| Jackson cross cylinder | |
|---|---|
 Jackson cross cylinder of power +/- 0.50 diopter | |
| Test of | Astigmatism |
| Based on | circle of confusion |
The Jackson cross cylinder (JCC) is an instrument used by ophthalmologists, orthoptists and optometrists in their routine eye examination, particularly in determination of corrective lens power in patients with astigmatism. It is also used for testing near point of the eye.
Jackson cross cylinder is a single low power lens, which is a combination of a plus cylinder and a minus cylinder of equal power with axis perpendicular to each other, with a handle placed between the two axes at 45 degrees. [1] [2] Therefore JCC is a spherocylindrical lens in which the power of the cylinder is double the power of the sphere and of opposite sign e.g. +0.5DS/-1.0DC or +0.25DS/-0.5DC. JCC are available in different powers including +/-1.00, most commonly used are of +/- 0.25 and +/- 0.50. [2] There are dots or lines to indicate axis of minus and plus powers.
The Jackson cross cylinder is used to determine corrective lens power and its axis in patients with astigmatism. It is also used for testing near point of the eye.
Best corrected vision with a spherical lens should be identified before using a Jackson cross cylinder. In case of astigmatism the best vision with a spherical lens is obtained when the circle of confusion is on the retina. [3]
Best corrected vision with a spherical lens should be identified first. The JCC lens is then placed over spherical lens first with the minus-cylinder axis at 180°, and then with the axis at 90°. [4] If there is no difference in vision, repeat the test with JCC lens axis 45° and 135°. [4] If the patient again reports no difference in vision, there is no astigmatism and if there is improvement in either positions cylindrical lens should be tried to correct astigmatism. [4]
Refinement of axis of cylindrical lens in astigmatism correction is done by placing JCC along with corrective lens with the handle parallel to the axis of corrective lens in the trial frame. [2] Handle is rotated so that the minus and plus lens in cross cylinder interchanges. If there is no difference in vision in either position, the axis of corrective lens is correct and if there is difference in vision, axis should be rotated to get a clear vision. Axis should be rotated by 5 degree on better side. [2]
Refinement of power of cylindrical lens in astigmatism correction is done by placing JCC along with corrective lens with the axis of JCC power parallel to the axis of corrective lens in the trial frame. Handle is rotated so that the minus and plus lens in cross cylinder interchanges and if there is no difference in vision in either position, the power of corrective lens is correct and if there is difference in vision, power should be adjusted. [2]
The uniocular and binocular cross cylinder findings at 40 cm give information about near point of accommodation and near addition needed to correct presbyopia. [5]
In 1837, English mathematician and astronomer George Biddell Airy invented the cylindrical lens and used it to correct astigmatism. [6] In 1849, Irish English physicist and mathematician George Stokes invented Stokes lens to diagnose astigmatism. [6] This lens consisted of two cylindrical lenses, one plano-convex and one plano-concave, which be rotated in opposite directions. In 1887 Edward Jackson described the use of modified Stokes' lens in detecting astigmatism, and in 1907 he described the determination of the axis of a correcting cylinder in astigmatism using a cross cylinder. [7] The modified cross cylinder lens with a handle, which he used was later known as Jackson cross cylinder. [8] [5]
A corrective lens is a lens that is typically worn in front of the eye to improve daily vision. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glasses or "spectacles" are worn on the face a short distance in front of the eye. Contact lenses are worn directly on the surface of the eye. Intraocular lenses are surgically implanted most commonly after cataract removal but can be used for purely refractive purposes.
LASIK or Lasik, commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, since it is in the cornea. LASIK surgery is performed by an ophthalmologist who uses a laser or microkeratome to reshape the eye's cornea in order to improve visual acuity. For most people, LASIK provides a long-lasting alternative to eyeglasses or contact lenses.
An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient. If an eye examination indicates that corrective lenses are appropriate, the prescriber generally provides the patient with an eyewear prescription at the conclusion of the exam.
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- (a-) meaning "without" and στίγμα (stigma), "a mark, spot, puncture".
Radial keratotomy (RK) is a refractive surgical procedure to correct myopia (nearsightedness). It was developed in 1974 by Svyatoslav Fyodorov, a Russian ophthalmologist. It has been largely supplanted by newer, more accurate operations, such as photorefractive keratectomy, LASIK, Epi-LASIK and the phakic intraocular lens.
