Myopia and Hyperopia, are eye problems caused
by a failure of the eyes to correctly focus.
Myopia is nearsightedness while hyperopia is better
known as farsightedness.
They are refractive error conditions of the eye.
Refractive disorders of the eye
Refractive disorders occur when the eye fails to
refract properly for focusing on the fovea of the
retina. Theoretically, refraction means the bending
of light but in medical terms, it refers to the method
of measuring the strength of the lens needed.
Refraction occurs when light slows down when it
travels from one medium to another of greater density.
All the light particles slow down concurrently when
light hits a flat surface at right angles. Hence,
it continues to travel in a straight line.
However, if light hits a surface at an angle, the
particles that first enter the new medium slow down
first and the rest follow. This causes light to bend.
So, when light passes from the air into the cornea
(the two mediums have a huge difference in density)
it refracts and then focuses onto the retina with
the help of the lens of the eye. The eye needs to
accommodate in order to refract light from various
objects, angles and distances. Hence, the lens of
the eye accordingly adjusts its power for focusing
also known as hypermetropia or farsightedness,
occurs when the power of the eye is weaker and
is too small. Hence, the eye cannot focus properly
on near objects, and in extreme cases, it cannot
focus on objects at any distance. The eye needs
to increase its power in order to focus the image
(on the retina) of an object that moves towards
it. In hyperopia since the eye power is less, the
image is blur.
Clinical characteristics of hyperopia
Hyperopia is marked by blurring, asthenopia,
adjusting problems, binocular errors, amblyopia
Correction of hyperopia
For adults with hyperopia the standard treatment
is with ‘plus’ lenses, but surgery
is also an option. LASIK is the most popular
procedure for the correction of mild and moderate
hyperopia. For severe cases, clear lens exchange
in addition with intraocular lens implantation,
remains the commonest line of treatment.
However, there are no established guidelines
for the degree of hyperopic refractive error
that requires prescriptions. Mild hyperopia is
often not given a prescription, especially in
children. This is because various researches
have shown that the eyes is elastic and will
adjust in order to offset for the existence of
anisometropic refractive corrections. However,
too much strain to adjust may result in the risk
of cross-eyes or convergent squint in children.
Hyperopia when left untreated also carries a
high risk of also developing glaucoma.