One of the things that ECPs can count on
is the fact that the human visual system will change as one
ages. Myopic, hyperopic, presbyopic and astigmatic changes
allow us to regularly provide the needed eye care to
facilitate those changes. We are also fortunate to have
products such as clear and colored plastic lenses,
polycarbonate, Trivex, Transitions lenses, soft contact
lenses, and gas permeable contact lenses to help those
people in need. Lens treatments with ultraviolet protection
or anti-reflective coating can also add a comfort level to a
minus or plus prescription.
Besides refraction changes that occur
throughout our lifetime, vision problems can occur due to
the aging of the different anatomical structures of the
human eye. There are functional developmental changes that
occur as a newborn ages including the ability to determine
sizes, shapes, orientation, and distances of objects. Some
visual abilities are inherited, some are learned, and some
are affected by one’s environment. Within hours after
birth, a child can move their eyes together and make
compensatory eye movements in response to head movements.
By 2 months of age accommodation and
convergence can be demonstrated. There is rod and cone
function in infants, although the time when color vision is
actually achieved is debatable. Some experts state that
color vision does not develop before the age of 4-6 months.
Experts have some disagreement as to whether color vision is
actually present or if this is a learned cortical/brain
function which has not developed fully at this very young
age.
Other researchers have stated that red,
blue, and green cone functioning may be present from 7-11
weeks of age. Other changes that will occur through the
growth and early maturation process include acuity and
pattern vision, spatial vision, perceptual-motor skills,
cognition and learning, the ability to understand language,
and to read.
According to Dr. Jack Richman, “The
earlier in life that deficits in visual acuity can be
determined, the better are the chances in finding visual
disorders that may have a harmful effect on the child’s
learning and developmental process.” The National Society
for the Prevention of Blindness estimates that 5% of the 3-5
year age group has vision problems, even though the eye is
at an adult stage by age 3. Growth can still occur to a
lesser degree after this age. The length of the eye
increases from its size at birth to approximately 28
millimeters by the ages of 8 to age 13, with most of the
growth reached by age 8-9. The prevalent vision disorders in
the preschool population are myopia-1%, hyperopia-7%,
astigmatism-2%, anisometropia-2%, and amblyopia-1.5-2%. 67%
of infants show 2-3 diopters of against-the-rule astigmatism
with retinoscopy but by age 1-2, the astigmatism flips to a
small amount of with-the-rule astigmatism.
Perhaps the most active period for
changes in the magnitude of refractive errors is during the
first years of life. Large fluctuations can be seen
especially in children with anisometropia or astigmatism.
Studies done by Dr. Hirsch and Dr. Baldwin found that
females exhibit myopia at an earlier age than males. From
ages 6-11, girls have a higher mean refraction, but at age
11 the trend reverses. A higher percentage of females show
refractive changes from age 6-13. At age 13-17, females were
found to show less of a change towards myopia than males. At
age 5-6, hyperopia increases for both females and males, but
after this age hyperopia decreases more for males than for
females. More females reveal myopia by ages 10-13 than
males, but this number increases in males after age 13.
The presence of high myopia in premature
infants was first identified with a condition called
retrolental fibroplasia (retinopathy of prematurity-ROP) due
to the use of high amounts of oxygen used in incubators. A
study that was published in the American Journal of
Ophthalmology by Dr. M.C. Fletcher and Dr. S. Brandon found
that all premature infants had myopia whether they were
affected by retrolental fibroplasia or not. Premature
infants weighing more than 3.74 pounds had myopia ranging
from 0.25 to 6 diopters. Those premature infants weighing
less than 2.75 pounds had myopia ranging from 10 to 20
diopters. One of the first large-scale studies of the
refraction of 370 newborn infants was done by Dr. R.C. Cook
and Dr. R.E. Glassock and was also published in the American
Journal of Ophthalmology. The refractive error findings were
diverse, ranging from 11-12 diopters of myopia to 11-12
diopters of hyperopia.
Eye care professionals have always known
that myopia was determined by the axial length of the eye
combined with a possibly steep cornea or crystalline lens.
