NCLE Study Guide

Refracting power of crystalline lens

18 diopters

Refracting power of Cornea

42 diopters

Keratometry (k)

44.00 diopters x 46.00 diopter x 85 horizontal meridian x vertical meridan x axis at 85 degrees Flattest meridan first then the Steepest meridian next. k readings in diopter and millimter. Each 0.05 mm is same as 0.25 diopter 0.05 mm radius equals 2.50 diopters.

Total refracting power of normal eye

60 diopters

Prism ballast

A prismatic shape used in a contact lens to stabilize the lens by preventing rotation.

Detecting contact lens defects

A tear film that begins to break up prior to 10 seconds is a contraindication for contact lens wear. The slit lamp exam may detect many diseases of the eye, including: Clouding of the lens of the eye ( cataract ) Injury to the cornea. Dry eye syndrome. Of particular interest for contact lens (CL) wearers is a detailed examination of the lid margin, paying particular attention to the lids, lashes and tear film. Examine the lashes for signs of blepharitis, madarosis (loss of lashes) and trichiasis (misdirected lashes).

The _____ is the total different in dioptric power between the upper segment and the lower segment. For example: Distance is +1.00 Sph and bifocal measures +3.00 sph The bifocal add is +2.00. Example 2: Distance is -1.00 sph and the bifocal measures +1.00 , the bifocal add is +2.00.

ADD

Curvature of lens chages in order to focus images of objects that are closer to the eye? When ciliary muscles contract and zonules relax, permitting the lens to beome rounder and increase its focusing power.

Accommodation

Light rays are not perfectly focused on the reina due to various refractive errors?

Ametropia

Ophtalmometer (Keratometer)

An instument designed to measure the corneal cuvature by using the cornea s a front surface mirror.

Between the cornea and the iris is a small compartment called ______ _____ , filled with clear, transparent fluid called aqueous humor?

Anterior Chamber

Abrasion

Any break, scratch or area of erosion is considered an abrasion.

Absence of the crystalline lens

Aphakia

Its vital the back surface of lens measurment is exact because if ther is any contact or touch between the conea and the cl then scratch, abrasion or erosion can occur in teh superficial layers of the cornea.

Back surface of lens produces the power of lens

is the curvature of the back surface of the lens. It determines the type of fit the lens must have to match the natural curvature of your eye. It is usually expressed in millimetres and may be further characterised as steep, median, or flat?

Base Curve

The section covering the outer eyeball is called?

Bulbular conjunctiva

Truncation

By cutting off a lower segment of the lens, its roation will be stopped by allowing it to lie along the bottom lid for stability. Consequently the lens can have a torric or cylinder portion ground on its anterior surface. Truncation is useful when combined with prism ballast lenses because it eliminates the heavy, thick edge of the prism that lies below. However, few lens designs today utilize truncation as a design parameter for stabilizing lens orientation.

When proteins of the lens deteriorate, leading to to opacification(clouding) of the lens?

Cataracts

Inner surface of ______ is ciliary processes. These secreat aqueous humor that fills the anterior and posterior chambers.

Ciliary body

Irretation, allergy or infection may cuase the small conjunctival blood vessels to swell makint the conjuntiva appear red is called?

Conjuncrivitis (pink eye)

Thin translucent mucous membrane that lines the inner sruface of the lids and the outer front surface of the eye ball except for the cornea.

Conjunctiva

Provide the focused real & inverted image of the object on the retina. It is composed of a fibrous, jelly like material. This is convex lens that converges light at retina.

Crystalline Lens

Parallel light rays are focused perfectly on the retina?

Emmetropia

The muscles that control movement of the globe are called?

Extraocular Muscles: Medial rectus-rotates eye inward (adduction)

Outer Tunic: Sclera and Cornea?

Fibrous Tunic

Fluorescein

Fluorescein can also appear under the lens in dumbbell shaped patterns.

