JPH0452721Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention provides a tip for an immersion observation device that minimizes harmful reflected light when observing objects with low reflectivity using coaxial illumination and an immersion method. Regarding lenses.

Conventionally, when observing objects with low reflectivity, such as corneal endothelial cells in the human eye, the tip lens of the observation device is brought close to the cornea, and a corneal protector with approximately the same refractive index as the tear film on the corneal surface is used in between. It was filled with a medium to prevent reflections at the interface between the corneal protective medium and the cornea.

However, even with the liquid immersion method described above, reflection at the interface between the tip lens and the corneal protective medium cannot be prevented. This reflected light does not form an image on the imaging plane of the corneal endothelial cell image, but since the working distance of this type of optical device is short, around 1 mm, when the cornea is observed using the observation optical system, the corneal endothelial cell image is An image created by the reflected light appears near. Therefore,
When the width of the slit illumination light is increased, the corneal endothelium image and the reflected image of the slit illumination light by the interface between the tip lens and the corneal protective medium overlap, and the resolution contrast of the corneal endothelium image is significantly deteriorated.

Incidentally, various proposals have been made to prevent light reflected by the interface between the tip lens and the corneal protection medium from entering the observation optical system. The first proposed example is constructed by adhesively bonding a tip lens divided into two along the optical axis with an opaque layer interposed therebetween, and illuminating through one divided member and observing through the other divided member. Manufacturing this tip lens involves difficult operations such as cutting the lens and bonding through an opaque layer, and the adhesive used for bonding may have an adverse effect on the eyeball. The second proposed example consists of two members in which the distal lens is cut along a plane perpendicular to the optical axis, and the member on the eye side is arranged between the refractive index of the corneal protective medium and the refractive index of the other member. By selecting and configuring the material to have a refractive index, light reflected by the interface between the tip lens and the corneal protective medium is reduced. However, the refractive index value of transparent materials that can be used as tip lenses is limited, and the reality is that the reflected light is only slightly reduced compared to conventional lenses.

The purpose of the present invention is to provide an immersion type tip lens for an immersion type observation device that solves the above-mentioned conventional problems. A tip lens of an objective lens, which has a surface coating toward the tip lens consisting of a first layer of MgF ₂ and a second layer of SiO ₂ , and has a refractive index of 1.47 to 1.59. The reason is that the optical thickness of the first layer and the second layer is 1/4 of the design standard wavelength.

According to the present invention, reflection at the boundary between the immersion medium and the immersion tip lens can be prevented, and as a result, harmful reflected light can be effectively removed, and the peeling resistance is high and the initial performance can be maintained for a long time. It is possible to provide an immersion tip lens that can be maintained over a long period of time.

Hereinafter, a case in which the tip lens of the present invention is applied to an optical device for observing the corneal endothelium will be described in detail as a specific example.

On the back surface of the cornea of the human eye, there is a cell membrane called corneal endothelial cells, which is made up of tortoise shell-shaped cells approximately 20 microns in size. This corneal endothelial cell membrane is transparent like the corneal cortex and has a small contrast difference with the surrounding area, so it is difficult to observe with a general microscope, etc., so a special illumination observation method is used. That is,
A part of the illumination optical system and the observation optical system are shared, and a light splitting mirror is arranged in the observation optical system to introduce the illumination light flux.

The corneal endothelium observation optical device includes an observation optical system composed of a tip lens 3, a focusing lens 4, a relay lens 5, a light splitter 6, a photosensitive material 7, and an eyepiece 8, an illumination light source 9, a relay lens 10, Photography light source 11, condenser lens 12, slit 1
3 and an illumination optical system constituted by a mirror 14, and the mirror 14 introduces the illumination light flux of the illumination optical system into the observation optical system.

When observing corneal endothelial cells, the tip lens 3 is brought close to the cornea 1 of the eye to be examined, and the gap therebetween is filled with a corneal protective medium.

The observation light source 9 is placed at a position conjugate with the photography light source 11 with respect to the relay lens 10, and the light beam passes through the relay lens 10, the condenser lens 12, and the slit 13, and is reflected by the mirror 14, and then passes through the focusing lens. 4. Slit-shaped illumination is guided onto the cornea 1 through the tip lens 3 and the corneal protective medium 2.

The reflected light from the corneal endothelial cells caused by the illumination passes through the corneal protective medium 2, the tip lens 3, the focusing lens 4, the imaging lens 5, and the light splitter 6 to the eyepiece lens 8 or the photosensitive material 7. Each specimen is guided and recorded by visual observation or photography.

In addition, in this type of optical device, in order to prevent ghosts caused by reflections on the corneal surface, a tip lens made of a transparent material is placed at the tip of the illumination optical system and observation optical system, and this tip lens is attached to the corneal surface. The object is brought into contact with the object directly or through a liquid, and illumination observation is performed through this tip lens.

Physiological saline or a corneal protective medium is used as this type of liquid, and its refractive index is the refractive index of the cornea.
It is 1.33 which is almost equal to 1.376. Therefore, it is said that almost no reflection occurs at the interface between the corneal protective medium and the cornea.

However, even if the refractive index of the tip lens is 1.5, the refractive index gap between the corneal protective medium and the tip lens is 0.35%, which is too large compared to the reflectance of about 0.02% in the corneal endothelial cells. As mentioned above, even if the image is not formed, it becomes an obstacle to observation.

