Optician NOCE Practice Test

Changing the curvature of one surface. A lens with a higher angle of curvature will have a shorter focal length because the light waves are refracted at a greater angle with respect to the optical axis of the lens. As the refractive index increases or becomes more curved, the focal length of the lens decreases. Coating the surface of the lens will only change the properties of the surface not the focal length and changing the diameter while keeping the curvature of the surfaces of the lens the same, does not impact the angle of curvature or how light waves are refracted.

A double d lens has a bifocal segment at the top of a lens in addition to a bifocal segment at the bottom of the lens. This allows the wearer to be able to see up close at the top and the bottom of their glasses while allowing them to see distance through the middle. A trifocal lens will allow a wearer to see distance at the top of the lens, intermediate distance through the upper most portion of the segment, and close up at the bottom portion of the segment. A single vision will allow the wearer to see at only one distance through the entire lens, therefore they will not be able to see distance and close up through the same lens. While it is possible to request that the lab make an upside-down bifocal lens, the wearer would only be able to see close up through the top of the lens and distance through the rest of the lens.

While tonometry is performed during an eye examination, it is performed to determine the interocular pressure of the eyes, not to determine the patient's refractive error. A visual field test is performed to determine how well a patient can see objects on the periphery of vision without moving the eyes. Visual acuity is a measurement of the sharpness of one's vision using a projected eye chart to measure the distance visual acuity and a handheld eye chart to measure the near visual acuity. An external examination is performed to the alignment and position of the eyes, and to evaluate the conjunctive, sclera, cornea, iris, pupils, and extraocular movements.

A meniscus lens has one convex and one concave surface. A negative meniscus is thinner at the center than at the edges and a positive meniscus lens is steeper on the convex side making it thicker at the center and thinner on the edges. Meniscus lenses are used for vision correction in both myopic and hyperopic eyes. Biconcave lenses have two concave surfaces and biconvex have two convex surfaces. A plano-convex lens has one flat surface and one convex surface.

The amount of light entering the eye is controlled by the muscles of the iris. These muscles control the size of the pupil, making it larger (dilated) to allow more light in or smaller (constricted) to restrict the amount of light entering. Under low light conditions, the iris opens making the pupil larger and they constrict in bright light conditions. The crystalline lens is located posterior to the iris and is made up of mostly proteins producing one third of the eye's natural power and focuses light into an image on the retina. In the center of the posterior portion of the retina is a small, flat spot called the fovea, which is responsible for high-acuity vision.

A multifocal height is measured from the lower edge of the lens to the center of the pupil. It is always important to adjust the frame to the person before measuring to allow for accurate placement of the multifocal. Taking this measurement from the lower edge of the frame will add extra millimeters to the measurement and cause the multifocal to be placed too high. Measuring to the lower edge of the frame or lens will most likely cause the multifocal to be set too low. 

The absence of the crystalline lens is called aphakia. This condition can either be from birth or caused by injury. The crystalline lens is most often removed by an Ophthalmologist during cataract surgery and an artificial lens is put in its place to correct vision. Accommodation refers to the eyes' diminished ability to focus between distances. The presence of a cataract or a refractive error may result in the removal of the crystalline lens during cataract surgery, however, it is not the definition of aphakia. 

Metal frames include materials such as Monel which is a mixture of a broad range of metals and is the most used material to manufacture eyeglass frames. Other metals include titanium and beta-titanium which offer light weight and durable options. Beryllium is a steel-gray metal that is light weight, very strong and flexible and is available in a variety of colors. Zyl is a plastic material that is very cost-effective and extremely light weight. Nylon is a material that is used primarily for sport or performance frames due to its resistance to hot and cold, and are more flexible, yet rigid enough to hold its shape.

The reference marks on a progressive lens will give you the add power of the lens by a number that is indicated just below the reference mark. The shape and style of the reference mark identify the manufacturer of the lens. This is done by cross referencing the symbol in a progressive identifier book. The reference marks also determine the distance reference points on the lens with the help of a layout chart provided by the manufacturer, and also help to determine if there is unwanted prism in the lens.

A memory metal would be the best choice for a child who suffers from a seizure disorder as the frame can be bent numerous times yet keep its original shape. While nylon frames are a good choice for children who play sports as they are highly impact-resistant, nylon frames will still break if bent in half. A metal frame with spring hinges is durable, but the metal property of the frame will not keep the frame from getting repetitively bent which will decrease the overall strength of the frame over time. A drill mount frame would be the worst choice of the ones listed as they are fragile and some have protruding screws in the lens which could cause an injury to the eye.

Distometer. Vertex distance is the distance between the front surface of the cornea and the backside of a corrective lens mounted in a frame to be worn by the patient. Measuring the vertex distance with a distometer for prescriptions greater than 4 diopters ensures the accuracy of the necessary power. When plus lenses are moved toward the eye, perceived power is lost; when moved away from the eye, perceived power is gained. For minus lenses, it is the opposite: when lenses move toward the eye, perceived power is gained and when they move away from the eye, perceived power is lost. A lensometer is an instrument used in dispensaries to determine the diopter powers of a lens. A vertometer also measures the diopter power of a lens but is more precise and is used in laboratories to locate and mark the optical center of a lens for edging and mounting. A polariscope is used during the lens inspection process to detect stresses or defects in different types of lens materials.

False - Mono meaning one, makes this confusing, however a monocular pupillary distance means each eye is assessed separately, resulting in two numbers, one for each eye. When a binocular pupillary distance is taken, the PD for each eye is added together, resulting in one number.

Most pilots prefer a gray green lens in their sunglasses because it does not distort other colors, and on hazy or cloudy days, the gray green combination color enhances contrast. While orange lenses may distort other colors, they are great for indoor sports like basketball or volleyball where there are lower lighting conditions. Orange lenses also provide increased depth perception. Brown and gray lenses are what you will find in most standard sunglasses for everyday use such as driving or sight-seeing because they reduce a lot of glare.