WO1990001291A1

WO1990001291A1 - Infrared videorefractometer particularly for application in pediatric ophthalmology

Info

Publication number: WO1990001291A1
Application number: PCT/EP1989/000882
Authority: WO
Inventors: Mario Angi
Original assignee: Mario Angi
Priority date: 1988-08-05
Filing date: 1989-07-27
Publication date: 1990-02-22
Also published as: AU3977989A; IT8841650A0; IT1226526B

Abstract

An infrared videorefractometer particularly for application in pediatric ophthalmology, caracterised by comprising: at least one infrared radiation source (2), a closed-circuit television apparatus complete with a telecamera (1) sensitive to said infrared radiation, and a monitor (3) on which the image taken by said telecamera (1) can be displayed, and a computer (6) for analyzing, handling and processing the data obtained from the acquired image and/or from suitably prearranged files.

Description

Infrared videorefractometer particularly for

application in pediatric ophthalmology

This invention relates to an infrared videorefractometer particularly for pediatric ophthalmology applications.

In the ophthalmological field a well known technique is that of static refraction, which enables the refractive stats of the eyes and the possible presence of strabismus to be evaluated by analyzing the corneal and retinal reflections generated by a light source positioned slightly eccentric to the observer's eye.

When the refractive defect in the eye under examination exceeds a critical value characteristic of the apparatus used, a luminous crescent appears on the pupillary area.

The application of said technique to the pediatric field involves however considerable difficulties due to the fact that the currently used instruments employ light radiation in the visible spectrum, such radiation being poorly tolerated because it generates glare.

A further drawback derives from the fact that for proper eye exploration the pupil must be dilated with mydriatic collyria, which can involve the risk of serious toxic reaction.

A long time is also required for the medicament to exhaust its effect, which, includes disturbance to the vision luring pupil dilation.

A further drawback is due to the fact that as the child's face is often moving it is difficult to properly frame its eyes.

To prevent glare affecting the child and obtain non- pharmacological mydriasis it is known to use infrared-sensitive instruments known as 10 autorefractometers, employed in a lowluminosity environment. Said instruments are however unsuitable for diagnostic use in early childhood as they require the immobility of the subject during the examination, which is conducted at close distante (8-10 cm).

An object of the present invention is to obviate all the aforesaid difficulties by providing an instrument applicable in the pediatric ophthalmological field which is used at an operating distance such as not to alarm the child. A further object is to allow continuous inspection of the child's eye in order to be able to observe its accomandative behaviour, and to fix the pupil images in the optimun position for subsequent diagnostic analysis.

A further object is to provide an instrument which uses light radiation outside the visible spectrum. A further object is to provide an instrument which can be used without requiring pupil dilation by pharmacological mydriasis.

A further object is to provide an instrument which is able to unequivocally attract the attention of the subject under examination towards the imagetaking lens.

All these and further objects which will be apparent from the description given hereinafter are attained according to the invention by an infrared videorefractometer particularly for applications in pediatric ophthalmology, characterised by comprising:

- at least one infrared radiation source,

- a closed-circuit television apparatus complete with a telecamera sensitive to said infrared radiation and a monitor on which the image taken by said telecamera can be displayed, and - a computer for analyzing, handling and processing the data obtained from the acquired image and/or from suitably prearranged files.

A preferred embodiment of the present invention is described in detail hereinafter with reference to the accompanying drawings in which: Figure 1 is a perspective view of an infrared videorefractometer:

Figure 2 is a detailed view of the telecamera lens; and

Figure 3 shows the block diagram of the videorefractometer according to the invention.

As can be seen from the figures the videorefractometer according to the invention consists of a closed-circuit television apparatus complete with a telecamera 1 sensitive to infrared emissions from a source 2, and a high resolution monitor 3.

In the region of the lens 4 of the telecamera 1 there is provided a system of coloured leds 5 arranged to attract the attention of the subject under examination.

The light source 2 necessary for generating the corneal and retinal reflections consists of three off-centered infrared lamps disposed about the lens at 0, 90 and 130 to each other.

The closed-circuit television apparatus is connected to a normal processing system for acquiring, recording and handling the images received from the telecamera 1. Said system comprises a computer 6 equipped with a hard and floppy disks and connected to the monitor 3, an alphanumerical keyboard 7 and a printer 8.

