REFRACTIVE ERROR  (images are not focused clearly)
Hyperopia (far-sightedness), myopia (near-sightedness),  astigmatism (distorted vision) and combinations of the aforementioned are known as refractive errors.  For proper eyesight, the cornea (the clear window in front of the eye) and the lens (behind the pupil) must properly focus or "refract" light onto the retina (at the back of     the eye).  If the length or shape of  the eye is not ideal, the light may get focused too far forwards, or too     far back leaving a blurred image on the retina.  In an eye without refractive error that is looking in the distance, the focusing muscle does not have to work.
HYPEROPIA (far-sightedness)  Short eyeball.  Light  focussed too far back
Hyperopia is the inability to see clearly in the     distance or up close without having to strain the focusing muscle of the     eye.  It requires less strain to focus distance objects than near ones, so older adults with hyperopia see more easily far away than up close.  Children  with hyperopia have less trouble focusing up close than adults because the youthful strength of their lenses can overcome the shortness of the     eye.  However children with high hyperopia may have inturned eyes unless given glasses.   Adults with hyperopia may also get     crossed eyes if they do not use their proper contacts or glasses.  Non-visual signs of hyperopia include     headaches, and eye strain.         
     Treatment for hyperopia is not  necessary unless the patient is having discomfort, vision difficulty, or  crossed eyes.  Patients with high hyperopia,  eye strain, headaches or crossed eyes should wear glasses or contact lenses     as the usual treatment for hyperopia.
     Adults with hyperopia find it  especially difficult to accept glasses or contacts because they used to enjoy     good spectacle-free vision in their youth      Because adults are so used to straining their eyes, they may find it     difficult to adjust to glasses.  It  is not uncommon that older adults with hyperopia, who never had to wear     glasses/contacts in youth, travel from doctor to doctor seeking a solution  to their problem.  Unfortunately  there is no "Fountain of Youth".      (Laser treatment exists, but is not yet a perfect technology)
MYOPIA (near-sightedness)        Long eyeball.        Light focused too far forward.
Myopia is the inability to see objects in the distance clearly.  Objects at near are seen more clearly than ones in the distance.
     Myopia is a partly inherited condition which often begins in childhood.  Few factors outside of heredity affect       this condition. Using dim light, reading too much and nutritional deficiencies do NOT seem to cause myopia. 
    Myopia is best treated with eyeglasses and contact lenses which compensate for the elongated shape of the eye allowing the light to focus properly on the retina.   As children (and their eyes) grow especially as teenagers, the condition typically worsens and then levels off in adulthood.  Children who are growing quickly may need prescription changes as often as every 6 months to correct the problem.   Parents who are often proud of their children growing tall, regard with dismay the growth of the eye, and worsening of myopia.  However the eyes will grow just like the other body parts of children.   As little as 1 mm of growth in the length of the eye will change       the prescription by 3 units!   
     There is no scientific evidence that contact lenses or eye exercises stop the progression of myopia. Laser refractive surgery is available as a treatment for myopia but is not recommended for growing children.  Furthermore patients must understand the risks involved in these procedures, and that the long term effects of       this relatively new technology over the lifespan of a patient are unknown.
PRESBYOPIA (aging eyes)
     As patients age, they will have difficulty focusing their eyes for reading or close work, whether or not       they are far-sighted. This is called presbyopia and is part of the normal aging process. Presbyopia usually affects people over the age of forty as  the lens of the eye starts to lose some of its flexibility.  Patients that are far-sighted       (hyperopia) notice reading difficulties sooner than other people.       
     Presbyopia is easily corrected with eye glasses of increasing strength as a person ages. Reading       glasses, bifocals, trifocals or progressive lenses (invisible bifocals)  may be prescribed to patients with presbyopia.
     Bifocal contact lenses are  available, but may not offer the crispest vision.  In lieu of bifocal contacts some       patients may choose monovision contact lens.  With monovision one eye is adjusted for distance, and the       other for near.  Near sighted  patients may get away with using a contact in only one eye for distance  vision, with the non-corrected eye being used for reading.  Alternatively patients who love their  contacts, can continue using the contact lens prescription of their  younger years and put reading glasses on top as needed.
     Surgery for presbyopia correction  is not conventional, and if patients choose this method of treatment,       they should fully realize the risks involved. 
ASTIGMATISM (warped  cornea/lens)
     An  optically perfect cornea (the clear window in front of the eye) is smooth and equally curved in all directions.      With astigmatism, the cornea is "warped" that is,  it curves more in one direction than the     other.  This warpage distorts the focus of objects causing blurry vision at all distances.  Large amounts of astigmatism are usually inherited,  present at birth and frequently remain unchanged throughout life. Small  amounts of astigmatism can be acquired any time in life and are, in fact,     very common. It often does not require correction.  Progressive increasing astigmatism can     be seen with keratoconus.        
     Correction of astigmatism is   less difficult if the distortion proceeds across the cornea in a regular     direction. Prescription glasses can often be ordered that neutralize or off  set the distortion to the cornea.    It may require patients a while to get used to their astigmatism  correction, and complaints of eye strain, or bending of straight line     objects are common.
     If the distortion is irregular, only   reshaping the cornea will correct the problem. This is usually done through     the use of hard contact lenses or by replacing the cornea with donated  human corneal tissue. While hard contacts lenses are usually better than     soft lenses for this correction, some special soft lenses may be helpful to     correct mild astigmatism. Large amounts of astigmatism are not easily  corrected with contacts since contacts may wobble on the uneven surface of   the cornea. In such instances, a special contact called a toric lens may be     ground with a curve on the back surface which stabilizes the lens on the  cornea.