Patent Description:
The measurement of intraocular pressure (IOP: IntraOcular Pressure) represents a fundamental moment of the routine ophthalmological examination, as the increase of its value represents a major risk factor for glaucoma and is one of the fundamental parameters for the diagnosis of this disease, together with the evaluation of the optic disc and the examination of the visual field.

Tonometry is a procedure that allows an indirect measurement of IOP, based on the relationship between intraocular pressure and the force necessary to modify the natural shape of the cornea, using instruments called tonometers.

In the following, reference will only be made to the "applanation" tonometers, to which the invention disclosed herein applies. They measure the force required to flatten a surface having a known area of the cornea or evaluate the width of the area flattened by a predetermined fixed force. In particular, Goldmann's applanation tonometer, now universally used, represents the international standard for measuring IOP.

The Goldmann tonometer, depicted in <FIG>, includes a flattening element, or head, reusable or disposable, consisting of a typically transparent plastic head intended to come into contact with the patient's eye. The head of the tonometer, containing one or more prisms, is joined by means of a rod to a spiral spring. By means of a lateral graduated knob it is possible to vary the value of the force applied to the cornea by means of the head of the tonometer. <CIT> discloses such a tonometer.

The examination technique involves placing the instrument on a special base of a slit lamp, shown in <FIG>. After corneal anesthesia, the folded end of a strip of filter paper soaked in ophthalmic dye, a fluorescent substance that serves to make the edge of the smoothed area more evident by observation with blue light, is applied to the patient's lower conjunctival fornix. A widely used ophthalmic dye is fluorescein, which emits an intense yellow-green fluorescence in the <NUM>-<NUM> wavelength range when excited by blue light radiation in the <NUM>-<NUM> range (or by ultraviolet radiation in the range <NUM>-<NUM>). As an alternative to fluorescein, riboflavin is used, which emits yellow-green fluorescence in the <NUM>-<NUM> range when excited by blue light radiation in the <NUM>-<NUM> range (or ultraviolet radiation in the <NUM>-<NUM> range). Identifying the edges of the flattened area with good precision is essential for a correct measurement of ocular pressure.

The patient is seated in front of the slit lamp and asked to observe a reference point, as shown in <FIG>. The slit of the lamp is opened to the maximum and a cobalt blue filter is placed in front of it to better visualize the ophthalmic dye, that is, to better visualize the edges of the smoothed area. A light beam is then directed so that it passes through the transparent prism and the knob is adjusted to the notch corresponding to <NUM> mmHg. The slit lamp is moved forward so that the prism gently contacts the central part of the cornea, as in <FIG>.

The prism, contained in the transparent plastic head, splits the circular image of the flattened corneal surface into two semi-annuli, one on top of the other. Then through the eyepiece, you can see two green semi-annuli in a blue luminous field.

<FIG> shows what is observed with the Goldmann tonometer in different cases. The side knob of the tonometer is rotated in such a way as to bring the two semi-annuli into contact with their inner edge. Depending on the pressure exerted, different configurations of the semi-annuli can be observed: if they are far away it is necessary to increase the applanation force, if they overlap it is necessary to rotate the knob in reverse to decrease the exerted force. In <FIG>, the semi-annuli appear relatively thick due to excessive use of ophthalmic dye; in <FIG> the semi-annuli have an adequate thickness but are not correctly aligned because the applanation force is excessive; in <FIG>, the applanation force is insufficient; in <FIG> the semi-annuli are correctly aligned.

The ability to correctly identify the two semi-annuli, their respective ends and their respective internal edges is a crucial factor for the correct calibration of the instrument and it is not easy for the physician to completely discriminate the two green semi-annuli within the predominant blue luminous field.

A solution to facilitate the visualization of the semi-annuli involves the insertion of a yellow filter-barrier above the eyepiece of the slit lamp. It filters out blue light to make the fluorescent green stand out more clearly. Filters available on the market are characterized by transparent yellow lenses, with a reduced thickness, about <NUM>. However, the use of a filter with a reduced thickness, in addition to requiring the purchase of an additional component (the filter itself), constitutes the only element for filtering the intense light radiation coming from the patient's eye, sometimes making it difficult, for the physician, the distinction of the thin green semi-annuli immersed in a field of blue light and therefore does not constitute an optimal solution.

It would be desirable to improve the filtering of blue light from the patient's eye during a tonometry measurement and eliminate the need to purchase an additional component such as a yellow barrier filter for the slit lamp used during this measurement test.

The subject of this disclosure is an applanation head for a Goldmann applanation tonometer, as well as a related Goldmann applanation tonometer, with integrated yellow filter-barrier coloring.

The addressed problem is solved by means of a Goldmann applanation tonometer head according to claim <NUM>.

Preferred features of the invention are the subject of the dependent claims.

A disposable kit for intraocular pressure measurement with a Goldmann applanation tonometer is also disclosed, comprising a package containing a Goldmann applanation tonometer head according to this disclosure, and a single-dose bottle filled with a liquid dye for ophthalmic use or a paper strip soaked with a liquid or powder dye for ophthalmic use.

