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The first progressive addition lens

Varilux

Varilux, the first progressive addition lens in

1959

A forerunner of Essilor, engineered a way to commercially produce progressive lenses.

Bernard Maitenaz of Essel

Which have only two zones of vision and a sharp line marking the border between them

Bifocal lenses

Have many reference points

Progressive lenses

The reference point at which the design's fitting cross is placed. The com mon orthodoxy is to place the Fitting Point at the center of the eye's pupil while the patient's facial plane is in their natural position, i.e., normal posture.

Fitting Point

These are the lens designer's points of reference for optical calculation and alignment. The ____ is also the point for measuring prism in both an unmounted lens and a finished pair of eyewear.

Major Reference Point (MRP)

Some brands refer to the MRP as the

PRP or Prism Reference Point

These engraved reference points, 34 mm apart, 17 mm each side of the MRP, are used for aligning the progressive lens during finishing, as well as for verifying the correct prescription axis and placement in a pair of finished eyewear.

Alignment Reference Markings

The distance between the Fitting Point and the MRP/Alignment Reference Marks.

Progressive Drop

This value varies between different manufacturers and even different designs within a manufacturer's lens portfolio. It can range from 0 to 6 mm, with 4 mm being the most commonly encountered value.

Progressive Drop

The area outlined for verifying the reading Rx power

Near Reference Point

The area outlined for verifying the distance Rx power, generally located approximately 4 mm above the Fitting Point, providing an area completely free of the progressive power gradient.

Distance Reference Point

The linear distance between the beginning of the power gradient—the Fitting Point—and the target add value, most commonly defined as 85 percent of add power

Corridor Length

Variably classed as either 85, 95 or 100 percent of the prescribed add value, depending on the design. Manufacturers are free to define corridor lengths using either of these target add values

Target Add Value

Experience has shown that a progressive reading area should be a minimum of 4 mm to 5 mm in height. Many traditional short corridor designs may provide as little as 3 to 4 mm, which can result in compromised utility and comfort in the reading and intermediate areas

Minimum Reading Area

The distance from the Fitting Point to the center of the reading area. Depending upon the manufacturer or design, targeting the Minimum Fitting Height can truncate up to half of the available reading area.

Minimum Fitting Height

Frame style, size and shape may dictate an adjustment to your target corridor length to ensure the full reading area is not truncated by the contour of the frame's lower rim. Pupillary distance also places a role here, with narrower PDs more sensitive to being truncated by the upward slope of the frame's nasal eyewire.

Total Frame Height and Contour

Closer ______ require shorter corridors to compensate for the reduced drop of the eye's declination intercept with the lens surface. And vice versa for long ______, which then may need longer corridors.

Vertex Distance

Greater ______ require shorter corridors, and lesser ______ require longer corridors for the same conceptual reason stated above in vertex distance.

Pantoscopic Angle

Every 1-mm increase in corridor length will require approximately a 2-degree increase in eye declination.

Rule of thumb

Higher add powers—greater than 2.25D—feature smaller reading and narrower intermediate areas and more surface astigmatism. Therefore, a too short corridor may deliver unacceptable optics because of increased surface astigmatism.

Total Add Power

Total power change seen in a new Rx should be considered for its impact on both distance vision clarity and reading declination. The direction of change, more plus or less plus, is important to factor in as well, regardless of the specific type of ametropia

Rx Delta

Spectacle magnification and prism may impact your corridor choice. The minified and upwardly displaced image in a myopic Rx requires consideration of selecting a shorter value for the corridor. For hyperopic prescriptions, because of image magnification and base up prism, the opposite is true

Ametropic Error

Hyperopic eyes have shorter axial lengths, while myopic eyes feature longer axial lengths. These axial length differences place the center of rotation of hyperopic eyes closer to the cornea, while in myopic eyes the CR further away

Center of Rotation and Dioptric Error

: If base down thinning prism is present, it will upwardly deviate the image at near. In higher adds, this results in a noticeable decrease of the required eye depression angle for the wearer and is important to keep in mind as you determine corridor length.

Prism Thinning

The basic design priority of the lens, i.e., whether the distance, intermediate or reading area has been targeted to be most important, can further impact your corridor value calculation.

Lens Design Priority

Traditional progressives have featured a linear slope of increasing power. Newer, special designs, optimized for computer and users of mobile devices, deliver a non-linear corridor power gradient, with the top portion of the corridor featuring a faster increase in power.

Non-Linear Progressive Power Gradient

Some wearer's may complain these designs intrude on their DV acuity when they are switching from a traditional or balanced design. Compounding factors here include patient posture and the amount and direction of the prescription change

Non-Linear Progressive Power Gradient

Allow the ECP to adjust the corridor length as they desire.

Variable Corridor Designs

Fixed designs are used when prioritizing the size of the reading zone and/or the amount of eye declination required to reach the target add power.

Fixed Corridor Designs

Bifocal wearers, fitted with segments set 8 mm to 9 mm below pupil, are well-suited to using a 10 mm to 12 mm corridor referenced to a 95 to 100 percent target add value.