If drainge of aqueous fluid is impaired, pressure inside the eye rises, increaseing the risk for ______. Increased pressure in the eye can damage the optic nerve, leading to visual field loss and eventually blindness if not approprietly treated.

Glaucoma

The range of front ot back or axial length of the normal eye is 23 and 25 mm in length?

Globe

Cl rests on cornea like paper adheres to wet fingertip by touching it. The natural moisturee on the surface of the cornea is sufiecient enough to create tension and permit he lens to adherer quite strongly.

How Cl rests on the cornea

Farsightedness condition which the cornea and the lens have too little plus power for length of nonaccomidationg eye. Light rays from a distant object come to a focus at a point behind the retina and the image appears blurred.

Hyperopia

The practice of refining the edges?

Intermediate Curve

Controls the amount of light entering the inner part of the eye?

Iris

Irregular astigmatism

Irregular astigmatism is similar to regular astigmatism in that the curvature of the eye's surface is not perfectly round, but where it differs is that instead of the curvature being evenly shaped (mostly in one direction), it is uneven, or curved in multiple directions.

Measurment of a pts corneal curvature. Performed with a device called keratometer or ophthalmomter. Proveds an objective quantitative measurment of corneal astigmatism, measuring the corneal front surface meridians of maximum and minimum curvature as well as designationg the angular direction of these two meridians. Also is helpful in determining the appropriate fit of contact lenses and is an essential measurment before refractive surgery.

Keratometry

Consists of the orbtial structure that produces tears and ducts that drain the excess fluid from the front of the eyes into the nose?

Lacrimal apparatus

This layer is located in the lateral part of the upper lid just under upper oribital rim? The side away from the nose.

Lacrimal gland

Eyelashes Prevent Irritation and Act as Human Whiskers. They operate as dust catchers, protecting the eye from debris that can obstruct vision or cause infection or injury. They are like human whiskers. They act as sensors for objects coming close to the eye—like insects—and trigger a reflexive and protective blink.

Lashes

A thin layer of skin that covers and protects the eye. The eye contains a muscle that retracts the eyelid to "open" the eye either voluntarily or involuntarily. Human ______ contain a row of eyelashes that protect the eye from dust particles, foreign bodies, and perspiration.

Lids

Are oil glands along the edge of the eyelids where the eyelashes are found. These glands make oil that is an important part of the eye's tears. The oily layer is the outside of the tear film that keeps tears from drying up too quickly. A number of eye problems can involve this gland.

Meibomian Glands

Outer layer of the tear film is formed from the oily subtance?

Meibomian glands

There are six extraocular muscles that control all of the movement of the eye. These muscles are?

Muscles: superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, and inferior oblique.

Nearsightedness a condition in which the cornea and lens have too much plus power for the length of eye. Distant objects are focused in front of the retina and thus appear blurred?

Myopia

Inner Tunic: Retina

Neural Tunic

Blue Colbalt Filter with slit lamp

One of the most popular filters used is the blue cobalt filter. This filter is used in conjunction with fluorescein. The blue cobalt filter animates the fluorescein and causes it to radiate to a yellow-green color. This filter along with fluorescein is helpful in identifying abnormalities within the corneal epithelium. The blue cobalt filter is also beneficial in evaluating the fit of gas permeable lenses.

The back surface of the lensin contoured so that it exactly fits the curvature of the cornea. This can be measured by an instument called?

Ophthalmometer or keratometer

only a portion of the lens, which is surrounded by peripheral fitting curves that do not affect vision. It's something like looking out a small window in your house: If you are standing very close to the window, you have a large, unobstructed view of the outdoors.M

Optical zone

Pear-shaped bony cavity in the skill comprising 7 bones that house the glove, the extra ocular muscles, the blood vessels, and the nerves, all of which are cushioned by lyers of fat. Its situated wihing the bony ___ in sucha way that it is protected from major injury by a rim of bone.

Orbit

Is an important test to be performed in the evaluation of glaucoma?

Pachymetry

The Portion of this tissue lining the eyelids is called?

