Eye Conditions

Refractive Errors
What are refractive errors?

the_eye copyFor our eyes to be able to see, light rays must be bent or “refracted” so they can focus on the retina, the nerve layer that lines the back of the eye. The cornea and the lens refract light rays. The retina receives the picture formed by these light rays and sends the image to the brain through the optic nerve. A refractive error means that the shape of your eye doesn’t refract the light properly, so that the image you see is blurred. While refractive errors are called eye disorders, they are not diseases. In a normal eye, the cornea and lens focus light rays precisely on the retina.

What are the different types of refractive errors?

 myopia1 copyMYOPIA(nearsightedness): A myopic eye is longer than normal or the cornea has too much focusing power, so that the light rays are focused in front of the retina. Close objects look clear but distant objects appear blurred. This condition affects over 25% of all people in the United States.


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HYPEROPIA(farsightedness): The opposite of myopia. The eye is shorter than normal or the cornea lacks refractive power. Light rays are focused behind the retina and close objects are blurry.



ASTIGMATISM: This condition blurs and distorts both distance and near objects. A normal cornea is round and smooth (like a basketball). With astigmatism, your cornea is curved more in one direction than in the other (like an egg or football). You can have astigmatism in combination with myopia or hyperopia.

PRESBYOPIA(aging eyes): When you are young, the lens in your eye is soft and flexible. The lens of the eye changes its shape easily, allowing you to focus on objects both close and far away. After the age of 40, the lens becomes more rigid. Because the lens can’t change shape as easily as it once did, it is more difficult to read at close range. This normal condition is called presbyopia. You can also have presbyopia in combination with myopia, hyperopia, or astigmatism. No exercise or medication can reverse presbyopia.

How are refractive errors corrected?

Eyeglasses: phoropterGlasses are an easy method to correct refractive errors. They can also help protect your eyes from harmful light rays, such as ultraviolet (UV) light rays. A special coating that screens out UV light is available when you order your glasses. Bifocals are glasses that are used to correct presbyopia. They have correction for reading on the bottom half of the lens and another for seeing distance on the top. Trifocals are lenses with three different lens corrections in one set of eyeglassses. If you don’t need correction for seeing distance, you can buy over-the-counter reading glasses to correct presbyopia.



A cataract is a clouding of the normally clear lens in the eye.  This is a normal aging process which blocks light from entering the eye, and causes vision problems such as glare, halos, and difficulty reading.  Read more about cataracts.

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This is a ‘mature’ cataract.  Note the opacities in the the normally black pupil.




gl_eye copyWhen pressure within the eye increases and damage to the optic nerve (in the back of the eye) results, this is called Glaucoma. There are several types of glaucoma and several ways to treat it.  If discovered in time, vision loss usually can be prevented.  Sierra Eye Associates is proud to have the only Glaucoma Subspecialist in all of Northern Nevada, in Dr. Michael Stanko.  Please visit our Glaucoma Page to learn more.


Pediatric ophthalmology is a subspecialty area of ophthalmology which concentrates on the diagnosis, management, and treatment of ocular disorders frequently encountered in childhood.  Some of these conditions include Amblyopia (lazy eye), Strabismus (eye misalignment)), prematurity, and genetic/inherited disorders (such as retinitis pigmentosa).  Sierra Eye Associates is the only practice to have two Pediatric Ophthalmologists on staff to serve the Northern Nevada community with Dr. L. Alan Johnson, and Dr. Pauline Hong.  Please visit our Pediatric section for more information.


Diabetes mellitus is a condition which interferes with the body’s ability to regulate sugar metabolism.  As a result, medium to small blood vessels throughout the body become damaged.  One common area of blood vessel damage is in the retina of the eye.  Diabetic retinopathy, as it is called, can lead to severe vision loss and even blindness if not diagnosed and treated correctly.  Please visit our web page on diabetic retinopathyfor more information. 

Macular Degeneration

Age Related Macular Degeneration (ARMD) is a disease that affects the retina of the eye.  This condition is probably hereditary in nature, but the only known association is advancing age.  The retina is the inner lining of the back of the eye, like the inside of the wall of a basketball.  The retina works like film in a camera.  The central part of the vision, that part used for reading, is served by a portion of the retina called the macula.  This is the area involved in ARMD.

Floaters and Flashes of Light

This is a common condition frequently seen after the age of 50, although it can occur earlier in life.  It results from a change in the jelly (vitreous) in the back of your eye.  The jelly liquefies and can pull on the retina as it does so. This ‘vitreous detachment’ from the retina can cause flashes of light and subsequent floaters.

Sometimes, however, this normal occurrence can cause a tear in the retina or even a detachment of the retina. It is therefore recommended that a complete ophthalmic examination with pupil dilation be performed if flashes and floaters are noted, to rule out retinal problems.

Please call (775) 329-0286 if you would like to schedule an appointment.