UFO (Unidentified Full Objects) Sighted in The Cornea: Can We Make The Diagnosis By Means of in vivo Confocal Microscopy?
Introduction
In vivo confocal microscopy (IVCM) is a
powerful diagnostic technique that provides minimally invasive, high
resolution, steady-state assessment of the corneal cellular structure [1]. Rapid scanning is used to recreate a full field of view and to get a “real time” viewing [2]
Because of its ability to analyze living tissue at cellular levels,
IVCM represents a valid tool for clinical diagnosis and management of
corneal diseases [3].
It may be useful in the areas of infective keratitis, corneal
dystrophies, refractive surgery, and contact lens wear, where it allows
for differential diagnosis and detection of subtle short and longterm
changes [2]. In our study, we evaluate the efficacy of IVCM in the diagnosis of corneal disease.
Materials and Methods
Thirty eyes of 30 patients with corneal diseases were
included in the study. All patients underwent IVCM and color picture of
the anterior segment. A color photograph of the entire ocular surface
of each eye was obtained using a slit lamp and Ekta chrome, 16x
magnification.
Heidelberg Retinal Tomograph with Rostock Corneal
Module (HRT-RCM) (Heidelberg Engineering, GmBH, Dossenheim, Germany) was
used to evaluate the corneal structure. The system design and use of
this confocal microscope have been described in detail [4].
Before the examination, a drop of a topicalanesthetic, proparacaine
hydro chloride ophthalmic solutionof 0.5%, was administered to the
cornea, and a drop of 2.5% hydroxyl propyl methyl cellulose was placed
at the tip of the objective to serve as an immersion fluid. The patient
was asked to focus on a fixation device to allow for the alignment of
the objective to the region of interest. Sections of the peripheral and
central cornea were imaged. Real-time images of all layers of the cornea
were detected through the use of a low-light camera and recorded. The
images were digitized and stored in computer memory.
Round hyper-reflective bodies seen with in vivo
confocal microscopy were defined as UFOs (Unidentified Full Objects).
Frames containing UFOs were selected and analyzed by a masked observer
(MP), to ascertain whether confocal images alone were sufficient to
formulate a correct diagnosis. The masked observer was then provided
with the color picture of the cornea and asked to re-assess his/her
previous diagnosis if needed.
Results
Fifteen out of the 30 patients presented Acanthamoeba
keratitis (AK); 4 conjunctival pigmented lesion; 3 Map-Dot- Fingerprint
keratopathy; 3 post-LASIK Diffuse Lamellar Keratitis (DLK); 2 fungal
keratitis; 2 epithelial in-growth and 1 corneal pigmented lesion. In vivo
confocal microscopy allowed for correct diagnoses in 22 cases (73%),
whereas in 8 the diagnosis was incorrect. Patients with AK and fungal
keratitis were correctly diagnosed. DLK patients were generically
diagnosed as having "corneal scarring" and subsequently correctly
diagnosed through examining the color picture. Out of the 8 misdiagnosed
cases, 7 were correctly diagnosed once the color picture of? the
cornea was provided. One patient affected by Map-Dot-fingerprint was
misdiagnosed as suffering from AK even ofter Examining the colour
picture (Table 1)(Figure 1&2).
Conclusion
In vivo confocal microscopy is a non-invasive examination that provides relevant information on corneal anatomy [5]Its role in the clinical setting has been the most described in the management of infectious keratitis [6].
Even if corneal scraping and biopsy remain the gold standard in the
micro biology diagnosis, IVCM may facilitate early diagnosis and the
initiation of targeted antimicrobial therapy. It is particularly
valuable in challenging cases such as contactlens- related AK [7]. Acanthamoebacysts, trophozoites and fungal hyphae can be identified by using IVCM directly [8]. In a prospective, doublemasked, observational study [9],
the sensitivity of IVCM in recognition of Acanthamoebacysts and fungal
elements was 88.3%, and specificity was 91.1%. As previously stated by
the American Academy of Ophthalmology which reported level II evidence
for the adjunctive role of IVCM in the diagnosis of AK [6,10].
Nevertheless, clinical pictures are instrumental in getting the correct
diagnosis. In our study, UFOs were mostly mis interpreted as
Acanthamoeba cysts, probably because that they are easily identified by
this tool thereby yielding a high rate of false positive findings. One
single image of IVCMis deemed insufficient if correct diagnoses are to
be made, as findings may well overlap in different diseases.
Nevertheless, when integrated with bio-microscopic findings, this tool
is essential if prompt, accurate and non-invasive diagnoses of corneal
disease are to be formulated.
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