Refractive eye surgery is optional eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea (keratomileusis), lens implantation or lens replacement. The most common methods today use excimer lasers to reshape the curvature of the cornea. Refractive eye surgeries are used to treat common vision disorders such as myopia, hyperopia, presbyopia and astigmatism.
An Intraocular lens (IOL) is a lens implanted in the eye usually as part of a treatment for cataracts or for correcting other vision problems such as short sightedness and long sightedness, a form of refractive surgery. If the natural lens is left in the eye, the IOL is known as phakic, otherwise it is a pseudophakic, or false lens. Both kinds of IOLs are designed to provide the same light-focusing function as the natural crystalline lens. This can be an alternative to LASIK, but LASIK is not an alternative to an IOL for treatment of cataracts.
Refractive error, also known as refraction error, is a problem with focusing light accurately on the retina due to the shape of the eye and or cornea. The most common types of refractive error are near-sightedness, far-sightedness, astigmatism, and presbyopia. Near-sightedness results in far away objects being blurry, far-sightedness and presbyopia result in close objects being blurry, and astigmatism causes objects to appear stretched out or blurry. Other symptoms may include double vision, headaches, and eye strain.
A phoropter or refractor is an ophthalmic testing device. It is commonly used by eye care professionals during an eye examination, and contains different lenses used for refraction of the eye during sight testing, to measure an individual's refractive error and determine their eyeglass prescription. It also is used to measure the patients' phorias and ductions, which are characteristics of binocularity.
An aspheric lens or asphere is a lens whose surface profiles are not portions of a sphere or cylinder. In photography, a lens assembly that includes an aspheric element is often called an aspherical lens.
Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at night. Astigmatism often occurs at birth and can change or develop later in life. If it occurs in early life and is left untreated, it may result in amblyopia.
Aniseikonia is an ocular condition where there is a significant difference in the perceived size of images. It can occur as an overall difference between the two eyes, or as a difference in a particular meridian. If the ocular image size in both eyes are equal, the condition is known as iseikonia.
Emmetropia is the state of vision in which a faraway object at infinity is in sharp focus with the ciliary muscle in a relaxed state. That condition of the normal eye is achieved when the refractive power of the cornea and eye lens and the axial length of the eye balance out, which focuses rays exactly on the retina, resulting in perfectly sharp distance vision. A human eye in a state of emmetropia requires no corrective lenses for distance; the vision scores well on a visual acuity test.
A cylindrical lens is a lens which focuses light into a line instead of a point, as a spherical lens would. The curved face or faces of a cylindrical lens are sections of a cylinder, and focus the image passing through it into a line parallel to intersection of the surface of the lens and a plane tangent to it along the cylinder's axis. The lens converges or diverges the image in the direction perpendicular to this line, and leaves it unaltered in the direction parallel to its cylinder's axis.
A toric lens is a lens with different optical power and focal length in two orientations perpendicular to each other. One of the lens surfaces is shaped like a "cap" from a torus, and the other one is usually spherical. Such a lens behaves like a combination of a spherical lens and a cylindrical lens. Toric lenses are used primarily in eyeglasses, contact lenses and intraocular lenses to correct astigmatism.
The eye, like any other optical system, suffers from a number of specific optical aberrations. The optical quality of the eye is limited by optical aberrations, diffraction and scatter. Correction of spherocylindrical refractive errors has been possible for nearly two centuries following Airy's development of methods to measure and correct ocular astigmatism. It has only recently become possible to measure the aberrations of the eye and with the advent of refractive surgery it might be possible to correct certain types of irregular astigmatism.
Subjective Refraction is a technique to determine the combination of lenses that will provide the best corrected visual acuity (BCVA). It is a clinical examination used by orthoptists, optometrists and ophthalmologists to determine a patient's need for refractive correction, in the form of glasses or contact lenses. The aim is to improve current unaided vision or vision with current glasses. Glasses must also be comfortable visually. The sharpest final refraction is not always the final script the patient wears comfortably.
A trial frame is a tool used by ophthalmic professionals like ophthalmologists and optometrists. It is basically an adjustable spectacle frame with multiple cells, used to hold corrective lenses, and other accessories in subjective refraction and retinoscopy.
Edward Jackson was an American ophthalmologist better known for popularizing retinoscopy in the United States. He also described detecting astigmatism and its correct axis using a cross-cylinder. The modified Stokes lens he made was later known as Jackson's cross-cylinder.
Stokes lens also known as variable power cross cylinder lens is a lens used to diagnose a type of refractive error known as astigmatism.