The ability to focus on objects at varying distances due to an increase in lens dioptric power as a result of altered tension on the zonular plexus attached to the lens capsule

 

Process of Accommodation:

1. LIGHT ENTERS THE EYE

2. REDUCTION OF ZONULAR TENSION

3. ELASTIC LENS ANTERIOR- POSTERIOR THICKNESS INCREASES

4. LENS BECOMES MORE SPHERICAL 

- Due to rise in curvature, which makes refractive power more positive

5. LIGHT CONVERGES ONTO MACULA

6. NEAR OBJECTS SEEN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

• Lens has an increasing refractive index gradient from the outer cortical surface to the nucleus

  • Each successive fibre layer has greater refractive power and so bends light to a greater degree 

 

PRESBYOPIA

• Amplitude of accommodation decreases with age until reaching zero

• Termed as the reduced ability to focus on near objects

• By 50 years, the dioptric power of accommodation decreases to 0.50 dioptres and by 70, there is approximately no lenticular accommodative ability

• Unsure of the underlying cause, but may be due to:

  • Changes in the elasticity of the lens capsule and zonules

  • Stiffening and sclerosis of the nucleus

  • Ciliary muscle dysfunction

 

 

 

 

 

 

 

 

 

 

 

• Method of treatment:

  • Positive lenses:

    • Reading or progressively powered spectacles e.g. bifocals, varifocals.

    • Multifocal contact lenses and intraocular lenses via surgical treatments are also available.