Theme 5: Accommodation and Presbyopia Concept of Accommodation Extent of Accommodation Eye modifications during Accommodation The retinal image and the accommodated eye Variations of the amplitude of accommodation with age: Presbyopia Neutralizing Presbyopia

Concept of Accommodation Acommodation: Eye property for focusing on near objects X’ = X + P The eye focuses by varying its power (P), while in most optical instruments focus is produced by varying the longitude (X’)

Concept of Accommodation - Far Point (fp): Conjugate point with the retina when accommodation is zero - Refraction (R): vergence of the far point Quantifying accommodation

Concept of Accommodation Quantifying accommodation A = R - X R: Refraction X: Vergence of the object

Concept of Accommodation Quantifying Accommodation R = 0  A = -X A = R - X If the eye has refraction zero (R=0, ojo emmetropic eye):

Amplitude of Accommodation Remote Point (fp): Conjugate point with the retina where accommodation is zero. Near Point (np): Conjugate point with the retina when accommodation is maximum.

Amplitude of accommodation Amplitude of Accommodation: Maximum Accommodation

Amplitude of accommodation Range of Accommodation: Distance that separates the far point from the near point

Amplitude of accommodation Range of Accommodation: Distance that separates the far point from the near point Example:

Amplitude of accommodation Range of Accommodation: Distance that seperates the far point from the near point Example

Amplitude of accommodation Clear vision zone (CVZ) and blurry (BVZ)

Amplitude of accommodation Clear vision zone (CVZ) and blurry (BVZ) R=0

Amplitude of Accommodation Amplitude of accommodation for comfortable vision: Maximum value of accommodation that can be used in continuous work. Normally 2/3 is considered the amplitude of accommodation, but this value can be different depending on the author consulted (1/2, 3/4)

Geometric changes in the Iris Geometric changes in the Crystalline Changes in the refraction index Principal modifications of the eye during accomodation: Modifications to the eye during accommodation

Geometric changes to the Iris Decrease of pupil diameter  Decrease circle of defocus if  PE    

Eye modifications during accommodation Geometric changes in the Iris The iris moves forward (A=7D 0.4 mm)

Eye modifications during accommodation Geometric changes in the crystalline A=0DA=7D eLeL 4 mm4.5 mm r 1L 10.2 mm6 mm r 2L -6 mm-5.5 mm

Eye modifications during accommodation Changes in the refractive index A = 0DA = 7D nLnL Intracapsular mechanism of accommodation (Gullstrand)

Eye modifications during accommodation A=0DA=7D Refractive Index Cornea Aqueous Humor Crystalline Vitreous Humor1.336 abscissas (respect to the vertex of the cornea) Sup. posterior cornea0.55 Sup. anterior lens Sup. Posterior lens Radius of curvature Sup. anterior cornea7.8 Sup. posterior cornea6.5 Sup. anterior lens10.26 Sup. posterior lens Le Grand model (A=7D) The theoretical eye accommodated

Eye modifications during accomodation A=0DA=7D Cornea Power42.36 principal object plane-0.06 principal image plane-0.06 Crystalline Power principal object plane principal image plane Complete Eye Power principal object plane principal image plane The theoretical eye accommodated Model Le Grand (A=7D)

The retinal image of the accommodated eye Retinal image of the accommodated eye Retinal image without accommodation The size of the retinal image in the accommodated eye is EQUAL to that in the unaccommodated eye (as long as u is equal and the movement of the principal planes is not considered)

Variations of the range of accommodation with age: Presbyopia With age the capacity of accommodation decreases Am = R- P if emmetropic Am = - P = -1/p If the range of accommodation decreases the near point (p) moves farther from the eye.