Other advantages and characteristics of the present invention will become evident from the following detailed description of some embodiments, presented by way of nonlimiting example with reference to the attached drawings, in which:.

An exemplary embodiment of an applanation head <NUM> for a Goldmann tonometer <NUM> according to this disclosure is schematically illustrated in <FIG>. In the following reference will be made to this embodiment, which is preferred, although several other embodiments are possible.

The head <NUM> for Goldmann applanation tonometer <NUM> according to this disclosure is made of a transparent polymeric material, for example in Polymethylmethacrylate (PMMA) and defines:.

Studies carried out by the applicant have shown that, by making the head for tonometer in a transparent yellow material, with a carefully determined hue and saturation, it is possible to avoid the use of the common yellow barrier filters, guaranteeing an effective filtering of the blue light radiation through the optical path of the tonometer head, making the semi-annuli more visible during the measurement of intraocular pressure with applanation tonometry.

Unlike the common applanation heads for Goldmann tonometers, the applanation head <NUM> according to this disclosure has at least one portion <NUM> characterized by a transparent yellow color. Said at least one portion <NUM> comprises the applanation surface <NUM> and defines optical prisms <NUM> configured to visualize as two circular semi-annuli a substantially circular perimeter of a cornea flattened against the flat corneal applanation surface <NUM>. According to this disclosure, the coloring of this transparent portion is of a different intensity of yellow than common barrier filters, as will be described below.

The transparent yellow color is obtained by adding a dye during the polymerization phase of said transparent polymer in correspondence with said at least one portion <NUM>, in a quantity ranging from <NUM> to <NUM>% (w / w). According to a preferred embodiment of the present invention, the dye used is of the type currently known under the trade name RENOL™ yellow produced by Clariant, added at <NUM>% (w / w) in the polymerization phase of PMMA. Preferably, this yellow dye is selected from the set consisting of yellow dyes suitable for PMMA coloring. According to one aspect, a suitable yellow dye may be of the type provided in concentrated form in a masterbatch using a carrier composed of PMMA (polymethyl methacrylate) or SAN (styrene acrylonitrile).

An applanation head <NUM> according to the present disclosure is characterized by a macroscopically lighter yellow color than the common commercially available tonometry filters. In fact, with a reduced thickness, generally <NUM>, the filtering action of common filters is mainly due to the filtering power of an intense yellow hue.

Making an applanation head <NUM> with the same coloration as common barrier filters would not be optimal for the tonometer measurement, since the blue excitation light, coming from the slit lamp <NUM> and directed to the patient's cornea, passes always through a terminal portion of the applanation head of the tonometer, in a diagonal direction with respect to said Y axis, as shown in <FIG>. The attenuation of the impinging blue light could limit the excitation, or not excite at all, of the ophthalmic dye on the cornea and make measurement impracticable.

Consequently, it is desirable that the coloring of said portion <NUM> of the applanation head <NUM> according to this disclosure be relatively light.

This shade, following the experimental confirmation made by the Applicant, allows an optimal passage of the blue radiation of excitation of the ophthalmic dye so that the latter is excited and emits fluorescence in the yellow spectrum in an optimal manner for the success of the measurement.

A filter with a thickness similar to that of common barrier filters, about <NUM>, and with the attenuated yellow color described above would not be efficient in filtering the blue light reflected from the cornea and directed to the eyepiece <NUM> of the slit lamp <NUM>, for obvious reasons. However, the blue light intended to excite the ophthalmic dye only passes through a limited terminal portion of the applanation head <NUM>, with a diagonal incidence with respect to the Y axis. The reflected blue light, on the other hand, travels the entire optical path of the applanation head <NUM>, in direction parallel to the Y axis, crossing a larger volume of the same. As a result, the blue light reflected from the cornea is attenuated more than the blue light directed from the slit lamp towards the cornea. The Applicant noted that, thanks to an appropriate calibration of the yellow color of the transparent body <NUM>, the semi-annuli stand out more against the blue background of the light reflected by the cornea, allowing a more accurate detection of the patient's intraocular pressure.

The criteria used by the Applicant for the characterization of the yellow color are indicated below.

To characterize the yellow color of the transparent mixture that constitutes the transparent body <NUM> of the tonometer head, reference was made to the ASTM E313 standard in force in <NUM>.

According to this standard, the classification of the yellow color is based on the L * a * b colorimetric model defined by the International Commission for Illumination (CIE), also known as CIELab, in which a color is indicated by three values:.

The CIELab model is widely used in industrial practice as it covers the entire spectrum visible to the human eye, representing it uniformly and constitutes an independent model regardless of any graphic technology that may be used by different users. The CIELab values may indeed be easily matched to the simplest representation indexes of the chromatic scales such as RGB and CMYK values, a methodology used by well-known graphic imaging and manipulation software.

According to the ASTM E313 standard in force in <NUM>, for the characterization of the specific yellow color, a Yellowness Index (YI - Yellowness Index) may be calculated as follows: <MAT> where X, Y, Z are the values known as CIE tristimulus values, and the coefficients depend on the illuminant and on the observer, as indicated below.

Further details on the measurement method are indicated in the official ASTM publications concerning the ASTM E313 standard, incorporated herein by reference.