Fitting pearl

The primary gaze angle of the eye looking straight is generally referenced to the facial plane, defined as the line that connects the brow, upper and lower orbital bones and the jaw.

DISTANCE VISION GAZE

The typical gaze angles for comfortable reading range from 25 to 32 degrees, with the average value assumed to be 30 degrees

READING VISION GAZE

This range corresponds to an area on the spectacle lens between 12.5 mm to 16 mm below the FP, fitted with a pantoscopic tilt of 8 degrees.

READING VISION GAZE

The normal head posture of the wearer

NORMAL POSTURAL HABIT

Depending upon how their current glasses have been measured, fitted or the need for a prescription change, a wearer may have developed a compensatory modification of their normal head posture in order to obtain better acuity for driving, using a computer or for reading.

COMPENSATORY POSTURAL HABIT

Are often used in health care to write medical prescriptions and eyeglass prescriptions

Latin abbreviations

The letters OD stand for

"oculus dexter"

Indicate the right eye.

Indicate the left eye.

Refer to both eyes.

The letters OS stand for

"oculus sinister"

The letters OU stand for

"oculi uterque"

Indicates nearsightedness or farsightedness:

Sphere number

Part of the prescription which measures the degree of astigmatism, representing the difference in curvature and power between two points on the eye, separated by 90 degrees.

Cylinder

Indicates the angle in degrees from 0 to 180, representing the location of the most positive meridian in an eye that has astigmatism when written in minus cylinder form, as in the example above.

Axis

Glasses for distance only

SVD: Single vision distance

Glasses for reading only

SVN: Single vision near

The same power in all meridians

Sphere

A cylinder power corrects astigmatism and represents the difference in the greatest power of the eye and weakest power of the eye, usually separated by 90 degrees.

Cylinder

Indicates the angle (in degrees) between the two meridians of an astigmatic eye

Axis

Distance between the centers of the two pupils between the eyes. This measurement is essential to designing glasses that comfortable to wear and optically perfect.

PD: Pupillary distance

It is usually prescribed to displace the image in a certain direction for patients with crossed-eye (strabismus) or other eye muscle or focusing disorders.

Prism

TNC

TOTAL NEAR CORRECTION

TRP

TOTAL READING POWER

In ___ Feinbloom from Newyork reported a segment bifocal CL and trifocal CL. However, they didn’t come in any clinical purpose as no measures were taken for the rotation of the lens.

1938

In ___ Declare in London, developed simultaneous-vision bifocal which was free from a rotational problem which now has become a basic formula for current bifocal lenses.

1957

In the latter half of the _____,The non-spherical progressive multifocal lens and diffraction progressive contact lens were introduce

1980s and 1990s

When you’re in your 40s, you naturally develop a disease called

Presbyopia

As said by doctors, that there’s no definite logic behind but it is said that with growing age your _____ inside the eye don’t work well andbecome more inflexible.

Ciliary body muscles

Some people need a bifocal lens is because of _____, children develop a condition where they are unable to focus from distance. They also face great fatigue while trying to focus near a distance or while reading or writing in the classroom.

Accommodative dysfunction

You will see in this disease during childhood period, that they start wearing bi-focal lens and this condition is called as

Accommodative Esotropia

It has a small-segment shape like a half-moon or a letter “D” on its side. It is pointed towards the nasal and down toward the bottom.

Flat-top

In this, the round bifocal lens is of 22 or 24mm round segment towards the bottom of the lens. It is developed in a way to make your reading easy and but in today’s times, the round segment is not much used commonly.

Round Segment (Kryptok)

Blended Bifocals

These types of lenses are line bifocal, in which the top half part of the lens is that is used to see distant objects is completely different from the bottom half part that is used to see nearer objects.

Executive Bifocal

These types of lenses are commonly used by corporate people who need to sit on a desk starring computer for hours. But the popularity of these lenses got diminish over time due to unsightly lines present across the lens.

Executive Bifocal

These lenses are invisible in nature, seamless, and have no visible line present on them. While wearing this type of bifocal (multifocal) lens, you will be able to see a gradual increase in transition in reading power as the lens is extended down toward the bottom of the lens without any visible line present to it.

Progressive Lens (FIN)

These lenses got popular in such a short span of time as they gave “speckies” a new different experience.

Progressive Lens (FIN)

When a bi-focal lens is designed with the use of a _____ at the lower half, and the least use of ____ on the upper part.

Convex lens

In the 20thcentury, two lenses are cut in half and combined together, and made a frame out of it.This method of fusing sections of the lens was developed by______at the end of the 19th century.

Louis de Wecker

Will help you to see far objects and close up objects with no middle ground.

Bifocal lens

Is no-line multifocal lenses. In this, as there will not be any visible lines which makes it a better option than bifocal lenses

Progressive lens

Contain two or more lens powers to help you see objects at all distances after you lose the ability to naturally change the focus of your eyes due to age (presbyopia

Multifocal eyeglass lenses

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