Lynn Lawrence CPOT ABOC Basic Optics Disclaimer Please

Lynn Lawrence, CPOT, ABOC Basic Optics

Disclaimer Please prepare for certification testing with materials from the organization in which you want your certification granted i. e. : AOA JCAHPO ABO NCLE OT

Adnexa: Lacrimal System Lacrimal gland Superior punctum Superior canaliculus Lacrimal sac Excretory ducts Inferior punctum Inferior canaliculus Nasolacrimal duct Nasal cavity

Outline The Visual System Physiology Ametropias Ophthalmic Lenses Properties of Light ▪ UV, Visible, and Infrared Spectrums ▪ Reflection, Refraction, & Absorption ▪ Aberrations Lens Designs ▪ Fitting Basic Optical Formulas

Abbreviations - the following is a listing of accepted abbreviations: ▪ O. D. = right eye ▪ O. S. = left eye ▪ O. U. = both eyes ▪ + = convex, plus ▪ - = concave, minus

The Visual System Eye Movement or ocular motility The eye is connected to the orbit by several muscles which control movement. . . Orbit

$The Visual System There are two main refractive bodies in the human eye. .$

The Visual System There are two main refractive bodies in the human eye. . . Cornea Crystalline Lens

$Vitreous Chamber Functions: Refraction of light Internal support Holds retina in place Spots in$

Vitreous Chamber Functions: Refraction of light Internal support Holds retina in place Spots in vision may be floaters in the vitreous Post vitreous detachment How many chambers are inside the eye?

$The Visual System Cornea The cornea is the primary refractive element in the eye.$

The Visual System Cornea The cornea is the primary refractive element in the eye. . . with a power of around +42 -44 diopters

The Visual System Cornea The tear film maintains both the health and optics of the cornea. . .

Tear Film Layers oil aqueous snot Where does a contact lens rest?

The Visual System Crystalline Lens The crystalline lens has a power of around +12 -18 diopters. . . it is primarily responsible for changing the eye’s focal point…a term referred to as accommodation

The Visual System The retina is the “film” or sensory body. . . Retina

The Visual System Retina Light is converted to electrical impulses which are sent through the optic nerve. . . Fovea . . . the “blind spot” is the point at which the optic nerve connects Macula Optic Disc

Retina – 10 layers Outside of eye Pigment epithelium Rods Cones Outer plexiform layer Horizontal cells Bipolar cells Amacrine cells Inner plexiform layer Ganglion cells Nerve fiber layer Vitreous (inside of eye)

Anatomy / Physiology of the Eyeball 3 Layers Fibrous Layer *Cornea *Sclera Vascular Layer *Choroid *Ciliary body *Iris Nerve Layer *Retina *Macula *Optic nerve What function does each layer have?

Visual Anomalies Ametropias In a “normal” eye, parallel light is brought to a focus on the retina. . . an eye free of refractive error is called “emmetropic”

Visual Anomalies Ametropias An eye with excessive focal power for its length focuses light in front of the retina. . . this refractive error is known as “myopia”

Visual Anomalies Ametropias An eye with insufficient focal power for its length focuses light in front of the retina. . . this refractive error is known as “hyperopia”

$Visual Anomalies Ametropias Another refractive error can occur if every axis is not refracted$

Visual Anomalies Ametropias Another refractive error can occur if every axis is not refracted evenly. . . this refractive error is known as “astigmatism”

Visual Anomalies Ametropias As the eye ages, the crystalline lens loses flexibility. . . this results in a condition known as “presbyopia”

Visual Anomalies Presbyopia The inability to focus on near objects becomes noticeable around age 40 and steadily worsens thereafter. . .

Vision & Ametropias. . . this plus lens may stand alone (NVO) or may work with distance correction (ADD) E E Distance Rx ADD

$Refractive Errors Myopia Hyperopia Astigmatism Presbyopia Amblyopia$

Refractive Errors Myopia Hyperopia Astigmatism Presbyopia Amblyopia

$Emmetropia vs. Ametropia Emmetropia No refractive error Rays of light focus on the retina$

Emmetropia vs. Ametropia Emmetropia No refractive error Rays of light focus on the retina Ametropia An optical error Corrected by glasses, contact lens or refractive surgery

Emmetropic Eye Emma is a perfect woman

Myopia Also called “Nearsighted” Axial myopia Eye is too long Rays of light fall in front of retina Index myopia Diabetes/cataracts Corrected by a concave, or minus lens

Myopic Eye A lens without power is referred to as ______?

