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LDO Review
| Question | Answer |
|---|---|
| What is the refractive index of CR-39? | 1.49 |
| What is the refractive index of Crown Glass? | 1.523 |
| What is the refractive index of Trivex? | 1.53 |
| What is the refractive index of Polycarbonate? | 1.58 |
| Higher the ABBE number, the ________ the material is. | Heavier |
| What is the refractive index's of High Index? | 1.60, 1.67, 1.71, and 1.74 |
| What is the ABBE value for crown glass? | 59 |
| What is the ABBE value of CR-39? | 58 |
| What is the ABBE value of polycarbonate? | 30; very poor optical quality |
| What is the ABBE value of Trivex? | 43 |
| What is ANSI Z87.1 standards for? | occupational or safety glasses |
| What is minimum thickness for safety eye wear? | 3 mm; plus lenses over 3.00 D can have a minimum thickness of 2.5 mm |
| The point on the lens where a ray of light will pass through without any deviation? | Optical Center |
| The point on the lens that equals the amount of prism prescribed, if any? | Major Reference Point |
| The point equal distance from the lens edge? | Geometric Center |
| The point at which a lens is edged? | Mechanical Center |
| An optical unit of measure that describes the deviation of light after it passes through a lens? | Diopter |
| The distance from the back vertex of a lens to the focal point? | Focal length |
| What lens has identical curvature in all meridians? | Spherical lens |
| What lens has unequal curvature in all meridians? | Cylindrical lens |
| In this condition the globe of the eye is too short? | Hyperopia |
| In this condition the globe of the eye is too long? | Myopia |
| This condition causes a Virtual Image on the retina? | Myopia |
| This condition causes a Real Image on the retina? | Hyperopia |
| This lens type has against motion? | Plus lenses |
| This lens type has with motion? | Minus lenses |
| This lens type has scissor motion? | Cylinder lenses |
| What technique is used to show the Rx of an ophthalmic lens in its primary meridians? | Optical cross |
| What is the curve from which all other curves are determined? | Base curve |
| If you flatten the base curve the image gets what? | Smaller |
| If you steepen the curve the image gets what? | Bigger |
| The lens clock is calibrated to what? | 1.53 |
| When light enters a prism it is deviated towards the what? | The base |
| Chromatic aberration is measured by what? | Abbe Value |
| True or False. The higher the abbe value the lower the amount of chromatic aberration. | True |
| The bending of light as it passes obliquely from one medium to another is what? | Refraction |
| What is the speed of light in air? | 186,000 mps |
| What indicates how much the material will refract or bend light as it enter the material from air? | Refractive index |
| What material has a abbe value of 58? | CR-39 |
| What material has a abbe value of 59? | Crown glass |
| What material has a abbe value of 43? | Trivex |
| What is the abbe value of polycarbonate? | 30 |
| If a plus lens is moved away from the face the Rx gets what? | Stronger |
| If a plus lens is moved closer to the face the Rx gets what? | Weaker |
| If a minus lens is moved closer to the face the Rx gets what? | Stronger |
| If a minus lens is moved away from the face the Rx gets what? | Weaker |
| Determining the portion of cylinder power away from the axis is called what? | Oblique Cylinder Power |
| What percent of cyl power is there 90 degrees away from the axis? | 100% |
| How much cyl power is there on the axis? | none |
| What is the most common way to correct for vertical imbalance? | Slab off prism |
| What is used to verify slab off? | Lens Clock |
| What is the formula for prentice rule? | Prism=Diopters x Distance mm/ 10 |
| Where are trifocals measured from? | the bottom of the pupil |
| Where are bifocals measured from? | The lower lid |
| Where are progressives measured from? | center pupil |
| Overexposure to UV light can cause what? | Cataracts and ARMD |
| What type of UV is the most harmful to the eye? | UV-B |
| What type of UV is the least harmful to the eye? | UV-A |
| When an eye is suppressed for too long it results in what? | Amblyopia |
