Journal of Ophthalmology & Clinical Research Category: Clinical Type: Research Article
Neurophysiologic Studies in Metallosis Oculi
- Donald F Farrell1*
- 1 Neurology, EEG And Clinical Neurophysiology, University Of Washington School Of Medicine, Seattle, WA 98195, United States
*Corresponding Author:Donald F Farrell
Neurology, EEG And Clinical Neurophysiology, University Of Washington School Of Medicine, Seattle, WA 98195, United States
Received Date: Aug 05, 2015 Accepted Date: Oct 27, 2015 Published Date: Nov 10, 2015
Aim: To show that the Pattern reversal Electroretinogram (PERG) is more sensitive in establishing a diagnosis of metallosis oculi than the corneal full-field Electroretinogram (ERG). The ERG is however more useful in following the case than the PREG which may be absent.
Methods and material: Corneal full-field Electroretinograms (ERGs), Pattern reversal Electroretinograms (PERGs), were carried out on referred patients in a tertiary neurophysiologic laboratory. There were ten cases, all males, with a mean age of 42 years. The retained metal fragments were present from months to years with the longest being about 40 years. These studies were accomplished in order to determine which individuals would benefit from the surgical removal of the retained metal fragment.
Results: The PERG is the most sensitive test in establishing a diagnosis of a retained metal fragment, however, it may not be optimal for following the course of the illness.
Conclusion: The PERG is the most sensitive test currently available to establish a diagnosis of a retained metal fragment, but may not be of value if the patient has either glaucoma or the PERG shows an absent response. Other tests such as the ERG or PREP may be of greater value in following the course of the illness.
Sometimes, besides the rarity of the condition, FMH involves a large amount of fetal blood which can lead to important fetal morbidity and mortality . During pregnancy, clinical manifestations can be subtle and nonspecific which difficult the recognition of this condition. Antenatal suspicion of the diagnosis should occur when absent fetal movements is reported.
We describe this case to alert for this condition and the importance of maternal symptoms and newborn clinical findings. The prompt recognition and intervention is the key to the prognosis of this entity that can be fatal.
SUBJECTS AND METHODS
The period of time in which this study was accomplished covered a period of time when a corneal full-field electroretinogram was the principle diagnostic test and ended with the principle test being the Pattern reversal Electroretinogram (PERG), a test that turns out to be more sensitive. Six cases underwent testing with corneal full-field ERGs, three cases had both corneal full-field ERGs (ERG) and pattern reversal electroretinography. The ERG is carried out using a Burien-Allen corneal electrode to record responses (Figure 1-Burien-Allen corneal electrode). If a given patient cannot tolerate this electrode or if they have nystagmus a gold leaf electrode can be used instead. The gold leaf electrode records the responses without loss of amplitude or latency. A series of tests in both the dark adapted state with blue flash, red flash and white flash, measuring predominantly the rod function and progressing to cone function with 30 Hz white flicker then in the light adapted state, white flash, yellow-red and blue-green flash to measure cone function or subsets of cone function .
In actuality, only the blue flash in the dark adapted state is a pure rod test, cone oscillations are seen with red flash and a double a wave with a1 being of cone origin and a2 being of rod origin, the B wave is a mixture of the two to white flash. PERG testing uses the same recording electrode, but uses a checkerboard pattern with 30 minute visual angle as the stimulus. Six cases underwent PERG testing while three had both ERG and PERG testing.
Six cases underwent Pattern Reversal visual Evoked Potentials (PREPs), with one being symmetric and normal; the remainder showed various abnormalities in the affected eye with reduction in amplitude of the p100 being the most common abnormality, two of the abnormal cases showed no response at all. Abnormalities in the PERG include an amplitude difference between the eyes of 50 percent or greater. One case had simultaneous metallosis in one eye and glaucoma in both, with both eyes having abnormal PERGs. An Electro-Oculogram (EOG) was accomplished in 2 cases. A light peak to dark trough ratio method was used to establish whether the result was normal or abnormal. One was normal in both the normal and affected eye (2.41 OD and 2.93 OS) and one showed an abnormal response in the affected eye (1.36 OS and 2.25 OD). A normal value should be greater than 1.72 OU.
Pattern reversal Electroretinograms (PERGs) are more sensitive than corneal full-field flash Electroretinograms (ERGs) in the detection of retained metal fragments in the eye. The most common finding is an absent PERG in the affected eye.
By the time the ERG is abnormal significant damage has already been done to the retina. The PERG becomes abnormal to absent before any changes occur in the ERG itself, making it the superior test. One major complicating factor may be the co-existence of glaucoma which also affects the PERG [6,9], in that with glaucoma both eyes are likely to be affected. Retained metal fragments may also cause glaucoma, but that should only occur in the traumatized eye, not both.
Direct fundoscopic examination is likely to suggest the presence of ocular metallosis. Two major changes are likely, 1) the presence of an encapsulated fragment or 2) siderosis, or a generalized staining of the ocular contents.
Intra-ocular pressure should then be measured and if the unaffected eye is normal, then a PERG should be obtained to confirm the existence of a retained metal fragment. Once confirmed the retained metal fragment should be removed to prevent any further visual loss. The PERG response may be absent early in the course so may not be of great value in following cases to determine if progression is occurring. If progression is suspected then a corneal full-field flash ERG may be used to follow the course of the illness. One additional test may be of value in following progression, but it has not been studied. This test is the Pattern Reversal Evoked Potential (PREPs). Five cases in this current study showed abnormal PREPs. In all cases the amplitude of the p100 was reduced reflecting the involvement of the ganglion cell layer, the origin of the optic nerve in the eye.
The proper management of a traumatic retained metal fragment may require the use of several tests. Ultrasound biomicroscopy appears to be an excellent method for the identification and localization of acute metal fragment within the first few days of injury. The PERG is sensitive in the identification of retained metal fragments, but when the response is absent may be of no value in following those cases that may later show progression. The corneal full-field flash ERG still has some value in following the course of the disorder and PREPs may also be of value in following a given case.
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Citation:Farrell DF (2015) Neurophysiologic Studies in Metallosis Oculi. J Ophthalmic Clin Res 2: 015.
Copyright: © 2015 Donald F Farrell, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.