Chapter 10: Understanding ophthalmic equipment

slit illumination

A slit or diaphragm reduces the illumination. -For focal, high intensity illumination, better results are attained when the slit is directed from a slit-lamp microscope and the fundus is viewed with a contact lens or Hruby lens. *valuable in estimating the level of various areas of the retina

The Hruby lens is: A) a -55.00 diopter lens B) a jeweler's loupe C) a lens for detecting the intraocular pressure D) a lens for viewing Schlemm's canal E) none of the above

A) a -55.00 diopter lens The Hruby lens is a -55.00 diopter lens for viewing the fundus. It is not as good as a fundus contact lens, but it has the advantage that the retina can be examined without placing an instrument on the eye.

The results of an automated refractor are least affected by: A) large pupils B) cataract C) small pupils D) irregular astigmatism E) corneal scarring

A) large pupils Large pupils do not affect the result of the automated refractor. In fact, the opposite is true. Small pupils may yield no information, often because of misalignment.

If the media are opaque, which of the following tests can be used to determine whether an intraocular tumor is present? A) Transillumination B) Ultrasound A- or B-scan C) P-32 D) All of the above E) None of the above

D) All of the above Probably the most widely used test for an intraocular mass when the media are too cloudy to permit direct examination is the B-scan ultrasound. It is precise, easy to perform, and painless. Permanent records can be obtained. The location and type of a retrolental mass can be detected with this method.

An accurate automated refraction result usually is found in: A) a patient with moderate cataract B) improper alignment of the patient's eyes C) high astigmatism (greater than 7.00 diopters) D) macular degneration E) irregular corneal surface

D) macular degeneration Macular degeneration is a dysfunction of the eye's cones. The actual refractive error is not altered, although the vision is markedly reduced centrally. Consequently, the automated refractor usually provides reliable results as far as the refractive finding is concerned.

relative merits of direct and indirect ophthalmoscopes

Direct: permits a greater magnification ( x 15), easier to use with small or undilated pupils, and is mechanically easier to use Indirect: permits binocular vision and depth perception permits a wider field of view of a given area; easier to use in the operating room without contamination, permits indentation of the sclera and thus a better view of the periphery of the fundus, provides more intense illumination , frees the hand for operative manipulation

To incorporate an automated refractor in a practice, one usually does not need to: A) designate a staff person to be responsible for testing B) provide more housing space C) increase the capital cost D) have a maintenance service agreement E) have a large-volume practice

E) have a large-volume practice Automated refractors can be valuable in any type of practice, whether it is small volume or large volume. They can provide a reference point similar to retinoscopy. The cost effectiveness may be questioned if the practice is relatively small, however.

True or false: Automated objective refractors require significant operator skill and time.

False. Automated objective refractors require little skill by the ophthalmic medical assistant. Skill is required when the patient is not aligned properly or moves during the testing procedure.

The radius of curvature of any lens can be measured simply by using a __________________.

Geneva lens measure The disadvantage of this instrument is that the gauges are calibrated for crown glass only. Moreover, the axis of the cylinder is not precisely determined.

duochrome principle

Green is normally focused in front of the retina, whereas red with longer wavelength, is focused behind the retina for the emmetrope. -Green panel clearer: hyperopic -Red panel clearer: myopic

accessory lenses

Include: -an occluder lens -pinhole disc -stenopeic slit -Maddox rod lens -prisms ranging from 0.50 to 6.00 prism diopters -a red glass filter lens

polarized light

Incorporation of two polarizing filters into the optical system, which polarizes the light leaving the ophthalmoscope, minimizes irritating reflections from the patient's cornea. *intensity of illumination has to be greatly increased to compensate for the filtering effect of the two polarizing filters

red light

Red filters diminish the contrast between the retinal blood vessels and the retina. However, melanin pigment, which absorbs red rays, contrasts strongly with the surrounding red fundus. *Valuable in differentiating hemorrhage from pigmented tumors that contain melanin.

Objective refractors may be used to replace ________________.

Retinoscopy The automated refractors can give a beginning prescription for refinement on a subjective basis. This simulates retinoscopy and becomes a starting point for refraction.

The optic disc is best examined with _______________.

The direct ophthalmoscope The direct ophthalmoscope permits greater magnification so that the fine details of cupping of the disc are easily observed with this instrument. The indirect ophthalmoscope offers a wider field of vision, but it is not as good for examining disc detail such as mild cupping, slight pallor, pits or holes, and the growth of delicate new blood vessels off its surface.

aperture discs

The smaller apertures are particularly useful for viewing the fundus through a small pupil, such as that found in glaucoma patients under treatment

True or false: Some automated refractors provide for subjective refinement.

