3 Crystalline Lens Optics Flashcards
The horizontal corneal diameter is the horizontal visible ____ diameter.
The ACC relates to the _____ of the front surface
Iris
Shape
The crystalline lens provides about ___ 3of the total static refractive power of the eye.
Crystalline lens combines with the cornea to form _______ on the retina. It also provides a mechanism for ________ at different distances. Is an active optical element.
It is _______ in form, with diameter about 9mm. When relaxed, 3.6mm thick while the anterior surface radius of lens is about _.7 times that of posterior surface.
One third
Image. Focusing.
Biconvex. 1.7x
The lack of nutrients in the cells of the lens means these cells are metabolically _______. Can transmit light, but cell damage is __________ (think cataract)
Absorbs little to no light, (no pigments)
Lens fibers are too ______ (20microns) to act as diffraction grating
Inactive
Irreversible
Coarse
Calculate the crystalline lens power
Fa=(n’-n)/Ra
Posterior surface:
Fp=(n-n’)/Rp
Fa= 5D
We get an _D difference when we try to calculate the total lens power of the eye. We get 13.3D when it’s actually __.35D. What accounts for this difference?
8D.
21.35
Refractive index of the lens varies from center to edge. It’s a GRIN lens. The difference of the refractive indexes makes up for the +8D missing of optical power!!
The human crystalline lens generates refraction at both anterior and ______ surfaces of lens as well as within. Combined power is __.__D (relaxed), at accommodated state, refraction shifts to __.85D
Posterior.
- 35
- 85
The crystalline lens varies its axial thickens. Relaxed (distance vision) is about _._mm while Accommodated (near vision) is _mm
3.6mm
4mm
The distance between the far and near points is referred to as the ____________ range.
The difference between the vergence of the far and near points is called the ________ of ____________.
Accommodative amplitude monotonically _______ with age.
AA=15-1/4 Age.
So 10yrs old: AA= __.D and 50yrs old: AA=._D
Accommodation
Amplitude of accommodation
Decrease
AA= 15-1/4(10). =12.5D
AA= 15-1/4(50). =2.5D
Calculate the amplitude of accommodation (AA) of an eye with a far point of 1.25m and a near point of 10cm.
Must convert to D!
The vergence of the far point is 1/1.25 = ____ D
The vergence of the near point is 1/0.10 = ____D
The difference is ____ D – _____ D = _____D
Since, Amplitude of Accommodation is the difference between the vergences of the far and near points:
The vergence of the far point is 1/1.25 = 0.8 D
The vergence of the near point is 1/0.10 = 10D
The difference is 10 D – 0.8D = 9.2D
Aging eye:
__________ of both UV and visible WL decrease as you age.
___________ of light happens in both directions, increases after 40rys.
Lens axial ________ increases all throughout life, which decreases anterior chamber depth
_______ radius of curvature (shape) reduces. 16mm-8.3mm
________ radius of curvature (shape) reduces. 8.3mm-7.5mm
__________ diameter increase from 8.5mm-9.9mm
All possible shape changes declines with age!
Transmittance
Scattering
Thickness
Anterior
Posterior
Equatorial
With increasing age, the nucleus _______ and preferentially _______ more light.
Options for aphakic eyes:
______ eye contains natural crystalline lens
_______ eye is without the natural crystalline lens
____________ eye contains and IOL
Least used today to treat are _______. _______ lenses are a better alternative but elderly patients have trouble handling them. ___’s are the BEST and MOST COMMON solution!!
Scatters. Absorbs
Phakic
Aphakic
Psuedophakic
Glasses. Contact. IOL! Intra ocular lenses
Calculate the amplitude of AA of an eye with a far point of 1m and near point of 25cm
AA= 1/1=1. + 1/.25
=3D
Crystalline lens axial thickness increases all throughout life at a rate of ________ per year
13 microns
