Orbscan topography (synonym: Orbscan I) is a modern procedure in ophthalmology that allows pachymetry (measurement of corneal thickness) and analysis of the anterior chamber structures of the eye (lens, iris). Corneal thickness is a parameter of tremendous importance and is used to determine corneal function.
Indications (areas of application)
- Checking the function of the corneal endothelium (cell layer of the cornea that has the functions of maintaining the water supply and the transparency of the cornea), which allows conclusions about the change of the cornea when wearing contact lenses.
- Postoperative assessment of a keratoplasty (corneal surgery in which either by means of a transplant – organ donation of the cornea – or by the action of physical force on the cornea is aimed at a change in refractive power), the corneal thickness is attributed prognostic significance (outlook on the success of the treatment).
- Evidence of a metabolic disorder (metabolic disorder) with impairment of corneal function.
- Present glaucoma (glaucoma – increase in intraocular pressure), as reduced corneal thickness in the center is associated with worse progression of glaucoma.
The procedure
The Orbscan I system is based on the use of a slit lamp, which is also commonly used outside of pachymetry in practical ophthalmology. The slit lamp provides the ophthalmologist with the ability to direct a beam of light that is variable in width and dispersion onto the patient’s eye, allowing inspection of the various areas of the eye, including the retinal sections (retinal segments). Slit lamp-assisted pachymetry with integration of the computerized Orbscan I system allows non-contact (performed without touching) measurement of the thickness of the cornea (cornea). The Orbscan I allows accurate analysis of the front of the corneal surface through a color and image display that provides the treating physician with an assessment of the radii of curvature of the corneal surface. The following features of the examination using the Orbscan I topographer should be emphasized:
- The person being examined rests his or her head in a slit-lamp-like device and fixes a point at a defined distance.
- Following this, light rays are used to create a reflection (mirroring), where the returning directional rays are evaluated by the cornea via a computer-controlled video card.
Orbscan II, which resulted from the further development of the Orbscan I system and allows assessment of both the anterior and posterior sides of the entire corneal surface, offers the option of assessing the entire anterior segment of the eye by scanning through a slit of light, in addition to examining corneal thickness. The procedure for using the Orbscan II system is as follows:
- By measuring with a Placido system (projection of circles onto the cornea to assess the surface), a surface analysis of the cornea can be performed.
- For measurement, 40 slit images are taken at an angle of 45 degrees to the surface of the eye.
- Then, using the measurement technique of triangulation (optical distance measurement method) and ray tracing method (light ray tracing), it becomes possible to calculate both the corneal thickness and other parameters.
Orbscan topography is particularly in the advanced form (Orbscan II) in the imaging diagnostics of ophthalmology of great importance, because a detailed analysis on the one hand the anterior and on the other hand the posterior surface of the cornea, a measurement of corneal thickness and the depth of the anterior chamber of the eye can be achieved. The outstanding advantage of the procedure is the non-contact examination, which takes only a few minutes and can reveal contraindications (contraindications) such as insufficient corneal thickness for, for example, a laser intervention. Furthermore, it is hoped that the determination of corneal volume using the Orbscan II method will also improve the assessment of the quality of cataract operations (surgical procedures to remove a cataract – clouding of the lens).