| A FIXED turning of the eye is what? | tropia |
| A TENDENCY for the eye to turn is what? | Phoria |
| OD: +1.00 OS: -1.00. What would this Rx be an example of? | Antimetropia |
| When one eye is markedly stronger than the other? | Anisometropia |
| A condition where the patient sees different image sizes in each eye? | Aniseikonia |
| What are the 5 layers of the cornea in order? | 1.Epithelium 2.Bowman's Membrane 3.Stroma 4.Descemet's membrane 5.Endothelium |
| A thick transparent substance that is mainly water and 2/3 of the eyes volume is what? | The Vitreous |
| One meridian is plano and the other is myopic, Ex PL-2.00x180. | Simple myopic astigmatism |
| One meridian is plano and the other is hyperopic, Ex PL+2.00x180 | Simple hyperopic astigmatism |
| Both meridians are myopic, Ex -2.00-2.00x180 | Compound myopic astigmatism |
| Both meridians are hyperopic, Ex +2.00+2.00x180 | Compund hyperopic astigmatism |
| One meridian is myopic and other is hyperopic, Ex -1.00+2.00x180. | Mixed astigmatism |
| Instrument used to neutralize a lens? | Lensometer |
| How thick is the cornea? | .5mm |
| What regulates the amount of light entering the eye? | Iris |
| What must be adjusted prior to using the lensometer? | The eye piece |
| What type of bifocal can be manufactured as a fused segment? | flat-top |
| according to ANSI standards, when is it important to consider vertex changes? | When the power exceeds +/- 7.00D |
| What is a lens shape called that has one convex surface and one concave surface? | a meniscus lens |
| Where is the optical center located on a round bifocal? | In the geometric center |
| What is the most common intermediate power for trifocal lenses? | 50% of the add power |
| What type of bifocal segment has the least amount of image jump? | Flat-top |
| light rays that originate at a distance point can be described as what? | Parallel |
| What is the focal length of a 2.50D lens? | 40cm |
| What is double vision called? | Diplopia |
| What type of coating allows more light transmission through the lens? | Antireflective coating |
| How do you find total lens power? | Adding the front surface power and the back surface power together. F1+F2=total lens power |
| What is the formula for focal length? | FL=1meter/Diopters or Diopters=1meter/FL |
| How many centimeters are in a meter? | 100cm |
| If a lens has a front surface power of +6.00D and a back surface power of -7.00D. What is the focal length | 100cm |
| Which of the following lenses have NO power in the 90 degree meridian, +1.25-1.25x090 or +1.50-1.50x180? | +1.50-1.50x180 |
| if a lens has a front surface power of +6.50D and a back surface power of -8.00D. What is the total power of the lens? | -1.50 |
| A +10.00D lens is moved 5mm closer to the eye. What new power will be needed to compensate this change in vertex distance? | +10.50D |
| A patient has an Rx of -10.00D and was refracted at 12mm. If he is fit at 7mm what is the effective power of the lens?? | -10.50D |
| Where is the vertex distance measured from? | from the back surface of the lens to the front surface of the cornea |
| If your patient is blind in one eye, what is the best lens material to use in there glasses? | Polycarbonate |
| A minus lens moved up created what type of prism? | Base down prism |
| What type of zyl frame allows the frame to rest entirely on the nose? | saddle |
| How many layers does the retina have? | 10 |
| What is responsible for peripheral and night vision? | Rods |
| What is responsible fore central and color vision? | Cones |
| What is the outer most layer of the eye responsible for protection? | Sclera |
| How many muscles are attached to the eye? | 6 |
| What muscle moves the eye upward? | Superior Rectus |
| What muscle moves the eye downward? | Inferior Rectus |
| What muscle moves the eye nasally? | Medial Rectus |
| What muscle moves the eye temporally? | Lateral Rectus |
| What muscle rotates the eye inward and down? | Superior Oblique |
| What muscle rotates the eye outward and up? | Inferior Oblique |
| What does the Superior Rectus muscle do? | Moves the eye upward |
| What does the Inferior Rectus muscle do? | Moves the eye downward |
| What does the Medial Rectus muscle do? | Moves the eye nasally |