The system is provided with software specifically written for handling the images received from the telecamera 1 and for processing all the data required for the diagnosis, as obtained from said images and from suitably created files.

With the exception of the keyboard 7 and printer 8, thε hardware is housed in a vertically extending container 9 which enables the operator to follow the subject under examination without being seen, and thus without distracting his attention.

To make a complete analysis of the eye of the 15 patient he is first made to sit behind the refractometer so that his eyes face the source 2 and the telecamera 1. The operator faces the other side of the videorefractometer, ie the side comprising the monitor 3 and keyboard 7.

To make the analysis, the operator firstly darkens the environment to a light level such as to cause dilation of the patient's pupil, and then turns on the coloured fixation leds plus one of the three infrared sources 2. The infrared radiation illuminates the pupil and on the basis of the known static refraction technique enables the refractive state of the eye and the presence of any strabismus to be evaluated by observing on the monitor 3 the corneal and retinal reflections generated by the light source 2 5 positioned eccentric to the image-taking lens 4 of the telecamera 1.

In practice, by means of the monitor 3 which provides real-time analog display of the inspection effected by the telecamera 1, the operator is able to aim at the subject under the best image-taking conditions (field, focal distance, fixing position on the telecamera lens).

when these optimum conditions have been attained the operator fixes the image on the monitor and transfers the relative data into the computer memory so that they can be processed to determine the possibile presence of a luminous crescent in the pupil area. In particular, the width of this crescent is defined by the known equation:

where: R is he pupil radius of the examined subject

E is the distance of the light source 2 from the edge of the aperture of the lens 4

Y is the parallax between the eye and the edge of the aperture of the lens 4

d is the distance of the subject from the telecamera 1

D is the extent of the refractive defect.

The position of the crescent in the pupil area is determined by the radial position of the light source about the lens 4 and the sign of the refractive defect D, this being contralateral to the source in the case of hypermetropia and ipsilateral in the case of myopia.

If the values R, E, Y and d are kept constant in the equation, the width of the luminous pupil crescent will depend only on D, so allowing semiquantitative evaluation within the limits of thε apparatus sensitivity.

For a complete analysys of the examined eye the operation is repeated using the other infrared sources 2 in succession, allowing images to be obtained along illumination meridians variable from 0 to 180.

By means of the software executed in the computer the operator is able to process and obtain all the data required for forming an exact diagnosis.

Said data are obtained from the image displayed on the monitor 2 and/or taken from suitably prearranged files.

From the aforegoing it is apparent that the infrared videorefractomwter according to the invent ion;

- overcomes the need for subject immobility during the examination;

- enables an operating distance from the lens 4 of the telecamera 1 to be used which is such as not to alarm the child;

- allows non-pharmacological mydriasis to be used; - prevents glare which would be intolerable to the child

- allows the optimum image-taking conditions to be fixed;

- allows rapid acquisition, processing, digitalizing and recording of the data received from the telecamera or from suitable files.

Claims

1. An infrared videorefractometer particularly for application in pediatric ophthalmology, characterised by comprising:

- at least one infrared radiation source (2),

- a closed-circuit television apparatus complete with a telecamera (1) sensitive to said infrared radiation, and a monitor (3) on which the image taken by said telecamera (1) can be displayed, and

- a computer (6) for analyzing, handling and processing the data obtained from the acquired image and/or from suitably prearranged files.

2. A videorefractometer as claimed in claim 1, characterised by comprising a plurality of infrared radiation sources (2) disposed within a band concentric to the lens (4) of the telecamera (1).

3. A videorefractometer as claimed in claim 2, character i sed in that the infrared radiation sources (2) are disposed at 0, 90 and 180 to each other.

4. A videorefractometer as claimed in claim 1, characterised by comprising means (5) for attracting the attention of the child.

5. A videorefractometer as claimed in claim 4, characterised in that the attracting means (5) consist of light emitting diodes.

6. A videorefractometer as claimed in claim 5, characterised in that the light emitting diodes (5) are disposed in proximity to the centre (4) of the telecamera (1) is lens (4).

7. A videorefractometer as claimed in claim 1, characterised in that the monitor (3), telecamera (1), computer (6), infrared radiation sources (2) and attracting means (5) are housed in a vertically extending container (9).

8. A videorefractometer as claimed in claim 7, charactherised in that the telecamera (1), the infrared radiation sources (2) and the attracting means (5) are housed on the opposite side to the

(3).