Anomalies of accommodation are not uncommon.
These include: (1) Presbyopia, (2) Insufficiency of accommodation, (3) Paralysis of accommodation, and (4) Spasm of accommodation.(last three anomalies discussed in other posts)
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 in this post) 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)
(sorry for the blurred picture )
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:
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.
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 other posts later)
Surgical Treatment of presbyopia is still in infancy
These include: (1) Presbyopia, (2) Insufficiency of accommodation, (3) Paralysis of accommodation, and (4) Spasm of accommodation.(last three anomalies discussed in other posts)
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 in this post) 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)
(sorry for the blurred picture )
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.
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.
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 other posts later)
Surgical Treatment of presbyopia is still in infancy
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