GB2519056A

GB2519056A - Method of measuring a property of an ocular membrane

Info

Publication number: GB2519056A
Application number: GB1313806.0A
Authority: GB
Inventors: Stephen Morris
Original assignee: Nightingale EOS Ltd
Current assignee: Nightingale EOS Ltd
Priority date: 2013-08-01
Filing date: 2013-08-01
Publication date: 2015-04-15
Also published as: GB201313806D0

Abstract

A method of measuring a property of an ocular membrane, such as thickness, refractive index, curvature, shape, surface orientation or alignment, using Beam Profile Reflectometry (BPR) is provided. The ocular membrane may comprise the cornea, lens or retina of an eye, and the measurement process may be part of a corneal pachymetry procedure. The property may be measured in vivo or in vitro. BPR may be used to sample the membrane as part of a mapping process to form an image of the property across the membrane. Sampling may be performed using a focused laser spot one micron in diameter and configured to scan across the membrane. Also claimed are an apparatus and the use of BPR to measure a property of an ocular membrane.

Description

Method of Measuring a Property of an Ocular Membrane

Field of the Invention

This invention relates to a method of measuring a property of an ocular membrane.

Background to the Invention

Corneal Pachymetry is the term used for the measurement of the thickness of the cornea (the front-most membrane of the eye). This measurement is useful in a number of contexts. For example, in vivo measurements can be useful when characterising the properties of a patient's eye before and after laser eye surgery (e.g. using the LASIK procedure). They can also be helpful in interpreting measurements of intraocular eye pressure (lOP) in the context of diagnosing glaucoma. In vitro measurements can be useful in medical research and also in the process of performing corneal transplants -as a predictor both of the likelihood of successful grafting and the patient's resulting vision prescription post-transplant.

Conventional methods for performing this measurement include ultrasound (which is a contact technique), slit-scan imaging tomography, confocal microscopy and optical coherence tomography. Each of these methods can obtain the thickness of the cornea and, in some cases, the shape of the corneal profile, but none appear to be able to measure the refractive index of the cornea. This is in any case believed to vary as a function of the level of hydration, and to exhibit some amount of non-uniformity throughout the layer thickness.

It is an aim of the present invention to provide an alternative and improved method of measuring a property of an ocular membrane, such as Corneal Pachymetry.

Summary of the Invention

According to a first aspect of the present invention there is provided a method of measuring a property of an ocular membrane using Beam Profile Reflectometry (BPR).

A second aspect of the present invention relates to use of Beam Profile Reflectometry (BPR) in measuring a property of an ocular membrane.

According to a third aspect of the present invention there is provided an apparatus configured for measuring a property of an ocular membrane using Beam Profile Reflectometry (BPR).

The applicants believe that use of BPS in the context of measuring properties of ocular membranes offers significant benefits when compared to conventional techniques such as those described above for Corneal Pachymetry.

Beam Profile Reflectometry (BPS), for example, as described in US 4,999,014, is an established technique for measuring the thicknesses of thin films and coatings deposited upon flat substrates such as silicon wafers for semiconductor devices. The technique makes use of data contained in the cross-sectional profile of a laser beam which has been reflected from a sample under test. As described in the above patent, the basic technique relies on the sample under test being (a) perfectly flat and (b) aligned so that an incident probe beam is focused substantially normal to the surface of the sample. The applicants have therefore devised improvements to this technique which are described in detail in WO 2008/119982 Al, WO 2008/119984 Al, WO 2011/148143 A2 and WO 2011/148138 Al, each of which is incorporated herein by reference. These improvements variously provide generalisations to the basic BPS technique so that it can be applied to curved or misaligned films.

The applicants have now determined that the use of any or all of the BPS techniques described in the above applications and patents can be advantageously applied to measuring one or more properties of an ocular membrane in accordance with embodiments of the present invention.

Uniquely, such BPR techniques can be used to measure not only thickness but also refractive index and surface orientation. Furthermore, BPS is a safe, non-contact technique capable of making a large number of measurements in a short period of time.

The ocular membrane may, for example, be constituted by a cornea, a lens or a retina of an eye.

The property being measured may comprise one or more of thickness, refractive index, curvature, shape, surface orientation or alignment.

Accordingly, in particular embodiments, the measuring of the property of the ocular membrane may comprise Corneal Pachymetry (i.e. the measurement of the thickness of a cornea).

The property may be measured in vivo or in vitro. The property may be employed in any of the applications discussed in this specification.

The measurements obtained may be used to map the property, for example, to create an image showing variations in the property across the membrane.

In particular embodiments, BPR can be used to sample the ocular membrane properties to obtain a three dimensional map of the membrane. The sampling may be performed using a focused laser spot of, for example, approximately 1pm diameter, and wherein the laser is configured to scan across the membrane being measured.