$Myopia A refractive condition where parallel light rays focus in front of the retina$

Myopia A refractive condition where parallel light rays focus in front of the retina when the eye is at rest Termed nearsightedness Patient may have 20/20 vision at near, but distance vision will be reduced Corrected with minus lenses

Hyperopia Also called “Farsighted” Axial length of the eye is too short Rays of light fall virtually behind the retina Affected by accommodation Corrected by a convex, or plus lens

Hyperopic Eye The type of lens that corrects for the farsighted condition is called ______?

$Hyperopia A refractive condition where parallel light rays focus behind the retina when the$

Hyperopia A refractive condition where parallel light rays focus behind the retina when the eye is at rest Termed farsightedness Patient may have 20/20 vision at distance and near Corrected with plus lenses

Astigmatism Corneal Astigmatism 2 different points of focus Cornea is “football-shaped” Corrected by cylinder at a specific axis Lenticular Astigmatism Crystalline lens Irregular Astigmatism Cannot be corrected by a lens ▪ Keratoconus ▪ Corneal trauma

Astigmatism A lens that corrects for sphere and cylinder is called _____?

Astigmatism

$Astigmatism A refractive condition where different meridians of the eye have different powers Corrected$

Astigmatism A refractive condition where different meridians of the eye have different powers Corrected by lenses which incorporate cylinder power Usually due to different curvatures of the cornea A lens that corrects for cylinder only ____?

Presbyopia Natural aging of the crystalline lens Affects accommodation Corrected by additional plus power at near Bifocal Trifocal Progressive Reading glasses

Presbyopia A condition in which lost elasticity of the lens leads to the inability to accommodate Age related condition What age does presbyopia normally begin?

$Ophthalmic Lenses Properties of Light Refraction - Dispersion All prisms break white light into$

Ophthalmic Lenses Properties of Light Refraction - Dispersion All prisms break white light into its component colors. . . White Light Dispersed Light . . . this is called dispersion and results in chromatic aberration

$Ophthalmic Lenses Properties of Light Refraction - Dispersion Blue waves are more compact than$

Ophthalmic Lenses Properties of Light Refraction - Dispersion Blue waves are more compact than red waves. . . therefore, they are refracted to a greater degree

$Ophthalmic Lenses Properties of Light Refraction - Dispersion Blue waves are more compact than$

Ophthalmic Lenses Properties of Light Refraction - Dispersion Blue waves are more compact than red waves. . . therefore, they are refracted to a greater degree

Ophthalmic Lenses Properties of Light Absorption A dark lens absorbs light. . .

Ophthalmic Lenses Properties of Light Aberrations The most common aberrations found in ophthalmic lenses are: Power Error Distortion Marginal Astigmatism Chromatic Aberration Unwanted Prism*

$Ophthalmic Lenses Properties of Light Aberrations occur due to various factors: Refractive power Off-axis$

Ophthalmic Lenses Properties of Light Aberrations occur due to various factors: Refractive power Off-axis viewing of objects lens tilt peripheral objects Vertex distance Lens material

Ophthalmic Lenses Properties of Light Aberrations – Power Error Spherical lenses are stronger in the periphery. . .

Ophthalmic Lenses Properties of Light Aberrations – Distortion The result is barrel distortion. . . This is created by a minus lens… . . . the periphery of an object will be minimized to a greater degree than the center

Ophthalmic Lenses Properties of Light Aberrations – Distortion Plus lenses create the opposite effect. . . pincushion effect Aspheric lenses reduce distortion . . . the periphery of an object will be magnified to a greater degree than the center

Ophthalmic Lenses Properties of Light Aberrations – Distortion Compare a spherical lens to an aspheric lens of equal power. . . notice the central curve & thickness

Ophthalmic Lenses Properties of Light Prism Although prism is not technically an aberration, unwanted prism does affect quality of vision. . . the optical center of a lens usually has no prism

Ophthalmic Lenses Properties of Light Prism The eye does not always view objects through the optical center. . . what will the eye perceive?

