease? |
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Definition
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Term
| What cue might be used to correctly control accommodation? |
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Definition
| The degree of convergence of the eyes. When a nearby object must be focused on the eyes are strongly converged, when the object is further away the convergence of the eyes is reduced. |
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Term
| The lens of the eye loses the elasticity and therefore its ability to accommodate with ages. What is this known as and what are the approximate refractive strengths at 10, 45,and 70 years of age. |
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Definition
| Presbyopia is the decline in ability to accommodate. Refractive strength at 10 is 14 diopters, at 45 2 diopters, at 70 zero diopters. |
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Term
| What is the function of the iris? |
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Definition
| TO control the amount of light entering the eye. |
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Term
| What divisions of the autonomic nervous system control pupil dilation or constriction? |
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Definition
| Pupil dilation (mydriasis) is under the control of the sympathetic nervous system, and pupil constriction (miosis) is under control of the parasympathetic nervous system. |
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Term
| In regards to pupil size, when is depth of focus greatest? |
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Definition
| When the pupil diameter is smallest depth of focus is greatest. |
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Term
| Why does a small diameter pupil result in a larger depth of focus? |
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Definition
| When the pupil diameter is small, light rays allowed into the eye from a point source diverge very and light from objects far from the plane of focus are projected onto the retina with little scattering. |
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Term
| Why is the depth of focus smaller when the pupil diameter is large? |
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Definition
| The light rays which enter the eye from a point source diverge extensively. Consequently, light rays emitted from a point on an object behind (or in front of) the point of fixation are spread over a relatively large area of the retina, causing substantial blurring of the retinal image. |
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Term
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Definition
| Emmetropic eyes are normal. |
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Term
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Definition
| Hyperopia is farsightedness. |
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Term
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Definition
| Hyperopia is farsightedness and is caused by either an eyeball that is too short or occasionally by a lens system which is too weak. |
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Term
| Why can a person who is farsighted focus on distant objects, but not objects that are close by? |
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Definition
| Farsighted people focus on a distant object by using the accommodation mechanism. As they attempt to focus on closer objects through the accommodative power of the lens is used up as the ciliary muscle is contracted to its limit. |
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Term
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Definition
| Myopia is nearsightedness. |
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Term
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Definition
| Myopia (nearsightedness) is caused by either an eyeball that is too long, or (occasionally) by a lens system which is too strong. |
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Term
| What type of lenses are given to correct hyperopic eyes? |
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Definition
| Convex lenses because they add refractive power. |
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Term
| What type of lenses are prescribed to someone with myopic eyes? |
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Definition
| Convex lenses because they partially neutralize the power of the eyes |
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Term
| What is astigmatism and what causes it. |
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Definition
| Astigmatism is a refractive error which causes light from one plane to focus at a different distance than light from a plane at a right angle. Causes include uneven curvature of the cornea or an egg shaped lens. |
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Term
| T/F The accommodative power of the lens can compensate for astigmatism. |
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Definition
| False. Accommodative power of the lens cannot compensate b/c during accommodation the lens is changed equally in all planes whereas correction for astigmatism requires different degrees of accommodation in two planes. |
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Term
| How can astigmatism be corrected? What if the person also has hyperopia or myopia? |
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Definition
| With a cylindrical lens with an appropriate axis and strength. If the vision is further compromised by hyperopia or myopia then lenses with both spherical and cylindrical components are required. |
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Term
| What is an advantage to contact lenses or eye glasses? |
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Definition
| Contact lenses reduce the refraction which normally occurs at the anterior surface of the cornea. |
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Term
| Why are contact lenses particularly advantageous to a person with keratoconus or abnormally shaped cornea? |
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Definition
| In Keratoconus, a progressive thinning and bulging of the cornea, or an abnormally shaped cornea light refracts at an irregular pattern across the cornea. With a contact lens the tears fill the space between the contact and the cornea and replace the refractive index of the cornea. |
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Term
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Definition
| A cataract is a cloudy area of the lens. |
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Term
| How are cataracts corrected? |
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Definition
| If cataracts progress to the point that they severely inhibit vision then the lens can be removed and either an artificial lens replaces it or a convex lens is placed in front of the eye. |
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Term
| Where is visual acuity greatest? |
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Definition
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Term
| What are the two divisions of intraocular fluid? |
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Definition
-The aqueous humor-which lies in front of and to the sides of the lens
-The vitreous humor which lies between the lens and retina |
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Term
| Which section of eye fluid is free flowing? |
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Definition
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Term
| What is the vitreous humor mainly composed of? |
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Definition
| Proteoglycans giving it a gelatinous consistency. |
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Term
| How is the aqueous humor formed? |
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Definition
| Ciliary processes, folds the extend off of the ciliary body, are covered by secretory epithelial cells. The cells produce aqueous humor in a manner similar to the formation of CSF |
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Term
| Describe the path that aqueous humor flows through the eye. |
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Definition
| Aqueous humor is produced by the ciliary processes and flows between the suspensory ligaments, then through the pupil and into the anterior chamber of the eye. From here the aqueous humor flows into the angle between the cornea and iris, through the trabecular meshwork, into the canal of Schlemm and then into the venous circulation. |
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Term
| How is the normal intraocular pressure of 15 +/- 2 mm Hg maintained? |
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Definition
| Mainly through the amount of aqueous humor that is allowed to exit the canal of Schlemm. |
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Term
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Definition
| Eye diseases which result in vision loss due to an increase in intraocular pressure. |
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Term
| Why may increased intraocular pressure lead to blindness? |
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Definition
| Pressure on the optic nerve damages it. |
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Term
| What are ways to treat glaucoma? |
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Definition
| Surgical methods include increasing the rate at which the aqueous humor can leave the eye. Pharmacological treatments can decrease the rate of formation (beta-blockers, B-andrenergic receptor antagonists, carbonic anhydrase inhibitors) or increase the outflow from the eye (prostaglandin analogs and parsympathomimetics) |
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