| What does the Lateral Rectus muscle do? | Moves the eye temporally |
| What does the Superior Oblique muscle do? | Rotates the eye inward and down |
| What does the Inferior Oblique muscle do? | Rotates the eye outward and up |
| What is the refractive index of the crystalline lens? | 1.427 |
| What is the clouding of the crystalline lens called? | Cataracts |
| What is known as the silent thief of sight? | Glaucoma |
| What are the colors of the electromagnetic spectrum? | ROYGBIV |
| What are wavelengths measured in? | Nanometers |
| How many millimeters are in a meter? | 1,000mm |
| In the electromagnetic spectrum what is considered visible light? | 380-760nm |
| What colors is the eye most efficient at detecting? | yellow and green(535nm) |
| What type of lens is Bi-Concave? | Minus lens |
| What type of lens is Bi-Convex? | Plus lens |
| The prescription -3.25+4.25x180, can also be written as? | +1.00-4.25x090 |
| In safety glasses how thick do the lenses have to be? | 3mm thick |
| What is the condition in which the crystalline lens is missing from the eye? | Aphakia |
| What is the condition in which the brain suppresses one eye due to disuse? | Amblyopia |
| An object viewed through a prism appears towards the what? | The apex |
| When a lens is placed on a neoprene gasket and a 5/8" steel ball weighing .56oz is dropped from 50 inches is called what? | The drop ball test |
| What are the two ways to increase impact resistance of a lens? | heat treating and chemical tempering |
| How long does the FDA require records to be kept? | 3 years |
| What is it called when a frame front is parallel to the patients face? | orthoscopic tilt |
| What is it called when the lower eye wire is closer to the patients face then the top of the frame? | pantoscopic tilt |
| What is it called when the top of the frame is closer to the patients face then the bottom eyewire? | retroscopic tilt |
| The horizontal distance between the furthest temporal and nasal edges of the lens is known as what? | The A measurement or the eye size |
| The vertical distance between the furthest top and bottom edges of the lens is know as what? | The B measurement |
| The shortest distance between the nasal edges of each lens is known as what? | The DBL |
| Twice the distance from the geometric center of the lens furthest edge of the lens is known as what? | The ED |
| The running distance between the middle of the center barrel screw hole and the end of the temple is what measurement? | Temple length |
| What is the end piece on a frame? | the point where the temple attaches to the chassis |
| What is the basic metal nickel based material called? | Monel |
| What are the benefits of a titanium frame? | light weight, durable, hypo-allergenic, and corrosion resistent |
| What are the benefits of flexon frames? | light weight, hypo-allergenic, and corrosion resistant |
| A steel gray metal, that is a lower cost alternative to titanium and is light weight, strong and flexible? | Beryllium |
| What is the frame material that is used in high end eye wear and is light weight and corrosion resistant? | Aluminum |
| What material is commonly used for sports and performance frames? | Nylon |
| What frame material is nylon-based, hypo-allergenic, and light weight? | Cellulose Acetate |
| What frame material is a cold insert and shrinks or stretches when heated? | Polyamide |
| What frame material has to be heated to 83 degrees celsius to be adjusted? | Optyl |
| What frame material is rigid, strong, light weight and very popular with designers? | carbon fiber |
| A lens has a front surface power of +2.00D and a back surface power of -8.25D. What is the total or corrective power of the lens? | -6.25D |
| Using the prescription -1.00-1.50x90, what is the power of the lens at the 180th meridian? | -2.50D |
| What is the spherical equivalence of the lens +1.00+2.50x090? | +2.25D |
| A lens having one concave and one convex surface is called what? | meniscus lens |
| What lens treatment best reduces glare from water and road surfaces? | Polarized |
| Slab off is used to compensate for differences in induced prism between the eyes caused by what? | Anisometropia |