True. Some automated objective refractors have a subjective component in which the assistant will question the patient as to changes in vision. The instrument can add or subtract both sphere and cylinder to refine the prescription. This is considered a subjective refinement.

True or false: In the duochrome test, a near-sighted person sees the letters more clearly on the red panel.

True. Green normally is focused in front of the retina because of its short wavelength. Therefore, a near-sighted person whose entire image is focused in front of the retina would see the letters on the red side more clearly. Red has a longer wavelength and is seen more clearly by the larger eye of the myopic person. The person whose near-sightedness has been overcorrected, however, will see the green letters more clearly. The duochrome test is useful in determining the type and end point of refractive error.

True or false: Trial frames and lenses are better than the phoropter in determining the refractive status of the aphakic person or a person with high plus or minus lenses.

True. It is useful that the correcting lenses and spectacles lens that the aphakic patient and all patients with high plus or minus lenses finally wears are similar with respect to the distance of the lens from the eye and its tilt. With four-drop lenses, trial aphakic spectacles are provided so that the margin of error is minimized. Even without minimal effective diameter (MED) lenses or four-drop lenses, trial frames are still the best way of arriving at the aphakic person's, or those with high-plus or high-minus lenses, final prescription inasmuch as the measurement for vertex distance is more reliable. The Halberg clip is an excellent method for determining the true spectacle correction.

True or false: The Maddox rod is used to dissociate the eyes and prevent them from fusing.

True. This is done by changing the shape and color of the image of one eye. The rod converts a point of light to a linear rod by virtue of cylindric rods that run across it. The red line always runs perpendicular to the axes of the Maddox rod.

True or false: Manual objective refractors require significant operator skill and time.

True. To operate manual objective refractions, a person needs skill and time for the alignment and adjustment steps.

lensmeter

Used to determine: 1) the dioptric vertex power of a lens 2) the axis 3) the optical center of a lens 4) the presence of a prism and the direction of its base -consists of an illuminated target, a holder for the glasses to be measured, an adjustable eyepiece, and an optical system designed to focus on an image in the anterior focal plane of the lens to be measured

C-scan

also available and are used in diagnosing orbital disease -uses a transducer to cover a small aperture -images soft tissue within the span of a corollary plane that is recorded on polaroid positive-negative film *used primarily for optic nerve lesions, especially tumors

ophthalmodynamometer

an instrument designed to measure the pressure in the ophthalmic artery and its parent vessel, the internal carotid artery -used primarily to diagnose conditions resulting in a lower pressure in the main arteries, such as carotid insufficiency, carotid thrombosis, and carotid stenosis *Pressure difference of 20 between the two eyes is considered significant. *1/3 of patients with a diagnosis of stroke are found to have disease of the carotid arteries *Simple, nontraumatic method of detecting cerebrovascular disease

pachymeter

an instrument for measuring the thickness of the cornea and estimating the depth of the anterior chamber

Koeppe contact goniolens

applied to the cornea with the patient in a reclining position and the examiner viewing the angle structures through a handheld gonioscope

red and green letters (projector)

basis of the duochrome test and means of fine-tuning for refraction -half the panel is illuminated in red and half in green

distometer

caliper used to measure the vertex distance -examiner places the fixed arm of the caliper on the closed lid of the eye and the other arm against the back surface of the lens -the separation between the posterior surface of the lens and eyelid is recorded on the mm scale

direct ophthalmoscope

consists fundamentally of a light source, a viewing device, and a reflecting device to channel light into the patient's eye

optokinetic drum

consists of a handle and a drum that can be readily rotated on the handle -covered with alternating white and dark stripes or pictures -the quick, jerky refixation movements the patient has to make in viewing the revolving stripes produce a jerk nystagmus of the patient's eyes *failure to elicit a jerk-nystagmus type of response in one direction often indicates severe and serious neurologic disease

Hertel exophthalmometer

consists of a horizontal calibrated bar with movable carriers at each side

B-scan

consists of a series of these impulses sent out by a moving transducer that are amalgamated into a two-dimensional image -minimizes possible missed areas; gives clearer picture of the underlying pathologic condition -used to detect tumors of the orbit or eye that cannot be identified by any other means, especially choroidal melanomas

