In the precision field of ophthalmic diagnosis, when ordinary slit lamp microscopes cannot touch the secrets deep in the fundus, a key optical "bridge" - double aspheric lenses show irreplaceable value. It does not operate independently, but cooperates with the slit lamp microscope to expand the field of view to every subtle corner of the retina, which constitutes one of the important criteria for the diagnosis of diseases in the posterior segment of the eye in modern times.
The optical design of the slit lamp itself is mainly used to visualize the anterior segments (e.g., cornea, anterior chamber, lens). Its working distance is limited, and light scatters after passing through the pupil, making it difficult to form clear, magnified, high-resolution images on the retina. The core role of the double aspheric lens is to overcome this physical limitation. The ophthalmologist can project a slit lamp into the pupil area, gather on the cornea, and then place the double aspheric lens about 10mm in front of the subject's eyes, with the convex side of the anterior mirror facing the examiner. With the backward movement of the slit lamp, the slit lamp, the lens and the pupil of the examined eye achieve three points and one line, and finally a clear and three-dimensional fundus image can be seen.
The 20D, 78D and 9D are designed with special biconvex lenses to create a certain space between the lens and the cornea. Because there is no need to touch the cornea, patient comfort is higher, the risk of infection is minimal, and a wide field of view image is obtained. In recent years, double aspheric lens has been increasingly widely used in pediatric examinations, rapid screening and surgery.
Product Features:
20D Aspheric Lens:
o Field of view：46°
o Magnification Ratio: 3.13X
o Working Distance: 50mm
o Clear Aperture: 48mm
o Dimension: 56*20mm
o It is suitable for scenarios that require extensive fundus viewing, but the ability to display details is weak
78D Aspheric Lens:
o Field of view：81.4°~ 97°
o Magnification Ratio: 0.93X
o Working Distance: 8mm
o Clear Aperture: 26mm
o Dimension: 33*15mm
o It achieves a good balance between field of view and magnification, with a moderate field of view and a magnification effect better than 90D lenses. It is one of the most frequently used models in clinical practice, especially for the posterior pole retina.
90D Aspheric Lens:
o Field of view：74.2°~ 89°
o Magnification Ratio: 0.76X
o Working Distance: 7mm
o Clear Aperture: 21mm
o Dimension: 27*13mm
o The depth of field is large, the field of view is wide, and the three-dimensional sense is strong, but the fundus image is an inverted virtual image. It is close and helps to see through the small pupil, but may cause mirror fogging due to proximity to the cornea
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