Palpebral conjunctiva

Magnification/Minification

Plus lenses will create magnification which in turn creates a larger than normal retinal image. Minus lenses create minification (negative magnification) which will create a smaller than normal retinal image. Magnification due to the vertex power and vertex distance of a lens is called the POWER FACTOR.

The space between the back of the iris and the front of the vitrious is called?

Posterior Chamber

By age 45, significat amt of lens ability to incrase its curvature is lost and pt is not longer able to focus on very near objects is called?

Presbyopia

Primarily affects near vision and is a normal condition of aging?

Presbyopia

Anterior chamber appears in its normal open position. Resistance to aqueous drainage occurs in the outflow channels betwwen the trabecular meshwork and episcleral blood vessels of the bodys circulation.

Primary open angle glaucoma

In general the existenc of prescribed ____ power in an eyeglass lens is revealed if the lensmeter mires are not centered in teh central portion of lensmeter target, provided that the lens i sbeing measrued at the place on the lens that rests in front of pts pupil.

Prism

Correction with an intracoluar lens (replace lens with surgery)

Pseudophakia

The edge of a ____ contanct lens is thin and polished to that it can gently slide underneath that lid without being dislodged and also prevent lid irritation when blinking

RPG

Rx: OD: +2.00 ADD: +1.00 What is the reading/near power?

Reading/Near power = +3.00

Relative ability of the refractive components of the eye (cornea adn lens) to bring objects into focus on the retina?

Refractive state

Eliminates the cornea as a major source of refractive error of the eye, because it is the same refractive index(RI) as teh fluid in front of it. The fluid interferance between teh contact lens and the cornea fills out irrigularities in the contours of teh anterior corneal surface, converting the cornea to a sphere. Thus fluid may be considered a forward extension of the cornea. If the radius of curvature of the back surface of the contact lens is the same as that of the front surface of the cornea, the refractive power of the contact lens will be the same as that of the cornea. The change in refractive power is produced by altering the curvature of the contact lens, as well as changing the total contact lens power.

Ridgid Contact Lens

White tissue surrounding cornea is a continuation of the fibrous outer lyer that forms the main structural component of the globe, protecting the inraocular contents. This tissue is called?

Sclera

Eye health with slit lamp

Slit lamps are commonly available in emergency departments, and this device is an invaluable tool for the diagnosis and evaluation of common ocular complaints, ocular emergencies, and systemic disease. Although mastery of the slit lamp takes time, basic application to work-up common ocular complaints is a tractable goal for medical students, general practitioners, and emergency medicine providers alike.

One of the conuunctival blood vessesl may rupture, allowing blood to flow under the tissue. May occure after violent coughing or withou explination. Usually resolve in few weeks without treatment and are not a threat to health of eye unless reacure.

Subconjunctival hemorrhages

On the cornea the _____ ______ is made up of three layers: the oily layer on the outside, the watery layer in the middle, and the inner, mucus layer.

Tear film

Slit lamp

The slit lamp is a stereoscopic biomicroscope that emits a focused beam of light with variable height, width, and angle. This unique instrument permits three-dimensional visualization and measurement of the fine anatomy of the adnexa and anterior segment of the eye.

Slit lamp

The standard slit lamp provides a magnification strength of 6x to 40x. This same gentle magnification permits precision viewing of everything from the edge design of a soft contact lens in situ to a visual dissection of the layers of the cornea. In addition, the slit lamp is used to survey the eyes' health, evaluating everything from corneal abrasions to diabetic retinopathy. Not only is the slit lamp a vital tool for eye health evaluation, it is also useful for viewing the ocular adnexa, such as eyelids and lashes.

Fluorescein

Using fluorescein with the biomicroscope is one of the best ways to determine the fit of gas permeable lenses. The process involves applying a moist fluorescein strip to the sclera and then having the patient blink. This distributes the fluorescein dye throughout the tear film and beneath the lens itself. When evaluating fluorescein patterns, the biomicroscope should be set to a diffuse illumination with a cobalt blue filter. As a rule of thumb, the more space between the cornea and the lens itself, the brighter green that the fluorescein will appear. Likewise, less space between the cornea and the lens will produce a dimmer luminescence.

