Before we can describe hypermetropia let’s compare the eye ball to a camera for better
understanding. When we take a picture, light after reflecting
from an object enters the camera and passes through;
First, a transparent glass in front of the aperture of the camera then secondly, a lens
that helps us in focusing light rays and lastly,
a film on which light is focused for a clear picture.
Eye is somewhat similar, as when we see an object, light after reflection from that object
enters our eye through;
Firstly, cornea (the transparent curved front part of eye) then secondly, through the crystalline
lens that helps us in focusing light rays and lastly, the retina (light sensitive receptor
cells in the posterior part of eye ball) on which light
is focused for a clear image. Definition
It is a form of refractive error (inability to refract/ bend/focus the light rays properly)
in which parallel rays of light (i.e. Coming from a
distinct object) after entering the eye are focused
behind the retina with accommodation (eye muscles) at rest.
Key features This refractive error has three key features
1. image is formed behind the retina, as in normal people image has to be focused on the
retina for it to be clear. 2. Parallel light rays (the rays that only
come from objects at 6 meters or beyond) must be used for assessment. As when objects come
closer than 6 meters, light rays start to diverge, changing their focus. That is
why we place Snellen’s chart at 6 meters. 3. Eye is must be at rest.
Just like a DSLR camera’s focusing power can be change by rotating its zoom lens, eye
changes its focusing power by changing the shape of its lens with the help of contraction
and relaxation of certain muscles located inside the eye ball. These muscles must be
at rest to correctly access the eye’s focusing
Both hypermetropia and myopia have abnormal distant vision i.e. they cannot focus distant
objects clearly. But a unique thing about hypermetropia is
that if these patients increase the power of their lens
(by contraction of certain intraocular muscles) they can focus the image accurately on their
retina. This will result in excessive and continuous
use of intraocular (ciliary) muscles in order to keep
the image focused on retina resulting in pain. Also, when they try to see a near objects
their eyes will require even more focusing power
which these muscles can no longer provide hence
causing near objects to become blurry. (This is also the reason why we use cycloplegic
(or muscle paralyzing) drops before estimating the amount of refractive error)
So, a lot of hypermetropic patients (not all) (with less degree of hypermetropia) will say
that they see distant objects clearly but they have
pain/discomfort in their eyes or their eyes get tired and
also near vision is mostly not that good. Hence these patients are mistakenly called
far sighted. CAUSE
1. Curvature: curvature of cornea or lens is flatter than normal.
2. Axial: short axial length of eye 3. Index: decrease in refractive index (i.e.
light bending/focusing power) of the lens (e.g. in cortical cataract)
4. Positional: posterior displacement of lens e.g. after trauma.
5. Aphakia : absence of lens in eye….therefore eye cannot focus light rays on retina. TYPES
Total hypermetropia is the total refractive error calculated after complete cycloplegia
(intraocular muscle paralysis) induced by certain drops.
1. Latent hypermetropia. amount of hypermetropia corrected by (the focusing
power produced due to) normal tone of intraocular (ciliary) muscles (It is
usually 1 diopter) 2. Manifest hypermetropia it is the remaining
portion of hypermetropia. Divided in to Facultative amount of hypermetropia corrected
by (the focusing power produced due to) active contraction of intraocular
(ciliary) muscles. Absolute amount of hypermetropia that cannot
be corrected even by contraction of intraocular (ciliary) muscles. CLINICAL FEATURES
SYMPTOMS Eye straining or discomfort (asthenopia) including
: eye tiredness, pain, headache or mild photophobia.
Blurred vision with eye straining: when muscle contraction attempts but fails to
correct hypermetropia. Blurred vision only: when refractive error
is high and cannot be corrected at all by muscle contraction efforts.
inward deviation of eye (convergent squint) (normal pts require to move their eyes
inward while focusing near objects….. this is enhanced in hypermetropic pts
causing their eye to move inwards intermittently or constantly) SIGNS
small eye ball corneal diameter may be small
Retinal exam might show false changes due to distortion of image when hypermetropia
exceeds 5 diopters DIAGNOSIS
Retinoscopy (a hand-held device that throws light in the eye and allowing us to observe
its movements and reflection, hence helping to confirm the refractive error)
A-scan (a small ultrasound probe that throws US waves in the eye ball and then detects
their reflections or echo timings, calculating the eye ball length) short length
NOTE: At birth all eyes are hypermetropic (+2.5
to +3) i.e. light is focused behind the retina. As the
eye ball grows and at about 6-7 yrs age eye ball is of normal size and emmetropic i.e.
light is focused on the retina. Some people it continues
to grow causing myopia i.e. light is focused in front of retina.
TREATMENT Unlike the camera, maximum (2/3rd ) focusing in an eye is done by the transparent
front part (cornea) while the rest (1/3rd ) is done by the lens. So, while treating these patients we have
to increase the focusing power of the eye so that
image is formed on the retina instead of in behind it. This can be done by using either
a converging lens e.g.
NON-SURGICAL treatment Glasses
Contact lenses Or some surgical procedure can be done to
increase the focusing power of either the cornea or
the lens. SURGICAL TREATMENT
1. making the central part of cornea more curved. This include different methods that
were changed and advanced depending upon reduction of side effects and recovery time
and improvement of degree of vision. PRK (Photorefractive keratectomy)
Remove corneal epithelial cells by a solution then use laser to reshape cornea (i.e.
making it steeper) and then apply a bandage contact lens. Side effects include
pain and recovery is in 1 week at least. It corrects 2D hypermetropia LAS I K (Laser In-situ Keratomileusis): corrects
up to 4D A famous and frequently performed surgery
nowadays. In this procedure a bigger flap of cornea 160 micrometer is taken by
a device (keratome), laser is applied to change the corneal shape and then the flap
is repositioned. Advantages over other procedures
-Absence of post-operative pain -More rapid visual rehabilitation
Conductive keratoplasty: it involves giving radiofrequency energy to corneal
stroma causing change in its shape. Can correct low to moderate hypermetropia.