Variations of the range of accommodation with age: Presbyopia Presbyopia appears when the near point is farther than the working distance and as a result the eyes are unable to focus on the near objects

Variations of the range of accommodation with age: Presbyopia Am = R- P if emmetropic Am = - P = -1/p Elevated range of accommodation (no presbyopia)

Variations of the range of accommodation with age: Presbyopia Decrease of the range of accommodation with age (presbyopia) Am = R- P if emmetropic Am = - P = -1/p

Variations of the range of accommodation with age: Presbyopia DONDERS Am = 12.5 – 0.2 Age Decrease of the range of accommodation with age Linear variation between 35 and 50 years

Variations of the range of accommodation with age: Presbyopia DUANE Am = 17.1 – 0.3 Year Linear variation between 40 and 55 years Decrease of the range of accommodation with age

Variations of the range of accommodation with age: Presbyopia d w = - 33 cm Am cv = 2/3Am Age at which presbyopia appears For emmetropic eyes R = 0:

Variations of the range of accommodation with age: Presbyopia Age at which presbyopia appears d w = - 33 cm Am cv = 2/3Am

Variations of the range of accommodation with age: Presbyopia DONDERS Am = 12.5 – 0.2 Age 4.5= Age Age=( )/-0.2=40 years Age at which presbyopia appears d w = - 33 cm Am cv = 2/3Am

Variations of the range of accommodation with age: Presbyopia DUANE Am = 17.1 – 0.3 Age 4.5= Age Age=( )/-0.3=42 years Age at which presbyopia appears d w = - 33 cm Am cv = 2/3Am

Optical neutralization of presbyopia Principle of neutralization: Place a lens in front of the eye (which we call addition) that forms the image of an object at the working distance in the near point of the eye (near point and working distance are together)

Optical neutralization of presbyopia Near point and working distance are conjoined through addition X’ = X + P

Optical neutralization of presbyopia For a working distance of 33 cm For a working distance of 25 cm

Optical neutralization of presbyopia far and near Clear vision zone (CVZ) far Clear vision zone (CVZ) Vision zones of a presbyope.

Optical neutralization of presbyopia Near Clear Vision Zone p n is conjoined with np through the addition r n is conjoined with fp through the addition For an emetrope R=0, P=-Am vc

Optical neutralization of presbyopia for Neutralization is possible with Ad Validity of neutralization of presbyopia with an addition for d w =-33cm Ad=3-Am cv

Optical neutralization of presbyopia With the passage of time Am ↓ SOLUTION: An intermediate addition is added so that an intermediate CVZ covers the BVZ generated between fp and fp n A BLURRY VISION ZONE APPEARS

Optical neutralization of presbyopia intermediate Clear Vision Zone p I is the conjugate of p through the intermediate addition r I is the conjugate of r through the intermediate addition For an emmetrope R=0, P=-Am vc :

Optical neutralization of presbyopia - There are diverse values of Ad I that can cover the blurry vision zone that is generated - For a given Ad, the Ad I does not have one unique value. intermediate Clear Vision Zone

Optical neutralization of presbyopia In order for the intermediate zone of clear vision to cover the zone of blurry vision it should meet the following condition intermediate Clear Vision Zone

Optical neutralization of presbyopia intermediate Clear Vision Zone

Optical neutralization of presbyopia For a working distance of 33 cm: intermediate Clear Vision Zone Keeping in mind the relation:

Optical neutralization of presbyopia GRAPHIC SOLUTION For a given Ad, there are diverse values Ad I which allow the zone of blurry vision to be covered intermediate Near Vision Zone

Optical neutralization of presbyopia intermediate Clear vision zone

As can be seen in the graph for Ad  2D, which is to say for Amvc  1D, the neutralization of prebyopia is possible with Ad and Ad I Optical neutralization of presbyopia Vision zones of a presbyope: Validity of the neutralization of presbyopia with an addition

Optical neutralization of presbyopia SOLUTION: PROGRESSIVE LENS Validity of the neutralization of presbyopia with an addition Vision zones of a presbyope: pr = ∞ pp dTdT pr i pp i pr c

Optical neutralization of presbyopia Summary If d T  p presbyopia appears: For d T =-33 cm: Neutralization: For d T =-33 cm: BIFOCAL LENS

Optical neutralization of presbyopia Para d T =-33 cm: Intermediate Addition: TRIFOCAL LENS Summary

Optical neutralization of presbyopia It is not possible to neutralize presbyopia with an addition and an intermediate addition PROGRESSIVE LENS For d T =-33 cm: Summary

Optical neutralization of presbyopia Summary. Vision Zones of the presbyope pr L = ∞ pp L dTdT pr i pp i pr c pr L = ∞ pp L dTdT pr i pp i pr c

Optical neutralization of presbyopia Example Am cv =1D

Optical neutralization of presbyopia Example Am cv =1D