| Internal lens stress can be detected using what? | a polariscope |
| What is used to measure vertex distance? | Distometer |
| A lensometer reticle is divided in quadrants to measure what? | the direction of prism |
| Who is the private agency that sets commercial and industry standards? | ANSI |
| which lenses are not exempt from drop ball testing? | Aspheric |
| According to ANSI standards, a lens with 0.50D of cyl must have an axis within how many degrees? | 7 degrees |
| What is the corneas refractive index? | 1.37 |
| The rim around the lenses is known as what? | the eyewire |
| the area of the frame front that rests on the nose? | the bridge |
| The outer areas of the frame front where the temples attach is called what? | endpieces |
| What holds the temples to the frame front? | Hinges |
| The place on the temple where it first bends down to go over the ear is called what? | The bend |
| What temple bends down behind the ear and follows the contour of the skull? | Skull temple |
| What temple is practically straight and holds the glasses on by pressure against the head? | Library temple |
| What temple can be bent down around the ear and also straight back on the head? | Convertible temple |
| What temple curves around the ear, following the crotch of the ear where the ear and the head meet and extend to the level of the earlobe? | Riding bow temple |
| What temple is the same shape as the riding bow but is of metal construction? | Comfort Cable temple |
| What type of frame only holds the lenses in place at their nasal edge? | Numont |
| Before the lens has been edged it is called what? | A lens blank |
| What is the lens blank called when it has the correct powers called for in the prescription and only needs to be edged? | Finished |
| What is the lens blank called that has only one side finished and the other still needs to be ground and polished to the correct prescription? | semi-finished |
| Where must the center thickness of a lens be measure from? | the OC |
| According to ANSI standards what is the axis tolerance of a 0.25D cyl power lens? | 14 degrees |
| According to ANSI standards what is the axis tolerance of a 0.50D cyl power lens ? | 7 degrees |
| According to ANSI standards what is the axis tolerance of a 0.75D cyl power lens? | 5 degrees |
| According to ANSI standards what is the axis tolerance of a 1.00D, 1.25D, and 1.50D cyl power lens? | 3 degrees |
| According to ANSI standards what is the axis tolerance of a >or = to 1.75D cyl power? | 2 degrees |
| In a sphere lens what is the error tolerance according to ANSI standards? | 0.12D |
| According to ANSI standards, a cyl power of 2.00D has a power tolerance of what? | 0.13D |
| Accordign to ANSI standards, cylinder powers between 2.25D and 4.50D has a power tolerance of what? | 0.15D |
| How do you find spherical equivalence? | take half the cylinder and add it to the sphere |
| sagittal depth is used for what? | determining lens thickness |
| Moving the optical center of a plus lens downward will produce what type of prism? | base down |
| Moving the optical center of a minus lens down will produce what type of prism? | Base up |
| A prism made from thin flexible material and consists of small rows of equal powered prisms resulting in the same effect of a conventional prism is called what? | Fresnel prism |
| The ABBE value is commonly used to identify what? | Chromatic abberation |
| What type of lens design does not have a spherical lens surface? | Aspheric |
| When is it necessary to use an aspheric lens? | With a high plus or minus lens |
| True or false, you can use an aspheric lens when the prescription has cylinder in it? | False, you would need an atoric lens |
| When should an atoric lens be recommended and why? | when the cyl is 2.00 or higher to improve peripheral vision |
| What type of lens has a central area with the prescribed power surrounded by an outside area of little or no power? | Lenticular |
| what is the inner part of a lenticular lens called? | Aperture |
| what is the outer part of a lenticular lens called? | carrier |
| How do you find the frame PD? | Add the A measurement and the DBL together |
| What does the Uveal tract consist of? | Choroid, Ciliary body, and the Iris |
