Optical aberrations can impede a person's vision and interfere with diagnostic and medical procedures. Most optical aberrations occur in the cornea and the tear film, with additional contribution from the crystalline lens and marginally from the ocular humours. In the case of dilated pupils, the actual focus spot size on the retina is in the range of 20-100 micrometers, instead of the theoretical range of 1-2 micrometers. This blurs severely the details available to the eye. In addition, the tear film and crystalline lens vary with time, further affecting the spot size.
In addition to affecting a person's eyesight, poor optical conditions can also reduce the effectiveness of eye examinations and treatment. An ophthalmologist examining the eye is restricted to details no finer than the focus spot size. This significantly limits his or her ability to locate early warning signs of abnormalities, diagnose ocular diseases, or perform follow-ups on eye operations. Corneal aberrations also interfere in the examination and treatment of other parts of the eye, such as the aqueous humour and the crystalline lens.
An eye surgeon applying a laser beam to the retina to treat the eye is limited by optical aberrations which result in a large beam spot, thereby causing neighboring areas of the retina to be heated and unnecessarily damaged. And, because of limitations on his or her own view, the surgeon might not even be aware of these damages. These aberrations in the cornea are somewhat reduced by the use of a contact lens attached to the eye with an intervening immersion gel. The device also keeps the lids open during the surgery, but it causes great inconvenience to the patient.
It would therefore be beneficial to have a solution for overcoming the deleterious effects of corneal aberrations on vision, diagnosis, and treatment.
One set of prior art solutions employs some form of scanning in one, two or three dimensions, which enables sequential separation and measurement of the details. This group includes the scanning slit lamp, the scanning laser ophthalmoscope, optical coherence tomography, and acoustic imaging, among others. The optically measuring devices suffer less from the aberrations, but have a limited resolution nevertheless. Another powerful method is adaptive optics, where correction for the ocular aberrations is performed in a servo loop. This method allows direct imaging of the interior of the eye, and in combination with other methods such as mentioned here, even finer scanning of details. It is described by Williams and Liang in U.S. Pat. No. 5,777,719, “METHOD AND APPARATUS FOR IMPROVING VISION AND THE RESOLUTION OF RETINAL IMAGES”. A similar solution for laser surgery is described in U.S. Pat. No. 6,394,999, “LASER EYE SURGERY SYSTEM USING WAVEFRONT SENSOR ANALYSIS TO CONTROL DIGITAL MICROMIRROR DEVICE (DMD) MIRROR PATTERNS” by Williams et al. Unfortunately, all of these methods are rather complicated and the instrumentation takes up large volume. The equipment used is cumbersome, expensive, and many parts of the technology are still immature.
When high resolution is not essential, it is possible to trade it for a very large field. Goniometric devices such as the Abraham or Goldmann objectives were devised in order to gain access to up to 180 degrees in the eye, using up to four mirrors. But the price to be paid is a loss of magnification, and even demagnification of the observed—or laser treated—portions of the retina or the iris. These objectives are placed on the anaesthetized cornea using an immersion gel or fluid, such as methyl cellulose.
A number of prior art references refer to the use of filled goggles. It should be noted that in the context of this disclosure, the word “goggles” refers to a device worn over one or both eyes and comprising an enclosed volume, sealed to the face, which can be filled with a medium such as a liquid or gel, thereby covering all of the eye with the medium. Herbert, in U.S. Pat. No. 4,429,956, “WET CORNEA TELESCOPE”, describes a telescope that has a fluid-filled cell all the way to the cornea for improved optical quality. Herbert (again), in U.S. Pat. No. 4,396,261, “METHOD FOR DETERMINING THE CURVATURE OF A CORNEA”, suggests the use of flat goggles filled with fluid for measurement and calculations for fitting contact lenses. Silverman et al., U.S. Pat. No. 5,776,068, “ULTRASONIC SCANNING OF THE EYE USING A STATIONARY TRANSDUCER”, describe an ultrasonic scanner for the eye, which is attached to liquid-filled goggles for better acoustic contact. Monteleone and Monteleone describe in U.S. Pat. No. 5,927,281, “GOGGLES FOR PREVENTING EXPOSURE KERATITIS”, fluid-filled goggles for maintaining proper environment for eyes with corneal keratitis.
Thomas Young, “On the mechanism of the eye”, Philosophical Transactions of the Royal Society of London vol. 91, 23-88, 1801, and later M. Milodot and J. Sivak, “Contribution of the cornea and the lens to the spherical aberration of the eye”, Vision Research vol. 19, 685-687, 1979, and then P. Artal et al., “Compensation of corneal aberrations by the internal optics in the human eye”, Journal of Vision 1, 1-8, 2001, all show how liquid-filled flat goggles gloss over corneal aberrations in order to separate the optical functions of the cornea and crystalline lens. The largest disadvantage of this method is the need to add very strong positive lenses next to the flat goggles. This is required to further compensate the tens of dioptres of optical power in the cornea itself, lost by its immersion in the fluid. Without this external compensation, the magnifying power of the eye is lost, both for the person wearing the goggles and for the doctor looking into the eye, or operating on it.
It is a main object of the present invention to provide goggles filled with a substance whose refractive index is matched to the refractive index of the cornea, thus reducing the effects of corneal aberrations and tear film variations and improving ocular vision.
Other objects and advantages of the present invention will become apparent after reading the present specification and reviewing the accompanying drawings.