Prof. Dr Zeinab El Sanabary
Conjugate foci Automated Refractors
Near-sightness means that either the eye is too long or
the optics are too strong.
In either case the light from a distance object focuses in
front of the retina.
Minus or concave lenses are used to move the image
back on the retina when viewing distance objects.
The vision may be corrected with glasses, contact
lenses or refractive surgery.
Clearly if your parents are nearsighted you have a better
chance of becoming nearsighted.
Identical twins have similar refractive errors.
Anterior displacement of the lens
Simple : no progress
Hereditary, F, Racial
Retinal breaks & RD
Much more common in people with a higher
Most myopia develops during periods of
accelerated growth (8-19).
Previously myopia stopped by the early
twenties. Today, we see more myopia
progressing in the late twenties or thirties in
those patients who spend a long time reading or
Correction of Myopia
Glasses with minus concave lenses (the
Clear lens extraction
Posterior lens displacement
Components of Hypermetropia
Total: with total cycloplegia
Latent: corrected by the tone of the
Manifest: highest + lens with max VA
Facultative: overcome by accommodation
Absolute: lowest + lens with best VA
Fundus: water silk reflex, Pseudoneuritis
Astigmatism is very common. Some
experts believe that almost everyone has
a degree of astigmatism, often from
birth, which may remain the same
The exact reason for differences in
corneal shape remains unknown, but the
tendency to develop astigmatism is
inherited. For that reason, some people
are more prone to develop astigmatism
With the rule
Against the rule
What causes astigmatism?
Astigmatism usually occurs when the cornea, has an
Normally the cornea is smooth and equally curved in all
directions and light entering the cornea is focused
equally on all planes, or in all directions.
In astigmatism, the front surface of the cornea is
curved more in one direction than in the other. This
abnormality may result in vision that is much like
looking into a distorted, wavy mirror.
The distortion results because of inability of the eye to
focus light rays to a point.
If the corneal surface has a high degree of
variation in its curvature, light refraction may be
impaired to the degree that corrective lenses are
needed to help focus light rays better.
At any time, only a small proportion of the rays
are focused and the remainder are not, so that
the image formed is always blurred.
Usually, astigmatism causes blurred vision at all
distances. Some people with very high degrees
of astigmatism may have cornea problems such
Distortion or blurring of images at all
Headache and fatigue
Squinting and eye discomfort or irritation
Aphakia & Pseudophakia