INCIDENCE AND DISTRIBUTION OF REFRACTIVE ANOMOLIES

Question 1

What is the refractive error like at birth?

Answer 1

1. Normal distribution 
2. Skew towards hyperopia 
3. Myopia: 0-25% of newborns

Question 2

As an infant grows, refractive error shift towards 1. ______. However, by the time the child is about a year old, the refractive error skews towards 2. ____.

Answer 2

1. emmetropia due to eye growth

2. myopia

Question 3

What is emmetropization?

Answer 3

The process in which refractive error shifts towards emmetropia.

Question 4

When does ocular development slow down?

Answer 4

Ages 5-15

Question 5

Ages 5-15

Anterior chamber depth increases by only _____ mm

Answer 5

0.10 to 0.20 mm

Question 6

Ages 5-15

Vitreous chamber depth increases by

Answer 6

~1 mm

Question 7

Ages 5-15

Axial length increases by

Answer 7

~1 mm

Question 8

Ages 5-15

Cornea is stable or unstable?

Answer 8

STABLE

Question 9

Ages 5-15

Lens power decreases by ____ (lens thins, but still grows new fibers) 

Answer 9

2 D

Question 10

Ages 5-15

Hyperopia decreases by

Answer 10

~1 D

Question 11

Emmetropization: Age 5-15 

Prevalence of myopia increases by over___times to __%

Answer 11

7 times to 15%

Question 12

Juvenile-onset myopia: increase _____/ year during early teens

Answer 12

~ -0.50 D

Question 13

Adult-onset myopia: ___% of population is myopic after teen years

Answer 13

10%

Question 14

Total myopic prevalence in adult population is ~__%

Answer 14

~25%

Question 15

9 possible factors that affect refractive error distributions:

Answer 15

1. Age 
2. Gender 
3. Ethnicity 
4. Geography 
5. Diet 
6. Time 
7. Personality 
8. Systemic Conditions 
9. Ocular Diseases

Question 16

What is the single most important determinant of distribution of refractive error in a given group?

Answer 16

Age

Question 17

What do studies show about how gender effects refractive error distribution?

Answer 17

Gender 
Trends in refractive error distribution are inconclusive  Studies have shown: no significant differences, shift towards males, shift towards females

Question 18

What do studies show about how ethnicity effects refractive error distribution?

Answer 18

Not enough data

Prevalence of Myopia: Asians > Caucasians > African-Americans

Question 19

What do studies show about how geography effects refractive error distribution?

Answer 19

Study results are confounded by other factors (ex. diet, education) 

Similar to trends found in US ethnicity studies
Alaska/Eskimo has most myopia at 44.7%

Question 20

What do studies show about how diet effects refractive error distribution?

Answer 20

Diet 
Effects on refractive error is unclear, due to confounding factors (ethical dilemma to alter nutritional needs of children)

Question 21

What do studies show about how time effects refractive error distribution? What is it’s overall trend?

Answer 21

Inconclusive, as studies are done in different decades with different research methods and different refractive error criteria 

Overall trend: decrease in prevalence of myopia with increasing age in elderly range

Question 22

What do studies show about how personality effects refractive error distribution?

Answer 22

No strong data!
Myopia is associated with:  
Introversion  
Inhibited disposition  
Disinclination for motor activity and social leadership  

Hyperopia is associated with:  
Carefree  
Impulsive  
Hyperactive  
Socially passive

Question 23

What do studies show about how systemic conditions effects refractive error distribution?

Answer 23

Effect the development of the eye  affects its refractive state

Examples: Albinism, Down Syndrome, Connective Tissue Disorders, Diabetes, Homocystinuria (metabolism issue with excretion of homocystine in the urine and excesses of homocystine and methionine in the blood)

Question 24

What do studies show about how ocular disease effects refractive error distribution?

Answer 24

Clear visual input needed for normal emmetropization to occur 

Majority of conditions are associated with myopia

Conditions associated with hyperopia; involves foveal development: Albinism, Maculopathies, and Rod monochromacy

Question 25

What are the factors have a known affect on refractive error distributions?

Answer 25

Age
Systemic Conditions
Ocular Diseases

Question 26

Studies of Parents & Children show higher heritabilities in:

Answer 26

Axial Length 

Corneal Power

Question 27

Studies of twins show higher heritabilities in:

Answer 27

Axial Length 
Corneal Power 
Refractive Error

Differences between twins is smaller for Monozygotic (identical) than Dizygotic twins

Question 28

Near Work Theory 

Excessive reading during childhood causes abnormal eye growth leading to myopia. What are studies that support this?

Answer 28

Studies supporting this: 

1. Increase in myopia prevalence in first school-educated Eskimos 
2. Decrease in myopia prevalence during WWII in Japan 
3. Adult-onset myopia in college populations

Question 29

Excessive Axial Elongation and Myopia is linked to:

Answer 29

schooling, studying, reading, and other near work

Question 30

How does intelligence seem to trend with myopia?

Answer 30

Myopes tend to have higher scores on tests of intelligence & cognitive ability and get better grades than other refractive error groups.

Question 31

How might socioeconomic status effect myopia?

Answer 31

Myopes tend to be overrepresented among the higher socioeconomic strata and underrepresented among the lower income levels 

Possibly due to connection between Myopia, Intelligence, and Educatio