Risley's rotary prism

consists of two counterrotating prisms mounted in rings, one in front of the other -these rings are easily rotated in opposite directions by a small thumbscrew -provides a rapid and simple increase in prism power strength so that a deviation may be rapidly adjusted and measured without delay in introducing individual prisms before the eye

ruby laser

creates a heat reaction in the pigment epithelium of the retina, binding the epithelium of the retina to the underlying choroid -aids in the sealing of retinal holes in a retinal detachment when the retina is adjacent to the choroid

spot retinoscope

designed so that the refractionist can look down the center of a slightly diverging beam of light through the pupil of the patient's eye -in the eye with no refractive error, the rays of light come to a focus on a point on the retina and the refractionist sees the whole pupillary area lit with a red glow -With motion: hyperopic -Against motion: myopic

tonometer

designed to measure the intraocular pressure -used in the most important single test in the detection of glaucoma

excimer laser

developed for two specific uses: 1) enhances vision so that combined myopia and astigmatism, or hyperopia and astigmatism, can be eliminated or refractive errors can be significantly reduced 2) removing corneal scars and smoothing out corneal surfaces after surgery for conditions such as pterygium

prism cover test

displace the image of the deviating eye by the use of prisms so that it falls on the macula of that eye

vertex distance

distance from the cornea of the patient's eye to the back surface of the lens inserted into the trial frame, refractor, or glasses

Goldmann three-mirror contact lens

each mirror is inclined at a different angle, thus permitting a view of the periphery of the retina and a view of the ciliary body, as well as the angle structures of the anterior chamber

Halberg and Janelli clips

eliminates the need for measuring vertex distance -designed to accommodate two trial case rings, a sphere and a cylinder

retinoscope

most valuable instrument in determining the refractive error of an eye -useful in determining the total objective refractive error of an eye and may be the only means of assessing refractive error in infants and small children -also useful for the objective estimation of the refractive error in people who cannot read, are learning disabled, are debilitated and uncooperative, and have speech loss

operating goniolens

one side is partially removed to permit access of a goniotomy knife for surgery on the angle structures

automatic refractors

perform retinosocopy; do not produce a refraction from which a pair of glasses should be made -automatic retinoscopic/objective refraction -results obtained with these machines should be refined by subjective refraction

indirect ophthalmoscope

permits the examiner to see more of the retina in one glance than the direct ophthalmoscope allows -permits the examiner to penetrate moderate cataracts and to see retinal detail -patient's eyes must be dilated with a mydriatic agent in order to see clearly -see a real, inverted image -commonly used with a +20.00 diopter lens

computerized corneal topography

precisely analyze the radius of curvature (mm) and corresponding refractive power (D) at thousands of points across the corneal surface -each pair of points is averaged across its respective meridian to yield two K values, which approximate the cornea's central refractive power

projector

provides a means of projecting, on a silver screen test letters and characters that can be used in assessing visual acuity -consists of housing for a bulb, an opening for introduction of different target slides, and a lens system focused on a silver screen

single-sided goniolens

requires rotation to view the complete periphery of the angle of the anterior segment

multiple pinhole disc

serves the same purpose as the pinhole disc, but is an easier device to use because the patient does not have to search for a solitary tiny central hole -if looking through the pinhole disc improves the patient's visual acuity above the uncorrected vision, this is recorded as vision with PH -corrective lenses often improve vision to the level obtained with the pinhole disc

Luedde exophthalmometer

simply a transparent ruler calibrated in mm

A-scan

single-beam, linear wave that is directed in a probing manner to detect interference along is pathway; travels like a beam of light in a straight direction

pinhole disc

small disc with a small central opening that eliminates peripheral rays of light, permitting only the central rays to pass through -permits the examiner to differentiate poor vision caused by refractive errors from poor vision resulting from disease of the eye -generally, vision that can be improved with a pinhole disc usually can be improved by spectacle lenses

children's goniolens

small to conform the small cornea

blue-green light of argon laser

superior to red light of the ruby laser in treating certain blood vessel diseases of the eye because it is absorbed by the red blood pigment -feature of diabetic retinopathy and other retinal conditions such as Eales' disease, in which vessels grow abnormally and bleed easily, and sickle cell anemia

streak retinoscope

the light source is a straight-line filament of the bulb -If the eye is not emmetropic, the area of the retina illuminated becomes a straight line rather than a spot

