Presbyopia

Pathophysiology and causes
Presbyopia (eye sight of old age) is not an error of
refraction but a condition of physiological
insufficiency of accommodation leading to a
progressive fall in near vision.

Pathophysiology. To understand the pathophysiology
of presbyopia a working knowledge about
accommodation (as described above) is mandatory.
As we know, in an emmetropic eye far point is infinity
and near point varies with age (being about 7 cm at
the age of 10 years, 25 cm at the age of 40 years and
33 cm at the age of 45 years). Therefore, at the age of
10 years, amplitude of accommodation (A) =100/7
(dioptric power needed to see clearly at near point) -
1/a (dioptric power needed to see clearly at far point)
i.e., A (at age 10) = 14 dioptres; similarly A (at age 40)
100/25= 1/a=4 dioptres.
Since, we usually keep the book at about 25 cm, so
we can read comfortably up to the age of 40 years.
After the age of 40 years, the near point of
accommodation recedes beyond the normal reading
or working range. This condition of failing near vision
due to age-related decrease in the amplitude of
accommodation or increase in punctum proximum
is called presbyopia.

Causes. Decrease in the accommodative power of
crystalline lens with increasing age, leading to
presbyopia, occurs due to:
1. Age-related changes in the lens which include:
Decrease in the elasticity of lens capsule, and
Progressive, increase in size and hardness
(sclerosis) of lens substance which is less easily
moulded.
2. Age related decline in ciliary muscle power may
also contribute in causation of presbyopia.
Causes of premature presbyopia are:
1. Uncorrected hypermetropia.
2. Premature sclerosis of the crystalline lens.
3. General debility causing pre-senile weakness of
ciliary muscle.
4. Chronic simple glaucoma.
Symptoms
1. Difficulty in near vision. Patients usually
complaint of difficulty in reading small prints (to
start with in the evening and in dim light and later
even in good light). Another important complaint
of the patient is difficulty in threading a needle
etc.
2. Asthenopic symptoms due to fatigue of the ciliary
muscle are also complained after reading or doing
any near work.
Treatment
Optical treatment. The treatment of presbyopia is
the prescription of appropriate convex glasses for
near work.
A rough guide for providing presbyopic glasses
in an emmetrope can be made from the age of the
patient.
About +1 DS is required at the age of 40-45
years,
+1.5 DS at 45-50 years, + 2 DS at 50-55 years, and
+2.5 DS at 55-60 years.
However, the presbyopic add should be estimated
individually in each eye in order to determine how
much is necessary to provide a comfortable range.
Basic principles for presbyopic correction are:
1. Always find out refractive error for distance and
first correct it.
2. Find out the presbyopic correction needed in
each eye separately and add it to the distant
correction.
3. Near point should be fixed by taking due
consideration for profession of the patient.
4. The weakest convex lens with which an individual
can see clearly at the near point should be
prescribed, since overcorrection will also result in
asthenopic symptoms.
Presbyopic spectacles may be unifocal, bifocal or
varifocal (see page 44)
Surgical Treatment of presbyopia is still in infancy

Refractive surgery for presbyopia
Refractive surgery for presbyopia, still under trial,
includes :
Monovision LASIK, i.e., one eye is corrected for
distance and other is made slightly near sighted.
Monovision conductive keratoplasty (CK) is
being considered increasingly to correct
presbyopia in one eye. Principle is same as for
correction of hypermetropia (see page 48).
Scleral expansion procedures are being tried,
but results are controversial.
LASIK-PARM i.e., LASIK by Presbyopia Avalos
Rozakis Method is a technique undertrial in which
the shape of the cornea is altered to have two
concentric vision zones that help the presbyopic
patient to focus on near and distant objects.
Bifocal or multifocal or accommodating IOL
implantation after lens extraction especially in
patients with cataract or high refractive errors
correct far as well as near vision.
Monovision with intraocular lenses, i.e.,
correction of one eye for distant vision and other
for near vision with IOL implantation after bilateral
cataract extraction also serves as a solution for
far and near correction.
Anterior ciliary sclerotomy (ACS), with tissue
barriers is currently under trial. With initial
encouraging results, multi-site clinical studies are
planned for the US and Europe to evaluate this
technique.