Middle Tunic: Iris, Ciliary body, Choiroid

Vascular Tunic

Astigmatism with the rule

Vertical corneal meridian has teh steepest curvature

What slit lamp does

With the aid of hand-held lenses, the examiner can view the posterior segment as well. A gonioscopic contact lens allows for visualization of iridocorneal angle. The slit lamp is therefore a mainstay of the comprehensive eye examination, allowing optometrists and ophthalmologists to evaluate every anatomical compartment of the eye. However, this instrument should not be relegated to the specialist's toolkit.

Stippling

are fine groups of small pinpoint shaped breaks in the corneal epithelium.

Aberrations

are imperfections of the eye that result in light being unable to focus onto the retina effectively as well as defects in visual image.

Punctate

are larger and more irregularly shaped. Some common reasons for these types of staining patterns are wearing dirty lenses, chemical toxicity or even a poor fit

corneal abrasions

are the result of wearing lenses that are too flat, or from wearing lenses that have deposition or foreign bodies attached

Fluorescein staining patterns

are vital knowledge for contact lens follow-up visits. Any imperfection in the corneal epithelium will have a much brighter glow. Learning the various staining patterns to look out for can help determine the cause of various issues and determine whether the contact lenses are the culprit.

Bitorric

both front and back surfaces are toric

5 layers of cornea?

epithelium bowmans membrane Stroma Descemts membrane Endothelium

Green filter

filter is for viewing vascularization of the cornea. The vessels will appear almost black under the green light. This filter is exceptionally useful when what would otherwise be understated vessels become visible.

Wratten #12 yellow

filter that is used to screen out excessive blue light. It, too, is used in conjunction with fluorescein dye. The Wratten #12 yellow filter will make the fluorescein appear an even-more vibrant green which can be helpful in detecting subtle disruptions.

Back torric

fit is needed when the corneal toricity does not allow a spherical base curve to center properly on the eye.

Dimple veils

have a similar look to stippling stains, but they are essentially indentations in the cornea as opposed to breaks. If dimple veil stains are found in the central zone it may indicate a lens that is too steep. If dimple veiling is in the periphery of the lens, it may indicate a lens that is too flat.

Slit lamp contact fitting

he slit lamp is beneficial while fitting lenses. It enables the fitter to determine if a lens is properly centered, has adequate movement, is fitting too tight, too loose, or riding high, as well as a host of other characteristics.

Front Torric

his lens design is used when there is over 1.25D of prescription cylinder correction with a spherical or near spherical cornea. This lens is ordered with a cylinder power and axis. To prevent the lens from rotating, the lens is ordered with a prism base down to act as weighted ballast or stabilizer.

Astigmatism against the rule

horizontal meridian has the steepest curvature

Sclerotic scatter illumination

is a helpful technique in which the sclera is used as a conduit to send light through the cornea. This is achieved through the process of internal reflection. With this technique, a beam of light 2 to 4 millimeters wide is shone right at the limbus, which in turn brilliantly illuminates the corneal-scleral limbus. The corneal-scleral limbus is the border of the cornea and sclera. Using the sclerotic scatter method is incredibly useful for determining if there are any spots on the cornea that are not transparent. The cornea needs complete transparency as it is the primary refractive medium. Sclerotic scatter also helps detect corneal edema.

keratoconus

is an eye condition in which your cornea — the clear, dome-shaped front of your eye — gets thinner and gradually bulges outward into a cone shape. A cone-shaped cornea causes blurred vision and may cause sensitivity to light and glare. Keratoconus usually affects both eyes.