A measurement of the CIELab parameters and the Yellowness Index (YI) was carried out on homogeneous parallelepiped-shaped sample plates, made using the mixture object of the present invention, having the following dimensions: <MAT> <MAT> <MAT>.

The device used for measuring the CIELab parameters is a spectrophotometer of the type currently known under the trade name CM 3600A from Konica Minolta, but other devices for measuring CIELab parameters may be used to obtain corresponding measurements.

The light radiation used for the measurements is classified as CIE Standard Illuminant D65, according to ISO <NUM>-<NUM>: <NUM> (E) / CIE <NUM>-<NUM> / E: <NUM>, in force in <NUM> using a CIE <NUM> standard colorimetric observer placed at an inclination of <NUM>° from a vertical axis perpendicular to the planar development of the plate.

In this condition of measurement, the YI Yellowness Index of a mixture suitable for making a disposable applanation head according to this disclosure was found to be between: <MAT>.

The CIELab parameters relating to the shade of yellow were found to be included between the following values: <MAT> <MAT> <MAT>.

The tables shown in <FIG> report the values of the CIELab and YI parameters measured on sample plates made using suitable transparent yellow mixtures according to the present disclosure.

According to one aspect, the yellow coloring of the portion <NUM> of the transparent body <NUM> is identified by means of the CIELab model by means of said parameters L, a, b, where:.

<FIG> shows the transparency spectrum T (%) of the applanation head <NUM>, made according to a preferred embodiment of the present disclosure, wherein the transparency spectrum is expressed as a percentage and indicates the amount of radiation shielded by the sample, wherein a value T = <NUM>% indicates complete shielding and a value T = <NUM>% indicates complete transparency at the specific wavelength. The diagram shows how the blue radiation, whose spectrum includes wavelengths between <NUM> and <NUM>, reflected by the cornea and covering the entire portion <NUM> of the applanation head is suitably filtered, and the transparency at longer wavelengths as the green light, <NUM>-<NUM>, is almost maximum.

The solution object of the present disclosure is particularly convenient for making disposable applanation heads for Goldmann tonometers. In practice, with the applanation head <NUM> for a Goldmann tonometer <NUM> according to this disclosure, it is possible to measure the IOP in the usual way, since the applanation head <NUM> according to this disclosure can be mounted on the rod of any Goldmann tonometer of a known type, allowing, however, to visualize much better the yellow-green semi-annuli on the blue background.

Conveniently, the applanation head of the present disclosure may be distributed in kit for intraocular pressure measurement with a Goldmann applanation tonometer, which will comprise a sterile package containing an applanation head according to the present disclosure, together with a bottle filled with a liquid dye for ophthalmic use or a strip of paper soaked with a liquid or powder dye for ophthalmic use.

According to one aspect, the bottle will be of the single-dose type and will contain an adequate amount of liquid dye for ophthalmic use, such as fluorescein or riboflavin, to be applied entirely on the corneal surface before carrying out the measurement. Such a kit will provide the doctor with all the consumables necessary to perform a single intraocular pressure measurement and its opening in the presence of each patient will give the patient the certainty that the applanation head used is definitely sterile.

Given that normally two drops of ophthalmic dye are used for each measurement and that the risk of contamination of the ophthalmic dye is extremely low, the kit will conveniently contain multiple individually packaged applanation heads according to this disclosure and a multidose reclosable bottle of ophthalmic dye, which can be a liquid dye, for example based on fluorescein or riboflavin, containing an amount of dye sufficient to perform a number of intraocular pressure measurements corresponding to the number of applanation heads contained in the kit.

Claim 1:
A disposable applanation head (<NUM>) for a Goldmann applanation tonometer (<NUM>), comprising:
a transparent body (<NUM>) to at least one type of visible light, having a flat corneal applanation surface (<NUM>), configured to be pressed against a cornea of an eye so as to flatten it, wherein at least a portion (<NUM>) of said transparent body (<NUM>) defines optical prisms (<NUM>) configured to visualize as two circular semi-annuli a substantially circular perimeter of a cornea flattened against the flat corneal applanation surface (<NUM>);
characterized in that said transparent body (<NUM>) is made of a solidified mixture of transparent polymer with a yellow dye, in which a type and a percentage of said yellow dye of said mixture are determined so that a sample plate, shaped like a parallelepiped, of said solidified mixture having the following dimensions: <MAT> <MAT> <MAT>
when this sample plate is illuminated by means of a CIE Illuminant Standard D65 radiation as referred in the ASTM E313-<NUM> standard published on January <NUM>st, <NUM>, the measurement sensor being a CIE <NUM> Standard Colorimetric Observer, as referred in the ASTM E313-<NUM> standard published on January <NUM>st, <NUM>, positioned at <NUM>° from a vertical axis perpendicular to a planar development of the plate, has a yellow color identified by a CIELab colorimetric model, as referred in the ASTM E313-<NUM> standard published on January <NUM>st, <NUM>, as a function of parameters L, a, b, wherein:
L between <NUM>% and <NUM>%
a between -<NUM> and -<NUM>
b between <NUM> and <NUM>.