Inroduction
When a patient orders a pair of glasses they first choose a set of frames that suits them. The patient must have a prescription must be written by an optometrist which states the needed lens power and pupil distance (PD). Lenses in the needed power are either ordered or taken from stock. These lenses come from the factory as uncut round blanks approximately four inches across. Edging is the process of cutting these optical lens blanks to fit frames, producing a pair of glasses.
Equipment
There are four pieces of equipment used in the lens edging process. A lensometer is used to check the power in the lens. The tracer is used to determine the dimensions and shape of the frame. The blocker is used to prepare the lens for handling by the edger. The edger cuts the lens to the dimensions specified by the tracer.
Lensometer (Source: Topcon)
Tracer (Source: National Optronics)
Blocker (Source:Topcon)
Edger (Source: National Optronics)
Process
Step 1 Checking the Lens
After receiving the lens blanks the lab technician first checks them visually for any scratches or imperfections that would be cause for rejection. Next using the lensometer the power of the lens is verified. The lens is rotated to the correct axis (lenses with astigmatism or bifocal correction only) and the optical center (point where the prescription is strongest in the lens) and horizontal axis are marked.
Step 2 Tracing the Frame or Pattern
After lens checking the technician must trace the frame. Tracing determines the needed dimensions of the finished lens. There are two methods of doing this, tracing the frame and tracing the lens. The technician determines which method will work best with a particular frame based on experience and the lab's equipment. In frame tracing the demo lenses or the patients old lenses are removed from the frame and the frame is placed face down in the tracer and held in place with specialized clips. In pattern tracing either a pattern of the needed lens shape, a demo lens, or the patients old lens is used. Using a double sided adhesive the pattern or lens is attached to a stand that will hold it in the tracer. The technician will enter relevant information into the tracer such as a job number, patient's name, or other identifying information and also specifies whether he will be tracing a frame or a pattern, and whether he is tracing the right or left side.
There are three parts to the eye exam, the visual acuity exam. This test uses an eye chart to measure how good you can see an object details or the shape of an object at a far distance. 20/20 is the perfect visual acuity and if you 're legally blind than its worse than or equal to 20/200 in both eyes. The second exam is called the slit lamp exam which is a type of microscope that is used to examine the front part of the eye,, that includes the eyelids, conjunctiva, sclera, cornea, iris, anterior chamber, the lens, and part of the retina and optic nerve. The third exam is called dilated exam. Dilated exam is when drops are placed in the eyes to widen or dilate the pupil to enable your eye M.D. to examine the retina and optic nerve for signs of damage (“Diabetic Retinopathy
For an eye to focus correctly on an object, it must be placed in a certain position in front of the eye. The primary focal point is the point along the optical axis where an object can be placed for parallel rays to come from the lens. The secondary focal point is the point along the optical axis where in coming parallel rays are brought into focus. The primary focal point has the object's image at infinity, where as the secondary focal point has the object at infinity. For people who have myopic eyes, the secondary focal point is anterior to the retina in the vitreous. Thus, the object must be moved forward from infinity, in order to be focused on the retina. The far point is determined by the object's distance where light rays focus on the retina while the eye is not accommodating. The far point in the myopic eye is between the cornea and infinity. The near point is determined by which an object will be in focus on the retina when the eye is accommodating. Thus, moving an object closer will cause the perception of the object to blur. The measurement of these refractive errors are in standard units called diopters (D). A diopter is the reciprocal of a distance of the far point in meters (Vander & Gault, 1998). The myopic condition manipulates these variables in order to ultimately make a nearsighted individual.
Simmons, Ashlee. "How Do Glasses Work?" EHow. Demand Media, 28 Oct. 2008. Web. 12 Mar. 2014. Url: http://www.ehow.com/how-does_4564464_glasses-work.html
Myopia is diagnosed with a standard eye exam performed by an optometrist. During a typical exam, an optometrist will place an instrument called a phoropter with a series of lenses in front of your eyes and ask you to identify letters on a distance chart. The exam measures visual acuity, the sharpness or clarity of vision, and is denoted as a fraction such as 20/20. A visual acuity of 20/20 means that you can see what the average person can see when standing 20 feet away from the chart. With information gathered from ...
This is a representation of the eye's lens system. This eye has no eye condition, such as nearsightedness or farsightedness, and the lens is drawn in its relaxed position. The light rays are focused appropriately on the retina. The thickness of the cornea is 0.449 mm, the distance from the cornea to the lens is 2.
The crystalline lens is a double-convex, avascular, transparent membrane-like structure enclosed by a capsule, which is quite malleable, a feature that keeps it under continual tension. As a result of this tension, the lens naturally has an annular contour. The lens is located in the front part of the eye behind the iris and in front of the vitreous body. The lens is held in position by slender suspensory ligaments, also known as zonules. The zonules attach at the equator of the lens like springs and attach the lens to the surrounding ciliary body.
To focus the camera, place the very edge of the aluminum frame guide to what you wish to photograph,
The principle behind the refractive telescopes is the use of two glass lenses (objective lens and eyepiece lens) to gather and bend parallel light rays in a certain way so that the image fits the size of the eye's pupil. Light rays is gather through the opening of the telescope called the aperture and passes through the objective lens and refracts onto a single point called the focal point. From there the light rays continue the same direction until it hits the eyepiece lens which also refract the light back into parallel rays. During the process, the image that enters our eyes is actually reverse of the original image and magnified because the size in which we preceive the image.
The microscope is made up of many parts. The ocular lenses which you use to look through, body tube which is the tube you look through using t...
When the contact lens was invented, the world of vision correction was altered forever. No longer were those people lacking perfect 20/20 vision forced to look any different than everyone else. Both discrete and revolutionary, the contact lens provided a brand new, viable, alternate solution to an age-old problem. After centuries of engineering and discovery the contact lens has evolved greatly. Presently contact lenses are made hard or soft, for daily or continuous wear, gas permeable, and even providing ultraviolet protection. A properly fitted pair of today’s discrete, convenient, versatile, and inexpensive contact lenses provide the best form of vision correction available in today’s market.
All the direct and indirect techniques that are used to produce an image of the
“A dispensing optician’s role entails, advising on, fits, supplying, and recommending the most appropriate spectacles after taking into account a patient’s visual, lifestyle and vocational needs”. (https://www.optical.org/en/Education/Careers/Pre-registration_home.cfm)
...he cornea is deformed so that its surface is oval instead of spherical. Light rays are distorted at the entrance of the eye. This produces a blurred image and is known as astigmatism. To correct it, glasses are given a nonspherical or cylindrical curvature. Cross-eyes and walleyes are produced when both eyes do not work together because of weakness of the eye muscles.