Optics: Presbyopic Optics And Correction Flashcards
Crystalline lens provides approximately ________ the total static refractive power of the eye
1/3rd
Two purposes of the lens:
-combine w cornea to form image on retina
-mechanism for focusing at different lengths
Is the crystalline lens active?
Yes
The lens is ________ in form
Biconvex
What is the diameter of the lens?
9mm
What is the thickness of relaxed lens?
3.6mm
Anterior radius of the lens is ____ times greater than the posterior
1.7
What pattern are the lens fiber cell arranged?
Hexagonal pattern
Diameter, thickness, and weight of the lens at birth
Diameter: 6mm
Thickness: 4mm
Weight: 23-25mg
What is the thickness of the lens as a teenager? Why does this change happen?
3.4mm , the emmetropization process
What is the combined refractive power of the lens?
21.35D
What is the accommodated power of the lens?
31.85 D
What is a cataract?
Any disturbance in the optical homogeneity of the lens
Presbyopia:
The gradual adn progressive age related loss of accommodative amplitude and ultimately due to are related loss in the ability of the lens to undergo accommodative optical changes
Who feels the impacts and symptoms of presbyopia the most?
Emmetrope and uncorrected hyperopes
Accommodative amplitude at age 10 vs age 50
10 D at age 10, 0D at age 55
What happens to the ciliary muscle in presbyopia?
There is a decrease in area and length of the longitudinal and reticular fibers and increase in the area of the circular fibers
Does the ciliary muscle still contract in complete presbyopes?
Yes
Lens ________ increases linearly with age without a systemic increase in lens diameter
Axial thickness
What happens to anterior chamber depth as you get older?
It decreases
What happens to the anterior segment length as you get older?
Increases
Which region of the lens increases its axial thickness more, cortex or nucleus?
Cortex
Changes in the lens with aging:
-accommodation loss
-mass increases
-axial thickness increases
-diameter increases
-anterior surface curvature increases
Phakic eye
Eye with the natural lens
Aphakic eye
Lens without the natural crystalline lens
Pseudophakic eye
Eye contains an intraocular lens
What are the uses for IOLs?
-surgical solution for vision loss due to cataract formation
-continuous vision solution for presbyopia
-accommodating vision or similar to natural crystalline lens
Spherical lens work well only for _______ aperture
Small apertures
Larger apertures generate higher _____________
Spherical aberration
Aspherical lens provides what two things?
-higher image quality
-minimal SA
With higher powers, the lenses become more ___________, even in aspheric lenses
Spherical
What is an A value?
A constant that reflects what the manufacturers have learned about the IOL position
What are monofocal IOL used for?
Restoring vision for one area of focus -> usually distance, reading glasses might still be needed
What is Multifocal IOL used for?
High-quality vision at multiple distances with enhanced vision at distinct distance customized to suit patient lifestyle —> glasses independence
What is an extended depth of focus IOL?
IOLs that provide high quality, continuous vision from near to far and all points in between
Bifocal IOL provides what?
Distant and near vision by dividing the energy between near and far
Ophthalmic diffractive lenses
A zone plate with kinoform shaped grooves
Hybrid lens:
Single refractive lens with a phase plate imbedded on one side of its surfaces
Local grating spacing in diffractive lens design determines the __________
Ray direction (spacing progressively gets smaller from center to edge)
Local step height of diffractive lens design determines the _________________ of light
Diffraction efficiency (how much light put into the add portion)
The image quality of the ADD power is ________ than the base power, meaning….
Less than, visual acuity and energy for near vision is less than the far vision
Multifocal IOL claim to provide decent continuous vision but cause:
-decreased image quality
-unwanted phenomenon like glare or halos
-minimal success
Dysphotopsia:
Unwanted patterns onto the retina that affect the visual performance by obscuring relevant retinal image
Positive dysphotopsia:
Bright artifacts onto the retina
Negative dysphotopsia:
Blockage of light onto the retina
Extended range of vision IOL or depth of focus IOl provides…
Continuous vision and minimizes unwanted phenomena at the same time
What is the holy grail of IOL?
Accommodative IOL
What does the accommodative IOL do?
-mimics the natural lens behavior
-provides additional 1D of vision compared to monofocal lens
What has developed the most effective accommodative-diaccommodative IOL at the preclical level?
Z lens LLC
Glistenings cause __________ which result in a reduction in image contrast
Light scatter
Current challenges in the IOL industry:
-smaller incision (under 2mm)
-posterior capsule opacification (lens epithelial cell growth, can be removed with YAG laser)