| What is the dioptric power of the cornea? | +43.00D |
| What is the axial length of the eye? | 24.4mm |
| The fitting cross is how far above the start of the progressive corridor? | 4mm |
| What type of lens has a spherical front surface and a toric back surface? | cylinder lens |
| When the wearer drops the eyes below the OCs of the lens and vertical prismatic effect of unequal values results for the two eyes, the differential prismatic effect induced is referred to as what? | Vertical imbalance |
| What are a few things to help correct vertical imbalance? | contact lenses, dropping the MRP height, fresnel press on prism, and slab off |
| What part of the lab creates the lens power needed? | Surfacing lab |
| What is the finishing department in a lab responsible for? | edging the lens in the frame |
| In order, list the steps in the edging process? | Spotting, Centration, Blocking, then Edging |
| What point should always appear exactly in front of the wearer's pupil? | MRP |
| A lens is to be edged for a frame with an A dimension equal to 48mm and a DBL equal to 18mm. If the wearer has a PD of 60mm, what is the decentration per lens? | 3mm per lens |
| How much decentration per lens is required to correctly position these lenses for edging? A=52 B=49 DBL=16 PD=70 | 1mm out per lens |
| How much decentration per lens is required for an Rx with the following specifications? A=52 B=43 DBL=18 OD PD=32 OD PD=33.5 | OD 3mm in OS 1.5mm in |
| How many rods and cones are there in the eye? | 120 million rods and 6 million cones |
| Aqueous humor is produced by the what? | Ciliary body |
| Light rays pass through a lens and converge at a point 50 cm behind the lens, what is the power? | 2.00D |
| What is the prismatic effect 8 mm below the optical center of a +3.00D lens? | 2.4 Base up |
| A +5.00D lens decentered 2 mm creates how many diopters of prism? | 1.00D |
| A patient wearing 2.00D of prism base up OD and 6.00D base up OS experiences a total prismatic effect of what? | 4.00D base up OS |
| How much prism is generated 8mm from th OC of a +4.00 D lens? | 3.2 prism |
| How far do you decenter a +4.00D lens to create 2 diopter of prism? | 5mm |
| A -4.00 lens must be decentered _____mm to induce 1.00 prism Diopter? | 2.5mm |
| What 4 things affect refraction? | curvature, angle of incidence, thickness, and index of refraction |
| What is snells law used for? | to find index of refraction |
| What is another name for an executive bifocal? | the franklin |
| Where is the OC located on a Franklin bifocal? | on the seg height |
| What type of bifocal has the most amount of image jump? | Ultex |
| What type of bifocal is made of glass and the power in the near is made of a higher index than the carrier? | fused bifocal |
| In a lined bifocal, where is the near OC located? | 5mm below the seg |
| What is another name for slab off? | bi-centric grinding |
| When is it necessary to calculate vertical imbalance? | When the patient has 1.50D of anisometropia |
| For conventional slab off, what type of prism would you order and what lens would you put it in? | Base Up Most Minus |
| For reverse slab off, what type of prism would you order and what lens would you put it in? | Base Down Least Minus |
| What are the steps to calculate slab off? | find the power at 90, prentice rule, then difference between the two prisms. |
| What type of slab off would you use on a glass lens? | conventional slab off |
| What type of slab off would you use on a plastic lens? | Reverse slab off |
| What type of lenses are EXEMPT from the drop ball test? | glass, lenticular, slab off, and raised multifocal |
| When does heat treating not work? | plus or minus 7 diopters |
| What causes the lens to be strong after heat treating? | the molecules tense up and creates tension |
| What happens during chemical tempering? | Exchanging ions, sodium and lithium are replaced by potassium |
| What percent of cyl power is there 60 degrees away from the axis? | 75% |
| What percent of cyl power is there 45 degrees away from the axis? | 50% |
| What percent of cyl power is there 30 degrees away from the axis? | 25% |
Created by:
Kayla Carpenter
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