Krimsky test

the observer notes the position of the corneal reflexes when a small light is shone into the eyes Prisms are then placed before the deviating eye until the position of the reflex in the pupil of the deviating eye is located in the same position as the fixating eye

trial case

tray of lenses and accessories used to determine the refractive error of an eye -lenses are individually marked in the strengths of dioptric power of each lens, as well as in the direction of axis of the cylindric lenses

prisms

triangular or wedge-shaped piece of plastic or glass that has the property of displacing a bundle of light toward the base of the prism; objects displaced toward apex -used in measuring the presence and amount of any tropias or phorias -most commonly used to measure ocular muscle imbalance

cobalt-blue filters

used for fluorescein studies of the fundus

goniolens

used to examine the ciliary body, the periphery of the retina, and the angle structures -normally these areas are inaccessible for direct examination -only method for detecting angle-closure glaucoma, to determine whether the angle is open or closed -value in locating preferential surgical sites of drainage in glaucoma and for evaluating the cause of failure after glaucoma surgery

transilluminator

used when the media are too cloudy to permit inspection of the fundus and the examiner suspects the presence of an intraocular tumor -consists of a handle and a small, narrow tip that contains a heat-free or insulated high-intensity light source *If the light passes over the site of a solid tumor, the brilliance of the glow in the pupillary space will be diminished and an outline of the tumor revealed. *Useful for providing a bright source of illumination for the inspection of the external eye, the lids, and the iris reflex.

red-free light

viewing the fundus with a relatively red-free filter makes the retinal blood vessels appear black and retinal nerve fibers more prominent -macula stands out against the greenish-gray background of the fundus as a golden-yellow patch *valuable for detecting minute superficial hemorrhages, holes in the retina, and early degenerations of the macula

Posner diagnostic

lens for viewing the anterior chamber, consisting of a highly polished, truncate, silver-surfaced pyramid with a plain anterior viewing surface over four mirrors

heterotropia

manifest deviation of the eyes not held in check by fusion

keratometer

measures the central anterior curvature of the cornea -valuable in eye examinations, particularly when measuring corneal astigmatism -consists essentially of a target that is imaged by the cornea and telescoped to observe this image -reveals the corneal curvature in diopters with the variation in curvature (astigmatism) -invaluable in cases of irregular astigmatism, asymmetric astigmatism, oblique astigmatism, conical cornea (keratoconus), and nystagmus

Doppler test

measures the flow of the internal and external carotid arteries directly -less subject than the ophthalmodynamometer to instrumental and operator errors *used for people with central retinal artery occlusions, transient ischemic attacks, and cerebrovascular accidents

Geneva lens measure

measures the radius of curvature of the lens surface and records it in diopters -consists of a dial with a revolving hand and three pins projecting from the instrument -the approximate dioptric power of the lens can be determined by placing the surface of the lens against the pins and then rotating the lens by 90 degrees *calibrated only for crown glass

electrooculography (EOG)

measures the standing potential between the electrically positive cornea and the electrically negative back of the eye -indicates the activity of the RPE and photoreceptor cells *Diffuse or widespread retinal pigment epithelium (RPE) disease is required to significantly affect the response *Always abnormal with the ERG is abnormal

Hruby lens

-55.00 diopter lens constructed to permit the examination of the vitreous body and the fundus of the eye under slit-lamp examination and magnification -pencil of light is directed through the center of the lens toward the posterior portion of the eye

cross cylinder

-consists of a plus and minus cylinder set at right angles to each other, with a handle set midway between the two axes white: axis of plus cylinder red: axis of minus cylinder -refining instrument that determines the exact axis of the astigmatic error and the exact power of the cylinder

refractor/phoropter

-consists of the entire trial set of lenses mounted on a circular wheel so that each lens can be brought before the aperture of the viewing system by merely turning a dial -entire instrument is mounted on a pole or hydraulic stand -available in either plus or minus cylinders, but never both

trial lenses

-designed to fit a standard trial frame -encircled by metal rim for protection

Maddox rod

-group of either red or colorless parallel glass rods that together act as a cylinder -purpose is to dissociate the eyes and prevent them from fusing; accomplishes this by changing the size, shape, and color of a point of light to a line or streak of light so that fusion is impossible -useful in detecting: 1) presence and amount of heterophoria 2) presence and amount of a heterotropia -the grouped, red cylindric rods of the Maddox lens covert a white point source of light into a red line running perpendicular to the axes of the Maddox rod

loose or individual prisms

-made of plastic or glass -supplied in low powers in standard trial lens sets and in a full range of powers in individual prism boxes

electroretinography (ERG)

