ocular siderosis ( os ) is a severe sequel of retained iron - containing intraocular foreign body ( iofb ) .
a ferrous iofb undergoes dissociation resulting in the deposition of iron in the intraocular epithelial structures , notably the lens epithelium , iris and ciliary body epithelium , and the sensory retina , where it exerts a toxic effect on cellular enzyme systems , with resultant cell death .
pigmentary retinopathy followed by atrophy of the retina and retina pigment epithelium ( rpe ) can have a profound effect on vision and result in a subnormal electroretinogram ( erg ) .
management of os depends on the successful detection of an occult iofb as well as the determination of the need and optimum timing for its surgical removal [ 3 , 4 ] .
the aim of this study was to review the presentation , management , and outcome of this relatively rare disorder at our centre .
this was a retrospective study of os seen at the retina clinic from january 2009 to march 2015 .
the study was conducted in accordance with the declaration of helsinki and ethical approval was obtained from the institutional review board of the hospital .
eyes with a metallic iofb with clinical and/or erg features of os that underwent iofb removal were included in the study .
exclusion criteria included eyes with clinical features of os without an erg , eyes with os that did not undergo iofb removal , and eyes with erg features of os that had undergone iofb removal before presentation at our clinic .
the following information was then extracted from the case files and analysed : demographic data , duration of time from ocular injury to diagnosis of os , clinical findings , method of iofb localization , erg readings at presentation and at 6 months , surgical treatment , complications of treatment , and visual outcome .
all the patients had detailed ocular examination including visual acuity ( va ) assessment and refraction , slit lamp examination of the anterior segment , dilated indirect fundus examination , and intraocular pressure measurement .
radiological investigations including ocular ultrasonography with or without plain radiographs of the orbit and orbital computed tomography ( ct ) scan were done to localize the iofb .
ergs done at presentation and posttreatment were analysed . when carrying out the erg , the patient was first fully dilated and dark adapted for 20 minutes .
the patient was then asked to sit with his / her chin on the chin rest of the ganzfeld bowl with the eye being tested wide open .
a contact lens electrode was then placed on the cornea after instilling topical anaesthetic drops .
the right eye was tested first with the left occluded . a rod ( scotopic ) erg
the mixed cone - rod erg and oscillatory potentials were elicited by a single flash of red light at maximum intensity of 0 decibels .
to record the photopic responses from the cone system , the patient underwent 10 minutes of light adaptation by switching on the background light in the ganzfeld bowl .
the cone erg and 30  hz flicker erg were then recorded with a stimulus intensity of 0 decibels .
these were 8 males and 1 female with a mean age of 31.6 years ( range : 1747 years ) .
all the patients gave a history of sustaining ocular injury while hitting a piece of metal on metal .
trauma occurred from 3 months to 12 years ( mean : 2.9 years ) before the diagnosis of os was made at our clinic ( table 1 ) .
one patient ( case 6 ) had a history of previous intraocular surgery following trauma to the eye but an iofb was not found then .
best corrected visual acuity ( bcva ) at presentation ranged from 1/60 to 6/9 and the most common features of os were cataract and pigmentary retinopathy seen in 6 ( 67% ) and 4 ( 44% ) eyes , respectively . in four of the cases of cataract ,
the other 2 cases had a yellow - brown hue but a histological examination for the presence of iron particles in the lens epithelium was not done .
other features of os seen were heterochromia , anisocoria , and corneal endothelial dusting ( figure 1 ) .
posterior subcapsular cataract was the most common type of cataract encountered accounting for 5 ( 83% ) of the 6 cases of cataract .
other findings on ocular examination not related to siderosis included corneal scars , iris defects , iridodonesis , dislocated lens , and macular scar . the intraocular pressures were within normal limits in all the patients .
ocular ultrasonography was done in all the eyes with successful localization of the iofb in every case .
a plain radiograph of the orbit was performed in 4 patients and ct scan in 1 patient with an iofb demonstrated in each case .
surgical treatment included pars plana vitrectomy ( ppv ) for iofb removal alone ( 4 eyes ) or in combination with cataract extraction and intraocular lens ( iol ) implantation ( 5 eyes ) ( table 2 ) .
the erg was subnormal in all the eyes with 7 ( 78% ) eyes showing improvement following surgery ( table 2 ) .
seven ( 78% ) eyes gained 2 or more lines on va assessment after surgery .
complications encountered postoperatively included retinal detachment , retinal tears , and cataract progression . retinal detachment ( rd )
the first was at 2 months after iofb removal following which rd surgery was done with anatomical reattachment achieved .
multiple horse shoe tears were seen in case 9 and these were successfully barraged with laser .
case 2 had cataract progression and phacoemulsification with iol implantation was done at 1 year after iofb removal .
os is an uncommon condition and may appear from 18 days up to many years after a penetrating ocular injury with retention of a metallic foreign body .
the longest duration between the ocular injury and the diagnosis of os was 12 years in this series .
sneed and weingeist   and hope - ross et al .   reported shorter duration of 40 months and 24 months , respectively .
the time between ocular trauma and development of os may be related to the severity of intraocular toxic reactions .
this varies depending on the shape and size of the foreign body , its iron content , and the amount of time it remains within the eye .
heterochromia which had a similar incidence to cataract in other studies was , however , only documented in two patients in our series .
the aetiopathogenesis of secondary open - angle glaucoma related to os has often been ascribed to trabecular fibrosclerosis , probably because of the direct toxic effect of iron ions .
reported a case of an encapsulated iron - containing iofb situated on the retina of an 84-year - old man for 53 years , which did not lead to the expected os .
