Optical Dispensing
An optical dispensing is sub specialty of optometry which includes all procedures from the time the glass prescription is presented to the optician, till the patients are on with the pair the glasses satisfactorily.
HOW TO SELECT FRAMES ACCORDING TO YOUR FACE SHAPE??
There are six face shapes that we observe around the world.
1.Oval Face shape - most common face shape and is considered as an ideal one recommend oversized or rectangular frames
2.Round Face shape - are usually proportional to width and length that features your full cheeks and a broad forehead. recommended rectangular or angular frames for round face shaped persons.
3 .Square Face shape - are characterized by a broad squares forehead and a strong jaw line.We recommended Round or Oval shaped frame.
4. Rectangle face shape - are regarded as the elongated proportion that means a longer, narrower face and nose, along with the same strong jaw line and squares forehead. We recommended round or cat eye shaped.
5.Triangle face shape - have a narrow forehead, but wider cheek. These faces look the best in top heavy styles which help balance out the jaw.
6.Heart face shape have a broad forehead and narrow jaw line or small chin. We recommended deep vertical frame shaped frame.
Frame Measurements Guide
1. Facial wrap - the frame fills properly following the curved line of the face.
Pantascopic Tilt -is the angle between the normal to the temple and frame front.
Vertex distance -is the distance between the front of the cornea and back of the lens.
Spectacles Instrument accessories PD measurement devices
1.PD Ruler Method
Sit directly opposite the patient (arm’s length) . Position yourself 40cm in front of the patient. Eyes are level. Place ruler on the bridge of the patient’s nose Hold pen torch under your left eye directed at the patient’s RE
The dispenser aligns the zero mark of the demo lens with the center of patient’s pupil. The PD for distance is read as the mark falling on the left pupil.
2.The Pupilometer method
Fast and accurate measurement for monocular and binocular PDs. The variation between the visual axes and pupil centre.
Procedure: Hold the instrument in both hands and rest the pupilometer on patients face. Ability to vary working distance from 20cm to infinity Internal hairline moved until line and corneal reflection are coincident .Corneal reflection typically located nasal to pupil center (2 to 5 )
Direct pupillary reflex marking
A pen torch will produce clear corneal reflections. Position yourself 40cm in front of the patient. Eyes are level .Hold a pen light under your left eye, aiming the light at the patient’s eye. Mark the patient corneal reflex in marker.
Lens materials
Glass, plastic, Hi-index etc….
Lens Design
Single vision , Bifocal , Progressive etc
Lens coating
ARC ,UV OR Polarized , Photo chromatic ,Tinted lens
Lens material
Traditionally, people used to prefer glass lenses. But they have become less popular now due to the danger of breaking. They are also heavier in weight than alternatives. These days, CR-39 plastic lenses are the preferred material for spectacle lenses. It is safer, cost effective and offers an outstanding optical quality. some people would be satisfied with just that-a cheap good quality lens which can correct vision.
People become more aware, they’ve started realizing there is more to it than it appears. Like UV protection, even lighter weight.
Lens Coating
Every good lens has 3-4 coatings, Each of a microscopic thickness. Most common of coatings is for toughening the lenses to make it break-resistant. Then UV protection coating and Scratch resistant. Lastly, there is the anti-reflective coating Primarily helps in reducing the effect of reflective light from bright objects such lamps or car headlights at night.
UV Protection and Polarized lens This is one of the major deciding factors. UV exposure has been clinically proven to be an important cause of cataract because of its oxidative effects on humans.
Photo chromatic -A major breakthrough in the area of absorptive lenses took place in 1964 with the invention of corning’s photo gray photo chromatic. These lenses darken when exposed to light. photo chromatics are available in both glass and plastic material.
Tinted lenses -A tint is usually associated with a certain quantity and depth of color, the depth of color is described as density of lens. Both glass and plastic lenses can be tinted to achieve the desired color.
Ophthalmic Lens fitting
Laying off Before a lens is edged it must be marked so that cylinder axis if any is set according to prescription and its optical centre is in correct position relative to lens shape. We use a lensometer to mark three dots indicating optical centre position and the horizontal meridian.
These horizontally placed dots are used to set the lens on correct axis. In case of bifocals and trifocal and trifocals the three dots should be parallel to top of the segment.
Lens cutting
Once the lens is layed off it must now be cut into desired shape.
Lens Edging formers
1. Flat Edge - This is the simple form of edge. It is mainly used for lenses fitted to rimless mounts or as an intermediate stage in the production of other edge forms.
2. Bevel Edge -The bevel edge is used for lenses to be fitted in shall and full rimmed frames. To avoid pressure on the peak of bevel and the attendant risk of chipping the lens.
3.Mini Bevel -The peak of a normal bevel lies approximately midway between the two surfaces with strong minus lenses and high cylindrical power.
4. Grooved Edge - It is simply a flat edge with central groove. Used mainly on lenses fitted to spectacles of the nylon supras or semi rimless types.
5. Hand Edgers - A hand edger is still indispensable piece os equipment although new automatic are being preferred. For starting ensure that the hand edging machine in good working condition. It should be set up with adequate water. Hold the lens is both hands with convex side up. Rest your hands on the dip tray and press the lens against the revolving diamond wheel. Make sure to hold the lens across the wheel and at a slight upward angle. Now slowly rotate the lens passing the grip of lens from hand to hand.
After edging match size of edged lens with the frame. The lens is right when the shape is exactly like that of the frame to be fitted.
