PEAVC 3

• Refractive status

  Signifies either the relationship of the refracting system of the eye to its axial length by indicating the focal length of the eye, or the position of its principal focus as compared to the position of the retina, with the positive accommodation inactive

  
• Static refraction

  Measurement of the relationship of the posterior principal focus of the eye's refractive mechanism and the retina of the same eye with accommodation relaxed or at rest

  
• Dynamic refraction

  Accommodation is not at rest. Refractive power of the eye is determined
• Refractive anomalies, errors of refraction


  Variations from perfect coincidence of the principal focus of the eye with the retina

  
• Emmetropia

  • Refractive status with accommodation at rest, wherein incident parallel rays of light converge to form the circle of least confusion upon the retina
• Ametropia

  • Refractive status with accommodation at rest, wherein incident parallel rays of light converge to form the circle of least confusion is formed in front of the retina (Myopia) or behind the retina (Hyperopia)
• Premature infants over 1,700 gms at birth exhibited myopia of 0 to 6.00 Diopters which stabilized at 4 to 6 weeks of life and then altered towards Emmetropia
• Premature infants under 1,250 gms at birth showed higher myopia of -10.00 to -12.00 Diopters which reduces in a few months and neared myopia in a year
• Newborn infants have a high incidence of hyperopia and myopia is rare at birth
• Newborn infants have a high incidence of myopia which reduces to hyperopia by the end of the first year
• Newborn infants with myopia present at birth usually disappears within the first year
• 98% of 4 year old children are hyperopic
• There is a decrease in hyperopia in school children
• The trend is toward hyperopia than toward myopia in adults. Hyperopia increases from age 45 to 70. Over the age of 65 to 70, the trend is toward myopia, probably because of changes in the crystalline lens index and substance
• Nearsightedness (Myopia)

  Occurs when light entering the eye focuses in front of the retina instead of directly on it. Caused by a cornea that is steeper, or an eye that is longer, than a normal eye. Nearsighted people typically see well up close, but have difficulty seeing far away.

  
• Nearsightedness

  • Often discovered in school-age children who report having trouble seeing the chalkboard
  • Usually becomes progressively worse through adolescence and stabilizes in early adulthood
  • An inherited problem
• Farsightedness (Hyperopia)


  Occurs when light entering the eye focuses behind the retina, instead of directly on it. Caused by a cornea that is flatter, or an eye that is shorter, than a normal eye. Farsighted people usually have trouble seeing up close, but may also have difficulty seeing far away as well.

  
• Farsightedness

  • Young people with mild to moderate hyperopia are often able to see clearly because their natural lens can adjust, or accommodate to increase the eye's focusing ability
  • As the eye gradually loses the ability to accommodate (beginning at about 40 years of age), blurred vision from hyperopia often becomes more apparent

  
• Astigmatism

  Means that the cornea is oval like a football instead of spherical like a basketball. Most astigmatic corneas have two curves – a steeper curve and a flatter curve. This causes light to focus on more than one point in the eye, resulting in blurred vision at distance or near.
• Astigmatism

  • Often occurs along with nearsightedness or farsightedness
• Presbyopia

  Also known as the "short arm syndrome", is a term used to describe an eye in which the natural lens can no longer accommodate. Accommodation is the eye's way of changing its focusing distance: the lens thickens, increasing its ability to focus close-up. At about the age of 40, the lens becomes less flexible and accommodation is gradually lost.

  
• Presbyopia

  • Most people first notice difficulty reading very fine print such as the phone book, a medicine bottle, or the stock market page
  • Print seems to have less contrast and the eyes become easily fatigued when reading a book or computer screen
  • Early on, holding reading material further away helps for many patients
  • Eventually, reading correction in the form of reading glasses, bifocals, or contact lenses is needed for close work
• 20/20 vision

  The numerator is the distance in feet the patient is from the eye chart. The denominator represents the distance an eye with "normal" vision can read the same line. If you can read the 20/40 line, you're able to see at 20 feet what a normal eye could see at 40. And if your vision is 20/16, you're above average because you can see an object from 20 feet that a normal eye sees at 16.

  
• Refraction

  A vision test that determines your best visual acuity with corrective lenses. It is typically done using an instrument called a phoropter which holds corrective lenses that are positioned in front of your eye.

  
• Astigmatism is a term that relates to the cornea
• Astigmatism causes blurred vision

  
• An astigmatic cornea is shaped most like a football
• Astigmatism can occur along with both nearsightedness and farsightedness
• Astigmatism can be corrected with both surgery and glasses
• Hypermetropia


  Refractive state of eye where parallel rays of light coming from infinity are focused behind the sentient layer of retina with accommodation being at rest

  
• Hyperopia


  Also called longsightedness
• Hypermetropia first suggested by KASTNER

  1755
• Hypermetropia


  • Posterior focal point is behind the retina which receives a blurred image

  
• Causes of hypermetropia

  • Axial
  • Curvature
  • Index
  • Positional
  • Absence of lens
• Axial hypermetropia


  Most common, total refractive power of eye is normal but axial shortening of eyeball

  
• Curvature hypermetropia

  Flattening of cornea, lens or both
• Index hypermetropia


  Change in refractive index with age, physiologically in old age or pathologically in diabetics under treatment
• Positional hypermetropia


  Posteriorly placed crystalline lens, occurs as congenital anomaly or result of trauma/disease

  
• Absence of lens


  Causes hypermetropia
• Clinical types of hypermetropia

  • Simple hyperopia
  • Pathological
  • Functional