TeleVue DIOPTRX™ Eyesight Astigmatism Correction Lens

The TeleVue DIOPTRX™ Eyesight Astigmatism Correction Lens is an unprecedented achievement for those who use telescopes for visual astronomy, or for other visual applications including Birding and nature watching or panoramic terrestrial observing. DIOPTRX™ is a unique accessory series that installs onto the top of a number of compatible TeleVue eyepieces (listed below) to correct views from a telescope which have would otherwise be distorted or blurred by eyesight astigmatism. Yet another example of why the highly innovative Al Nagler and TeleVue are considered "Santa Claus" to the international astronomy community.

Right: DIOPTRX™ Eyesight Astigmatism Correction Lens (7,698 bytes).

Background: How The Eye Works


A telescope can be thought of as a light funnel gathering light through its lens or mirror aperture, and with an eyepiece funneling light into the eye. The light exiting the eyepiece next passes through the cornea of the eye, the curved transparent spherical lens tissue in the front part of the eye. The cornea is responsible for focusing the light onto the retina which lines the inside rear wall of the eyeball. The cornea will fine adjust the focus of the eye as the lens changes it's shape to allow clear vision both in the distance and for reading.

Left: DIOPTRX™ Eyesight Astigmatism Correction Lens (7,698 bytes).

The Iris is the diaphragm of the eye much like that of a camera lens in purpose. The Iris is the muscular membrane that regulates the intensity of light illuminating the nerve sensors (cones and rods) in the back of the eye. When in low light or dark environments it dilates (opens) to as much as about 8 mm on a healthy adult eye to permit a wider diameter beam of light into the eye. Conversely in response to white light the iris constricts (closes) to as small as about 1.5 mm.

The entrance pupil is the black spot in the center of the iris, this is the opening in the iris through which light passes. Between the cornea and the iris is the anterior chamber filled with vitreous fluid, a clear jelly-like solution. Light passes through the vitreous on it's way to the retina. The retina is lined with light-sensitive sensors (cones and rods) that accumulate the visual signal and then transmit the information through the optic nerve to the brain where the signals are processed. And so by dilating and exposing more sensors to the stimulis, then the Iris causes the eye to compensate with increased area what is lacked in intensity can provide reasonably good views of fainter areas at night.

How The Eye Doesn't Always Work - And Why A DIOPTRX?

Astigmatism is a vision problem that occurs when the cornea does is not formed in a symmetrical spherical shape. Astigmatism may develop as the eye forms in the womb due to factors including inherited genetics and environment. As people age it is likely their vision will change in focus near or distant or both for example, and one may develop astigmatism too. Most people have a slight astigmatism since it is uncommon for the cornea to have developed in a perfectly symmetrical way. It is also possible that over time, some of the detrimental aspects may change in a way that improves vision too.

The astigmatic cornea has become formed rather like the back of a spoon, longer in one direction than another. When the cornea forms such an irregular shape then the image produced at the retina is not clearly focused and the vision is blurred. The degree of astigmatism can be greater or lesser from one eye to another, the degree is quantified in terms "cylinder" or "cylindrical" in increments of ¼ diopter such as 0.25, 0.50, 0.75 and so on. The axis of the elongation is also characterized in degrees (060, 085, 125, 240). In mild cases the eye may adjust the cornea to focus the light adequately, or a person may complain the images are blurred only when observing at certain distances from the target. The person may feel they have tired or dry eyes, or that it is a struggle to focus to read. In severe astigmatism cases the vision is blurred or distorted when looking at an object at all distances, near or distant. Stars when viewed through a telescope are not pinpoints, but streak into elongated blurs. Astigmatism and focus problems can bring on headache and a sense of fatigue.

In many cases of astigmatism the person also has other visual problems such as near or long sightedness. Two-thirds of people with near sightedness (myopia) also have some significant astigmatism.

People who only have near or distant vision problems may use prescription glasses or contact lenses to correct their vision. When using a telescope these people may remove glasses and use the focus control of a telescope to adjust the image into a sharp focus.

People who have astigmatism may also use prescription glasses or contact lenses to correct their vision. In some cases, astigmatism can be corrected by medical procedure which reshapes the cornea - but it may develop again over time too. Unless the astigmatism is introduced only at the extreme edge of the cornea, and is not a problem when using telescopes with small diameter exit pupils, then they have been condemned to use glasses (or weighted contact lenses) when observing with a telescope that was until the introduction in June 2005 of the TeleVue DIOPTRX™.

The DIOPTRX™ Lenses

The DIOPTRX™ glass lens is provided installed in a rotating machined aluminum cell with rubber eye guard. This permits one to attach and lock DIOPTRX™ onto the tops of more than twenty of the Tele Vue long eye-relief eyepieces to achieve the sharpest full-field viewing possible. DIOPTRX™ models are made available in diopter steps, from 0.25 up to 2.50 diopters. Once installed onto the eyepiece DIOPTRX™ is rotated, tuning for the best viewing orientation. A series of engraved letters on the barrel helps to monitor rotational orientation.

Left: DIOPTRX™ Lens installed on TeleVue eyepiece (47,954 bytes).

Each lens is precisely ground and polished. Then the element is multi-coated to reduce the possibility of reflections. Each DIOPTRX™ cell is engraved with the diopter rating so that it is a simple process to choose the DIOPTRX™ model that matches your eyeglass prescription for astigmatism.

Those Who Chose TeleVue Are Again Rewarded

Starting in mid July 2005, we invite you to visit Company Seven's showroom to test drive these lenses. We will have a test chart on hand so that you may check see the improvements provided by the DIOPTRX™ Lens with your own eyes, and you will be assisted with evaluating them to determine which is best for you. Or, if you can not visit the Baltimore - Washington, D.C. region and if you have a valid prescription for eyeglasses, then you may contact our staff and we will help you determine which lens is recommended for you.

Just take a look at how many TeleVue eyepieces DIOPTRX™ are compatible with:

Long Eye-Relief Tele Vue Eyepieces that Accept DIOPTRX
Ethos	13mm
Nagler Type 4	22, 17, 12mm
Nagler Type 5	31, 26mm
Panoptic	41, 35, 27, 22mm
Plössl	55, 40, 32mm
Radian	18, 14, 12, 10, 8, 6, 5, 4, 3mm
With optional adapter	all Nagler Type 6, 19 & 24mm Panoptic, 20mm Nagler Type 5