But new research at the Ohio State University College of
Optometry is finding that myopia develops in children when
the crystalline lens stops adapting to the eye’s continued
growth. According to Dr. Donald Mutti, “this work is
trying to show that it is not just about the length of the
eye, it is how the length of the eye relates to the rest of
the eye. The onset of myopia is really a sudden occurrence
of an imbalance between the growth of the eye and the
development of the crystalline lens.”
This research was published in the March
issue of Optometry and Vision Science. Dr. A. Sorsby, Dr. B.
Benjamin, and Dr. M. Sheridan concluded that the growth of
the eye during infancy is extremely rapid. The length of the
globe increases 5 mm from 18-23 mm between birth and age 3.
Between the ages of 3 and 13, the increase in axial length
averages about 0.1 mm per year. In studies done of 333
school children age 6-8, Dr. G. Kemph, Dr. S. Collins, and
Dr. B. Jarman found that the great majority of children are
emmetropic. The refractive error distribution of this age
group was 2 diopters of myopia to 3.75 diopters of hyperopia
with a peak incidence of 1 diopter of hyperopia.
In a study published in the American
Journal of Optometry, Dr. M.J. Hirsch concluded that “if a
child has any myopia at all at ages 5-6, the myopia will be
sure to remain and will probably increase. If a child has
hyperopia in excess of +1.50 diopters at age 5-6, that child
will very likely remain hyperopic by ages 13-14. If a child
has a spherical refraction between +0.50 and +1.25 diopters,
there is a great chance of being emmetropic by age 13-14. If
a child has a spherical refraction between 0 and +0.50
diopters at age 5-6, then there is a high probability of
becoming myopic by age 13-14. This probability becomes even
greater if against-the-rule astigmatism is present.”
In another study, Dr. Hirsch found that
the percentage of children having with-the-rule astigmatism
was 16-20% for all age groups. The percentage of those
children having against-the-rule astigmatism increased from
3-11% during their school years. In a study done by Dr.
Matsumura and Dr. Hirai of Japanese students age 3-17, the
prevalence of myopia increased from 43.5% at age 12 to 66.0%
by age 17.
Their results showed a considerable
increase in the incidence of myopia among those 7 years of
age or older and there was a greater shift towards myopia
especially in students older than 10 years of age. Other
studies done showed a considerable increase in the incidence
of myopia among those 7 years of age or older, and changes
in mean refractive errors also demonstrated a greater shift
toward myopia, especially in students older than 10 years.
Also, the prevalence of myopia increased from 49.3% to 65.6%
in 17-year-old students.
The National Center for Health Care
Statistics states that other eye problems in this age group
include inflammation, eye injuries, allergy problems,
strabismus, congenital disorders, convergence and divergence
problems, tropias, and amblyopia. Medical eye problems that
may require special attention and higher levels of primary,
secondary, and tertiary eye care include blocked tear ducts,
Sturge-Weber’s syndrome, ptosis, congenital cataracts, and
congenital glaucoma. Red eyes, conjunctivitis, projectile
eye injuries, sports injuries, and blepharitis are commonly
seen by eye care professionals.
Serious problems include children
affected by HIV, juvenile rheumatoid arthritis, juvenile
diabetes, juvenile hypertension, retinoblastoma,
toxocariasis, crack/cocaine affected children born to
addicted parents, fetal alcohol children born to alcoholic
parents, learning disabled children including autistic and
Down’s Syndrome children, children born with birth defects
or other chromosomal anomalies, hyperactive or emotionally
challenged children, hearing impaired children, dyslexic
children, and children with seizure disorders, Lupus
erythematous, multiple sclerosis, Guillan-Barre syndrome,
Stevens-Johnson syndrome, malnutrition problems and color
vision problems.
As ECPs we should remember that this
population group may need special attention in order to
prevent a lifetime visual disability. Statistics and data
are important in allowing us to have a guide as to what to
expect in a certain population group. No matter what the age
of any patient, each patient has their own unique needs,
identities, personalities, and characteristics. This is why
our jobs are rewarding and challenging. And we are fortunate
to have the opportunity to meet those challenges as well as
to reap the rewards professionally.