Visiual field Test

is how wide of an area your eye can see when you focus on a central point. Visual field testing is one way your ophthalmologist measures how much vision you have in either eye, and how much vision loss may have occurred over time.

steep pattern

is indicated when fluorescein pools under the center of the lens. This pattern reveals that the base curve is steeper than K.

flat pattern

is indicated when the fluorescein pools under the outer perimeter of the lens. This pattern reveals that the base curve is flatter than K.

with-the-rule fluorescein pattern

is present when there is with-therule corneal astigmatism. The flatter area of the cornea appears in a dark "dumbbell" shaped pattern along the 180-degree axis.

Direct illumination

is when the beam of light and microscope are fixated directly on the area that is being examined. There are many subclassifications of direct illuminations, each with its own technique and purpose. Learning how and when to use the different illuminations is critical to one's success as an examiner.

Diffuse illumination

is when the light is spread out over the cornea. This is a wider beam of light than a direct illumination would call for. The benefit of a diffuse illumination is that it gives a wonderful view of the entire anterior surface of the eye as well as the eyelids and lashes. Many corneal issues can be viewed with this illumination such as neovascularization and scarring. It is also useful to view contact lenses that are on the cornea; however, without providing much detail. Another common use of a diffuse illumination is to evaluate the tear break-up-time which demonstrates the quality of one's tear film. More often than not, the diffuse illumination is used at the start of the biomicroscopy exam as a starting point to survey the eyes.

Anisometropia

is when the two eyes have a different refractive power (glasses prescription), so there is unequal focus between the two eyes without glasses. This is often due to one eye having a slightly different shape or size from the other causing unequal curving (astigmatism), unequal far-sightedness (hyperopia), or unequal near-sightedness (myopia).

Indirect illumination

it is possible to study anatomical structures adjust the light source itself. With the indirect illumination technique, the beam of light is usually 2 to 3 millimeters wide. One of the most common uses of indirect illumination is the viewing of neovascularization, which is the growth of new blood vessels. Interestingly, the cornea is a living tissue, yet devoid of blood vessels which would impede our vision as light enters through the eye for refraction. The cornea rather receives nourishment through the tear film, vessels that end in loops near the limbus and through the process of deturgesence. With indirect illumination, the examiner is able to observe the growth of new vessels that threaten to invade the cornea. Neovascularization may be a tell-tale sign of over wearing, sleeping in or potentially even ill-fitting lenses.

Sphere

means that the correction for nearsightedness or farsightedness is spherical, equal in all meridians of the eye. indicates the amount of lens power, measured in diopters (D), prescribed to correct nearsightedness or farsightedness.

Retroillumination

the user shines a light on either the iris, crystalline lens or retina, and the microscope is focused on more anterior structures. The bright light that radiates from the more posterior structures creates the perfect backdrop to highlight imperfections of the forward anatomy. One of the most ubiquitous uses of this light illumination technique is to shine light on the iris to examine the cornea. Through the use of retroillumination, one can view deposits within the Descemet's membrane. This technique is also used to observe corneal edema. Edema is synonymous with swelling. As the cornea swells, it changes in refractive power and can cause serious visual issues. Retroillumination is also used for viewing any opacities in the crystalline lens. It is also helpful in the diagnostic process when evaluating cataract formation.

fluorescein

with the biomicroscope is one of the best ways to determine the fit of gas permeable lenses. The process involves applying a moist fluorescein strip to the sclera and then having the patient blink. This distributes the fluorescein dye throughout the tear film and beneath the lens itself. When evaluating fluorescein patterns, the biomicroscope should be set to a diffuse illumination with a cobalt blue filter. As a rule of thumb, the more space between the cornea and the lens itself, the brighter green that the fluorescein will appear. Likewise, less space between the cornea and the lens will produce a dimmer luminescence.

ideal pattern

would be an even distribution of fluorescein behind the lens.This is usually only achieved when a spherical base curve is used on a spherical cornea

against-therule astigmatism pattern

would have the dumbbell going in the opposite vertical meridian, where the 90-degree axis is flatter.