-the resting potential of the normal retinal axis is measured by a silver disc electrode mounted in a scleral contact lens -reveals disease of either the rod population or the cone population, or both *Total loss of electrical activity can be recorded in siderosis bulbi (retained iron foreign bodies in the eye), in stages of retinitis pigmentosa, and in severe vitamin A deficiency

slit-lamp microscope

-used to illuminate and examine under magnification the anterior segment of the eye -enables the observer to view binocularly the conjunctiva, sclera, cornea, iris, anterior chamber, lens, and anterior portion of the vitreous, and it permits detection of disease in these areas -have an illumination system combined with a microscope set on an instrument table fitted with a head and chin rest 1) narrow beam of light to a narrow slit 2) vary the length of the slit to a small pinpoint of light 3) introduce color filters to provide a green and deep cobalt blue to the beam of light 4) rotate the slit 5) adjust the angle between the slit beam and the microscope's line of sight -provides increased magnification of the cornea and conjunctiva, including the palpebral conjunctiva

Phenylephrine is an excellent mydriatic for dilating pupils. The safest or most commonly used concentration of this drug is ____________.

2.5% Recently deaths have been reported with the use of 10% phenylephrine; this concentration should not be used for routine dilation. The weaker solution should be used routinely. Phenylephrine should not be given to patients with hypertension or active cardiovascular disease. When it is given, care should be taken to occlude the punctum so that minimal drainage into the nose and minimal systemic absorption occur.

trial frames

Bifocals are prescribed by use of the trial frame with lenses because the patient can best judge a comfortable working and reading distance with the head bent and the eyes lowered in a natural reading position. Trial lenses are also used in refraction of aphakic and high-myopic eyes because it is expedient that the correcting lenses and the spectacles that the patient receives approximate each other with reference to their distance from the eye itself. -essentially a frame capable of holding a group of three or four trial lenses for each eye -front surface is marked off in degrees from 0-180

radioactive phosphorus

One test to detect whether an ocular or retroocular tumor is benign or malignant is determination of the radioactive uptake of the tissues. -Certain highly malignant tumors take up and retain certain radioactive elements, particularly radioactive phosphorus (P-32) to a greater extent than do normal tissues.

When an assistant using an automated refractor requires the patient to provide responses to questions, this is considered a _______________ refraction step.

Subjective The word 'subjective' means that the patient who is the subject, has input into the final results.

Automated objective refractors still require _______________ testing.

Subjective Subjective testing is most important after using an automated objective refractor. The refractor provides only the starting point; one must still obtain individual responses to the given refractive finding.

Placido's disc

flat disc on which have been painted alternating black and white rings that encircle a small central round aperture -used in evaluating the regularity of the anterior curvature of the cornea -useful instrument for detecting early stages of keratoconus; would contain considerable distortion in the concentric rings

four-sided goniolens

four mirrors inclined at the same angle, permitting the examiner to view the complete circumference of the angle without rotation of the goniolens

horizontal and vertical prism bars

fused prisms amalgamated into a single bar of gradually increasing strengths -horizontal direction (base in/out) -vertical direction (base up/down) The prism bar is principally used to measure the amplitude or power of fusion.

heterophoria

fusion-free position of the eyes

yttrium aluminum garnet (YAG) laser

good alternative to the invasive surgery of a peripheral iridectomy in producing a hole in the iris -most useful in treating angle-closure glaucoma -laser trabeculoplasty involves using the laser for shrinkage of the trabecular meshwork

fundus contact lens

handheld contact lens inserted onto the anesthetized eye -permits the examination of the fundus of the eye -eliminates the air interface between the lens and the eye and thereby eliminates anomalies of corneal curvature and corneal irregularities

gonioscope

handheld microscope combined with an illuminating system used in conjunction with the goniolens for gonioscopy of the angle structures

dacryocystography/lacrimal scan

imaging techniques that are occasionally used to evaluate the lacrimal outflow system in patients who report persistent tearing DCG: best anatomic test for determining the actual site of obstruction in the lacrimal outflow system; both lower lid puncta are simultaneously intubated and injected with low viscosity oil; serial radiographs are taken during injection lacrimal scan: most physiologic test to date; simulates the passage of tears through the lacrimal excretory passages without invasive instruments; determines whether the tearing is caused by the inability of the lids to promote tear flow into the lacrimal passages or by an obstruction of the outflow system

exophthalmometer

instrument designed to measure the forward protrusion of the eye -provides a method of evaluating and recording the progression and regression of the prominence of an eye caused by disorders such as thyroid disease and tumors of the orbit