presentation with os months after an ocular injury may suggest that the iofb had been missed by the physician or ophthalmologist that attended to the patient following the ocular trauma . all primary care physicians as well as ophthalmologists should be aware of the possibility of a retained iofb in a penetrating ocular injury particularly when there is a history of high - velocity metallic injury .
it should be assumed that ocular injuries sustained in these types of settings potentially harbor an iofb until proven otherwise .
the diagnosis of an iofb is often made by direct visualization on slit lamp examination or ophthalmoscopy .
dilated fundus examination can reveal a foreign body in the vitreous or the retina if the media is not opaque .
if the suspected iofb is not seen , then further evaluation using imaging studies is necessary .
where an iofb is visualized , confirming the clinical finding with these investigations is also important as the iofbs may be multiple and may not all be picked up on clinical evaluation .
imaging studies for the detection of a metallic iofb include plain radiograph , ct scan , and ocular ultrasonography .
ultrasonography has been shown to be a very valuable tool that can augment the information obtained from other imaging modalities .
it should therefore be performed in all cases of os when an iofb is suspected .
ultrasound biomicroscopy of the anterior segment in eyes with secondary glaucoma may show an anomalous high reflectivity in the deep angular layers .
these alterations could be due to metallic particles imprisoned in the trabecular meshwork or indirectly on the consequent fibrotic reaction .
full - field erg is the most common means for detecting os and all patients should have this prior to surgical intervention .
iron retinotoxicity leads to a dysfunction of all the layers of the retina with more severe damage occurring in the inner retina than in the outer retina in the late stages of the disease . in the early phase , both the a - wave and the b - wave , though more commonly the former , can be transiently increased .
as siderosis progresses , the b - wave decreases , causing the b - wave / a - wave ratio to fall .
rod - dominated responses are predominantly affected as they have a greater susceptibility to iron toxicity compared to the cone system .
all the patients that had an erg done in these present series had electrophysiological features of siderosis with improvement in erg amplitudes following successful removal of the iofb in 7 patients .
improvement in erg with removal of an iofb has been documented by several authors [ 4 , 14 , 16 , 17 ] .
contrary to our finding , however , erg amplitudes remained subnormal in the series by hope - ross et al .
vision may be excellent in siderosis with erg amplitudes of up to 50% and complete reversal is possible following successful removal of the iofb in the early stages of the disease and with amplitudes of up to 40% [ 4 , 14 ] . over this limit
, macrophagic activity may be overwhelmed by the amount of iron load leading to direct cellular toxicity .
full - field erg also remains the reference follow - up exam in cases of delayed iofb removal and embedded iofb with likely difficulty with surgical removal and also following iofb removal [ 13 , 15 ] .
small iron particles can still be released at the inner retinal surface following surgical removal potentially inducing further toxicity .
os with subnormal erg has been reported 3 years after removal of a metallic iofb .
removal of the iofb should be strongly entertained in eyes with diminished ergs and a mobile foreign body in the vitreous or a nonencapsulated foreign body on the retina .
surgical technique for removal of the retained iofb is dependent on the site and nature of the iofb , the clarity of the lens , and whether or not the iofb is embedded in the retina .
the removal may be done via an external approach ( sclerotomy with large electromagnet ) or an internal approach ( vitrectomy followed by forceps or internal magnet use ) .
if the foreign body is located in the posterior vitreous or embedded in the retina , then a ppv is the preferred surgery .
iron - containing foreign bodies may lose their magnetic properties over time and a ppv with removal using intraocular forceps may be necessary .
a ppv also has the advantage of providing direct viewing and controlled removal of the iofb .
however , if the lens is clear and the foreign body is not embedded in the retina , then a sclerotomy with magnet extraction or intraocular forceps can be employed to extract the foreign body , particularly if it is located more anteriorly .
this lies between 25% reported by hope - ross and colleagues   and 79% reported by sneed and weingeist .
the visual potential in eyes with os may be excellent if the siderotic changes stabilize or improve and if the optic nerve and macula have not been injured .
pollack and oliver   reported an excellent visual outcome in a patient with os following iofb removal despite an abnormal erg .
removal of a cataract at the time of iofb removal may also lead to significant improvements in vision as was recorded in this series .
cases may not have been captured if they were inaccurately diagnosed or coded . in conclusion ,
a retained iron - containing iofb can manifest itself after several years with clinical and electrophysiological features of os .
careful clinical and radiological evaluation is essential following a penetrating ocular injury if this condition is to be prevented .
 
 purpose . 
 ocular siderosis ( os ) is a sight threatening complication of retained iron - containing intraocular foreign body ( iofb ) . 
 successful localization of the iofb and timely removal are crucial to its management . 
 the purpose of this study was to review the presentation , management , and outcome of os at our institution . 
 methods . 
 a retrospective case series of eyes with os that underwent iofb removal from january 2009 to march 2015 at our institution . results . 
 os was seen in 9 eyes of 9 patients during the study period . 
 there were 8 males and 1 female with an age range of 31.6 years . 
 an iofb was in all the eyes . 
 the most common features of siderosis were cataract and pigmentary retinopathy seen in 6 ( 67% ) and 4 ( 44% ) eyes , respectively . 
 electroretinogram ( erg ) readings were reduced in the 9 eyes . 
 the iofb was removed by pars plana vitrectomy in all the cases with improvement in erg amplitudes occurring postoperatively in 7 ( 78% ) eyes . 
 conclusion . 
 a retained iron - containing iofb can manifest itself after several years with features of os . 
 a careful clinical and radiologic evaluation is imperative in patients with history suggestive of penetrating ocular injury to rule out retained or occult iofb and thus prevent this catastrophic condition . 