**2. History**

The earliest attempts at elective pars plana vitreous surgery were directed toward cutting opaque vitreous. While still not used for the diagnosis of the etiology, papers as early as the 19th century report on the procedure in the context of ocular inflammation. Bull reported in 1890 on 17 cases in which a pars plana approach (first introduced by Von Graefe in 1863) involving a discission needle introduced through the pars plana was used to cut vitreous membranes resulting from inflammation or hemorrhage. [1]

The 1970s were a period of major advancement in the field of pars plana vitrectomy (PPV), with the introduction of advanced instrumentation, such as the vitreous-infusion-suctioncutter (VISC). Indications for diagnostic procedures and the diagnostic methods themselves were limited at that time. In a review paper from 1974, Michels et al. [1] described vitreous biopsy as a procedure that is rarely needed, with the most frequent indications being mycotic endophthalmitis and reticulum cell sarcoma. The diagnostic methods that were mentioned included only cytology and culture. Vitrectomy for endophthalmitis was also mentioned in this paper, and showed that performing the procedure for this entity was a novelty.

One of the first papers to describe diagnostic vitrectomy was published by Engel et al in 1981. [2] Findings resulting from early procedures in that era included ocular tumors such as reticulum cell sarcoma and leukemic infiltration, as well as infectious entities such as fungal endophthalmitis and acute retinal necrosis (ARN). The methods described there included cytology, histopathology, and ultrastructural studies, with "new" methods such as using a millipore filter and celloidin-bag cell-block techniques.

Since these early days, the field of diagnostic procedures has advanced rapidly. Methods including polymerase chain reaction (PCR), flow cytometry, and other advanced methods introduced in the general field of medicine have been adopted by ophthalmologists for use in ocular diagnostic procedures. With the introduction of these methods, the list of etiologies that can be recognized by invasive diagnostic techniques has also expanded, as will be described here.