Ophthalmic Lenses Lens Types There are many types of lenses designed to meet specific patient needs. . . Single Vision Distance Vision Near & Intermediate Vision Bifocals Flat Tops Executive Trifocals Progressive Addition Lenses

Wanted & Unwanted Prism Optical Centers!

Identifying Wanted & Unwanted Prism (cont. ) Light passing thru the OPTICAL CENTER (OC) of a lens is NOT deviated. So, to avoid UNWANTED PRISM, the: Optician needs to measure the patient’s pupillary distance (PD) accurately AND Fabrication lab needs to make the specs so the optical centers (OCs) match the patient’s PD.

Identifying Wanted & Unwanted Prism (cont. )

Identifying Wanted & Unwanted Prism (cont. ) In a perfect world: All eyes would line up perfectly (heterophoria) & no spectacles would ever need prism in them. In a perfect world: Every optician would measure every patient’s PD accurately. In a perfect world: Every lab would make the optical centers (OCs) of every pair of spectacles line up with the patient’s PD so the patient always looked through the OCs of the lenses. Finally, in a perfect world: All glasses would be fit to the patient exactly right.

Ophthalmic Lenses Lens Types – Single Vision lenses have only one focal length. . . single vision lenses can be used to provide clear distance, intermediate, or near vision for presbyopes

Ophthalmic Lenses Lens Types – Single Vision The myopic eye focuses light in front of the retina. . . using a minus powered single vision lens, light is focused on the retina

Ophthalmic Lenses Lens Types – Single Vision “Reading glasses” are also single vision lenses. . . a plus powered single vision lens restores near vision

Ophthalmic Lenses Lens Types – Single Vision Single vision readers only provide clear vision at one working distance. . .

Ophthalmic Lenses Lens Types – Single Vision Single vision lenses require measurement of pupillary distance, and occasionally fitting height. . .

Ophthalmic Lenses Lens Types – Bifocals Bifocal lenses have two focal lengths. . . Distance Near

Ophthalmic Lenses Lens Types – Bifocals For distance vision, the lens contains a “carrier” similar to a single vision lens. . .

Ophthalmic Lenses Lens Types – Bifocals For near vision, an extra “reading” segment is added. . .

Ophthalmic Lenses Lens Types – Bifocals Flat-top bifocals are usually fit: to lower limbus (seg line @ lower lid) decentered 1. 5 mm in from Far PD

Ophthalmic Lenses Lens Types – Bifocals There are several types of bifocals suited to different needs. . . Flat Tops FT 28 FT 35 FT 45 Smart Seg* Curve Top (Cosmolit) Executive (E-Line) Round Seg (Kryptok) Blended

Ophthalmic Lenses Lens Types – Trifocals Trifocal lenses have three focal lengths. . . Distance Intermediate Near . . . generally, the intermediate ADD is 50% of the near ADD

Ophthalmic Lenses Lens Types – Trifocals Objects at the focal length of either the near or intermediate segments are focused on the retina. . .

Ophthalmic Lenses Lens Types – Trifocals Flat-top trifocals are usually fit: to lower edge of the pupil decentered 1. 5 mm in from Far PD

Ophthalmic Lenses Lens Types – Trifocals There are several types of trifocals suited to different needs. . . Flat Tops FTT 7/28 FTT 8/35 Smart Seg* Executive (E-Line) Occupational*

Ophthalmic Lenses Lens Types – Progressives Progressive Addition Lenses (PALs) have an infinite number of focal lengths across a range. . . Distance Intermediates Near

Ophthalmic Lenses Lens Types – Progressives PALs contain a reading ADD that progressively gets stronger- providing many, many focal lengths. . .

Ophthalmic Lenses Lens Types – Progressives are usually fit: at pupil center

Ophthalmic Lenses Lens Types – Progressives PALs require precise fitting if the lens is to perform to its potential, this necessitates: Monocular pupillary distances Verification of fitting height Proper frame adjustment

Ophthalmic Lenses Lens Types – Progressives There are literally hundreds of PAL designs availableeach with unique characteristics. . . Traditional hard design soft design monodesign multidesign Short Corridor Customized Task Specific