Conventionally, various antireflection films have been applied to the surfaces of optical members such as lenses in order to prevent reflection at boundary surfaces. However, these were done to prevent reflection from the air.
Even if this is applied to an immersion-type tip lens, it does not sufficiently achieve the desired anti-reflection function, and its reflectance is also quite high.

First, when the antireflection film is formed as a single layer, the refractive index n of the film is expressed as n ² =n _p n _g where n p is the refractive index of the corneal protective medium and n _g is _the refractive index of glass.

In the case of this single layer, the reflectance in the central wavelength region is generally low, but the reflection in the peripheral region tends to increase _rapidly . 2, B. I can't think of anything other than the structure shown in FIG. 2, A, in which the tip lens is made of fluorite and MgF ₂ is vapor-deposited thereon, but this is impractical. In other words, fluorite is expensive, and evaporating a _MgF2 film on the surface of fluorite is quite difficult, and the resulting film has poor adhesion and is easily peeled off. This is a problem because it can cause scratches.

Next, when antireflection is performed using a multilayer film, the following three-layer structure can be considered by analogy with conventional antireflection films. That is, a third layer: a film having a refractive index n ₃ slightly higher than that of glass is deposited to an optical thickness of λ/4 toward the substrate. (Tawashi,
λ represents the design reference wavelength. same as below. ) Second layer: deposit a film of refractive index n ₂ with optical thickness λ/2.

First layer: A film with a refractive index n ₁ is deposited to an optical thickness of λ/4.

The anti-reflection condition at the center wavelength of this film is n _g n ² ₁ n _p n ² ₃ (where n _g and n _p are as defined above).

Furthermore, in order to achieve low reflectance over the entire visible range, the second layer with an appropriate refractive index is coated with an optical thickness of λ/
In theory, anti-reflection can be achieved by vapor-depositing with 2.

However, in cases where anti-reflection of 0.02% or less is required, adopting a three-layer structure is highly dangerous. This is because the reflectance is increased once in the third layer, and errors in film thickness and refractive index sensitively affect the reflectance, making it extremely difficult to manufacture a desired film.

Furthermore, there is a concern that the refractive index of materials with high refractive index is generally unstable, so a three-layer structure cannot be adopted.

For the above reasons, the present invention has decided to adopt an antireflection film having the following layer structure.

In this invention, in order to reduce the refractive index gap in a certain direction and as much as possible, we select a material with the lowest possible refractive index as the tip lens material.
M _g F ₂ (λ/4) and SiO ₂ (λ/4) toward the substrate to approximate the refractive index of the corneal protective medium, 1.33.
We decided to adopt the following membrane configuration. Its schematic configuration is shown in FIG.

In Figure 3, the design standard wavelength is 520nm, and the first layer
The reflectance characteristic curves when MgF ₂ and the second layer of Si0 ₂ are deposited with an optical film thickness of 520 nm/4 (hereinafter simply referred to as film thickness) on tip lenses with refractive indexes of 1.48, 1.50, and 1.57 are shown in A, B, and A, respectively. It is shown by C.

As is clear from the reflectance characteristic curve in Figure 3, it can be seen that the reflectance characteristic shown by curve B, where the refractive index of the tip lens is 1.50, is optimal as the reflectance is kept low over the entire visible range. .

However, even if the refractive index of the tip lens is slightly changed to 1.48 or 1.53, curves A or C
It is also clear that the product is durable enough for use.

In Figure 4, the refractive index of the tip lens is 1.51, the components of the first layer and the second layer are the same as in Figure 3, and the film thickness is 480 nm/4 for the first layer and 560 nm/4 for the second layer.
Curve A shows the reflectance transmission characteristic curve when the wavelength is 4, and curve B shows the characteristic curve when the first layer is 560 nm/4 and the second layer is 480 nm/4.
C shows the characteristic curve when the thickness is 520 nm/4 and the second layer is 440 nm/4.

As is clear from the three characteristic curves in FIG. 4, it can be seen that the film thicknesses of the first layer and the second layer are not subject to severe restrictions and have a wide allowable range.

In Figure 5, the design standard wavelength is 520 nm, the first layer is made of MgF ₂ , the second layer is made of glass for vapor deposition,
At a film thickness of 520nm/4, the refractive index is 1.53, 1.55, and
The reflectance characteristic curves when deposited on a 1.57 tip lens are shown as A, B, and C, respectively.

The results in FIG. 5 also show the same tendency as FIGS. 3 and 4.

As is clear from the above description, if immersion observation is performed using the immersion tip lens coated with the above-mentioned anti-reflection film, even if the reflectance of the object to be observed is low and the contrast difference with the surrounding area is quite low, Observation is not obstructed by reflected light from the boundary between the tip lens and the immersion liquid.

[Brief explanation of drawings]

FIG. 1 is an optical layout diagram of an optical device for observing the corneal endothelium, FIG. 2 is a diagram showing the reflectance characteristics of a tip lens having a single antireflection film, and FIGS.
6 is a diagram showing the reflectance characteristics of the tip lens of the present invention each having an antireflection film consisting of two layers, and FIG.
1 is a schematic diagram of a tip lens coated with an antireflection film according to the present invention. a...first layer, b...second layer, c...tip lens.

Claims (1)

[Scope of utility model registration request] This is the tip lens of an objective lens that is used by immersing it in an immersion medium _.
The tip lens has a surface coating consisting of a first layer of SiO ₂ and a second layer of SiO 2 , and the refractive index of the tip lens is 1.47 to 1.59, and the optical thickness of the first layer and second layer is equal to the design reference wavelength. A tip lens for liquid immersion, characterized by its 1/4 size.