Introduction:
Dry eye disease affects about 12 million people in the US.
In the human eye, the precorneal tear film covering ocular surfaces is composed of three primary layers: the mucin layer, the aqueous layer and the lipid layer. Each layer plays a role in the protection and lubricaiton of teh eye and thus affects dryness of the eye or lack thereof. Dryness of the eye is a recognized ocular diasese, which is referred to as “dry eye” or “dry eye syndrome” or “keratonjunctivitis sicca (KCS”). Korb (US 2013/0308095)
Dry eye can cause symptoms, such as itchiness, buring, and irritation, which can result in discomfort.
The integrity of the tear film lipid and aqueous layers is critical for proper tear film function and avoidance of dry eye.
Definitions:
Cornea: is a transparent front part of the eye that covers an iris, a pupil, and an anterior chamber that is disposed in front of the lens. Light passes through the transparent cornea and then through the pupil to fall upon a retina that senses the passed light. Together, the retina and a brain produce vision. There is a correlation between the ocular tear film layer thicknesses and dry eye disease. Korb (US 2013/0308095)
The function of the eye can be affected by aberrations to teh shape of the cornea. Thus, clinical diagnosis of vision will benefit from capturing and displaying a corneal topography image. In essence, corneal topography is a non-invasive procedure used to determine the shape and integrity of the cornea of the eye. The clinician projects a seris of illuminated rings onto the surface of the cornea. The pattern is reflected back into a computerized camera which analyzes the pattern to generate a topographical map of the cornea. The topographic images are analyzed to determien the health of the eye. For example, cornea topography is used to analyze corneas before and after vision correction surgery and for contact lens fitting. It is known that a contact lens fitting that is too tight interfers with natural tear flow. Thus, it is important to provide a precorneal tear film analysis after a contact lens fitting. Grenon (US 2015/0138505)
Precorneal tear film: covers ocular surfaces and is composed of the following three primary layers:
(1) mucin layer is comprised of many mucines which retain aqueous matter in the middle layer of the tearm film known as the aqeuous layer. Thus the mucus layer is important in that it assists in the retention of aqueous matter on the cornea to provide a protective layer and lubrication.
(2) aqueous layer is the middel layer that comprises the builk of the tear film. The aqueous layer is formed by secretion of aqueous matter by lacrimal glands and accessory tear glands surrounding the ye. The acqueous matter secreted by the lacrimal glands and assessory tear glands is knwon as “tears”. The function of the aqueous layer is to help flush out any dust, debris or foreign objects that may get into the eye as well as to provide protective layer and lubricaiton to the eye to keep it moist and comfortable. Defects that cause a lack of sufficient aqueous matter in the acquous layer are a common cause of dry eye.
(3) lipid layer is the outmost layer of the term film and also aids to prevent dryness of the eye. The lipid layer is comprised of many lipids known as “meibum” or “sebum” that are produced by meibomian glands in upper and lawer eyelids. The outermost lipid layer is very thin, typically less than 250 nanometers (nm). The lipid layer provides a protective coating over the aqueous layer to limit the rate at which the aqueous layer evaportes. Blinking casues the ypper yelid to mall up aqueous matter and lipids as a ter film, thus proming a protective coating over the eye. A highe rate of evaporation of the aqueous layer can cause dryness of the eye. Thus, if the lipid layer is not sufficient to limti the rate of evaporation of the aqueous layer, dryness of the eye may result.
Sclera: provides a structure for teh eye that gives the eye a generally spherical shap. The sclera also gives the major surface portion of the eye its white color. A mammalian eye includes a cornea and sclera.
Diagnosis of Dry Eye:
Measurement of Lipd and Aqueous Layer Thickness:
There is a correlation between the ocular tear film layer thicknesses and dry eye disease. Korb (US 2013/0308095). Accurate and precise determination of lipid and aqueous layer thicknesses are critical for proper diagnosis of dry eye sub categories.
–Optic Interferometry Devices:
Wavelength dependent optical interferometry has been used to simultaneously measure tear film lip and aqueous layer thickness at a single point at the apex of the cornea over a period of time. Such measurements can be used to diagnose sub categories of dry eye from (a) either lipid or aqueous deficiencies or (b) time-profile changes in lipid and aqueous layer thickness after a blink. Huth (US 2013/0141698)
Lipid and aqueous layer thickness calculation methods using interferometry data has been conducted separately. This is due to the large difference in layer thicknesses (aqeuous 1-5 microns; lipd 20-120 nanometers), basing aqueous thickness calculations upon spectral interference oscillations and absnce of spectral oscillations form the lipid layer. Huth (US 2013/0141698)
Korb (US 2013/0308095) discloses apparatuses and methods employed for mreasuring term film layer thickness (TFLT) of the ocular tear film, which includes lipid layer thickness (LLT) and/or aqueous layer thickness (ALT). Ab iaging device is focused on the lipid layer of the tear film to capture optical wave interfence interactions of specularly reflected light from the tear film combined with a background signal(s) in a first image. The imagaging device is focused on the lipid layer of the tearm film to capure a second image containing background signal(s) in the first image. The second image can be substracted form the first image to reduce and/or eliminate background signal(s) in teh first image to produce a resulting image that can be analyzed to measure tear film layer thickness.
Grenon (US 2015/0138505) discloses ocular surface interferometry (OSI) devices, systems, and methods for mesuring a tear film layer thickness (TFLT) of the ocular tear film, including the lipid layer thickness (LLT) and/or the aqueous layer thickness (ALT). The TFLT can be used to diagnose dry eye syndrome (DES). In one embodiment, a control system is configured to spatially modulate light from a multi-wavelenght light source to project a first circular pattern onto the eye such that at least one first portion of the eye receives emititted light and at least one second protion does not, recieving at an imaging device the at least one first image containing at least one first signal, spatially modulate light from the multi-wavelenght light source to project a second circular pattern onto the eye such athat at least one first porition of the ye does not receive the emitted light and at least one second porition of the ye recieves the light and recieving at the imaging device the at least one second image and then subtracting the at elast one second image from the at elast one frist image to generate a resulting image the represents the ocuar property of the eye.
Huth (US 2013/0141698) discloses a method of measuring tear film lipid layer thickness by applying a mathematical method to simultaneous tear film lipid and aqueous layer thicknesses and corneal refractive index calculations form interferometry data. The method includes aligning an eye of the patient with light originating from a light source, measuring light reflectance from the eye, filtering the light reflectance to the mathematical construct and determing a parameter selected form the group of lipid layer thickness, aqueous layer thickness and corneal surface refractive index.