Presbyopia

Prevalence: Presbyopia is a leading cause of visual impairment for near vision in older adults.
Global Impact: Affects over a billion people worldwide.
Regional Data: In the Brazilian Amazon region, presbyopia accounted for 71.8% of near visual impairment cases.

Cause: Progressive decrease in the accommodative capacity of the lens.
Theories:
- Helmholtz’s Theory: Ciliary muscle contraction leads to relaxation of zonules and increased convexity of the anterior lens capsule.
- Schachar’s Theory: Ciliary muscle contraction increases tension in equatorial zonular fibers and relaxes anterior and posterior zonular fibers, resulting in lens shape changes.
- Catenary Theory of Coleman: Ciliary muscle contraction creates a pressure gradient from vitreous to aqueous compartments, steepening the anterior lens capsule.

Age of Onset: Around 40 years.
Economic Impact: Affects the most economically active age group.
Presbyopia Correction Rates: Low in developing nations due to lack of awareness and affordability; even in developed countries, many do not use corrective lenses.
Statistical Data: Near visual impairment noted in 13.6% (US study) and 21.6% among non-indigenous and 34.7% among indigenous Australians (Australian National Eye Health Survey).

Mechanism: Increased stiffness of the crystalline lens.
Clinical Manifestation: Difficulty reading at the usual distance.
Age-Related Changes: Equal stiffness of lens nucleus and cortex around 35-40 years.

Symptoms: Difficulty reading fine print, headaches, delayed focusing, squinting, drowsiness during near work, and need for bright light.
Evaluation Tools: Royal Air Force (RAF) rule to calculate near point of accommodation (NPA).

Method: Subjective evaluation using reading targets and lens adjustments to determine dioptric power needed.

Non-surgical Options:

Spectacles:
- Single Vision Lenses: Cheaper, for near vision only.
- Bifocal Lenses: Corrects for near and distance vision.
- Progressive Lenses: Corrects near, intermediate, and distance vision; more expensive.
Contact Lenses:
- Monovision: Corrects one eye for distance, the other for near.
- Multifocal Contact Lenses: Corrects near, intermediate, and distance vision.

Surgical Options:

Corneal Procedures:
- Monovision with Laser Refractive Correction: Effective but may affect vision quality.
- Conductive Keratoplasty: Corneal collagen shrinkage increases refractive power.
- Intracorneal Inlays: Devices like Kamra inlay increase depth of focus.
Scleral Procedures:
- Scleral Expansion: Implants to restore ciliary muscle function (insufficient data).
Intraocular Implants:
- Phakic Intraocular Lenses: Corrects near and distance vision.
- Clear Lens Extraction: Followed by intraocular lens (IOL) implantation.
- Multifocal and Trifocal IOLs: Better visual acuity at intermediate distances.

Conditions Affecting Near Vision:
- Macular/retinal diseases
- Diseases of the optic nerve
- Posterior subcapsular cataract
- Hypermetropia
- Astigmatism