Removal of a retained intraocular foreign body (IOFB) is one of the very few ophthalmic emergencies which can cause a nightmare like situation at times even for an experienced surgeon. Careful evaluation and meticulous planning can help us achieve good anatomical and functional outcomes in these complex scenarios.

It is extremely important to choose the right instrument for removal of IOFB based on its size, shape & nature. This will minimize any unnecessary prolonged maneuvers and also minimize trauma to the surrounding tissues. Here, we will focus on instrumentation that are available and needed for various posterior segment IOFB.

IOFB extraction techniques vary according to factors such as the location, content, magnetic properties, and extent of local damage.

There are two crucial steps in IOFB removal 1) Lifting the foreign body 2) Removal of foreign body.

An important decision to be made while approaching an IOFB is to determine its nature, magnetic or non-magnetic.

Endomagnets:

If we are dealing with a magnetic IOFB, it can be lifted easily using endomagnets (figure 1) that are commercially available in various gauges to accomplish this step ⁽²⁾.

Figure 1 Endomagnet made of titanium body available in 18G , 20G and 23G

Once lifted, IOFB can be brought to the anterior vitreous face (phakic) or pupillary area (aphakic) and removal of the IOFB using a second instrument is performed either through a large sclerotomy (phakic eyes, size of IOFB < 3-4 mm) or through limbal approach (aphakic eyes, size of IOFB > 3- 4 mm). If the size of IOFB is significantly large necessitating a very large sclerotomy wound for removal, a surgeon may decide on even performing clear lens extraction to facilitate IOFB removal through limbal route.

Usually, endo magnets are not helpful in removing the IOFB through the sclerotomy or limbal route. The magnetic force helps only to hold the IOFB in vitreous medium where there is no counter traction. While negotiating through the exit wound, IOFB would invariably fall off if attempted to remove using the endomagnet itself. Intraocular forceps are needed to accomplish this step.

Intraocular forceps:

Intraocular forceps are needed to lift nonmagnetic IOFB, remove both magnetic and non-magnetic IOFB.

Diamond coated all-purpose foreign body forceps:⁽³⁾

This was probably the first forceps designed exclusively for IOFB removal. It was introduced by Robert Machemer in 1981. It has two diamond dusted jaws protruding from a stainless-steel tube. The jaws can be opened by sliding a knob located on the handle and it can be automatically closed by leaving the knob due to the spring mechanism (figure 2). Because of the self-closing mechanism, tiring of fingers after grasping the foreign body does not occur.

Figure 2: Two-jaw foreign-body forceps. The jaws are opened by sliding the control backwards. They close automatically by spring action.

Snare devices ^{(4 -7)}:

The majority of the small IOFBs can be removed by using either a forceps or a combination of endomagnet and forceps if IOFB is magnetic. However, unique devices and strategies are needed for hard-to-extract large IOFBs, all the more if the IOFB is nonmagnetic. ^(8,9,10)

In 2003, DIY (do it yourself) snare device ^(4,7) was suggested which comprises a flexible loop made of 7-0 polypropylene suture (Figure: 3A & 3B). This loop enables for a delicate grabbing of foreign bodies without exerting pressure on the retina. The snare action ensures a consistent and simultaneous grasp on all points of contact with the foreign body. The applied circumferential power is sufficient to ensure that the IOFB does not slip. However, the suture may be difficult to string and can snap if the IOFB is heavy. It has a learning curve too and can take multiple attempts to engage the IOFB in snare.

Figure 3A & 3B: Heated metal nail to create two holes in the stem of a 1-mL syringe B : After threading the 5-0 nylon suture through the 20-gauge needle, pull it through the syringe stem holes, and knot it to the plunger. (4,7)

In the year 2006, Eckardt introduced memory snare ⁽⁶⁾ which is an upgraded version of suture snare. It consists of a handpiece and 20-gauge tube holding the memory Snare. Due to wire memory, as the snare advances it deploys at 80° outside the tube with maximum diameter of 3 mm* 3.5 mm and tightens when pulled back (Figure 4A & 4B). Unlike a simple snare, this tool does not need to be guided under an IOFB lying on the retina. Instead, it can be placed parallel to the retina due to its angled configuration. It can grasp foreign body close to its alignment. This addresses the issue of difficulty in removing linear foreign bodies with conventional snare techniques. However, it is difficult to use for heavy IOFBs.

Figure 4: A, Memory Snare withdrawn inside the tube. B. Memory Snare deployed at 80° outside the tube.

Nitinol Basket Forceps:

In 1990 Pulido et al used a ureteric stone extractor for removal of glass IOFB ⁽⁸⁾. Later in 2019 Durrani et al used tipless Nitinol basket for the removal of IOFB in an eye with posterior staphyloma and speculated that it can be useful in removal of IOFB from eyes with high axial length ⁽⁹⁾. Nitinol stone basket NSB (10) is specifically designed for extracting stones in the ureter and renal calyces by direct visualization through endoscope. Though its tipless design makes it free from retinal damage and can be easily fit in 23 gauge port, Its long wire and need of skilled assistants to operate make it difficult to use frequently (Figure 5).

Figure :5 Nitinol Stone Basket (NSB): Retractable 4-wire basket with a 1.9 French stiff tip (23-gauge), measuring up to 12mm wide and 18mm long with handle at the other end of the tube (11)

In 2017, Acar designed a nitinol basket forceps exclusively for IOFB removal ⁽¹¹⁾ This design was inspired by previously reported suture snare principle ⁽¹²⁾ which was done by Acar himself in 2009. It features two extendable loops at its end, positioned perpendicular to each other. These loops are specifically designed to effectively grasp and capture intraocular foreign bodies (IOFBs), as well as dislocated lens and intraocular lens. This 20-gauge reusable forceps has two extendable metal loops perpendicular to each other. A sliding knob on the handle is used to extend the loops and retract the same after grasping the IOFB. The loops are made of nitinol material which has good memory and elasticity. The loops can expand up to 14 mm vertically and 8 mm horizontally (Figure 6). Acar forceps require finger pressure to grasp the IOFB till it is removed. The limitation of this basket forceps is that it will be very difficult to remove linear foreign bodies. The linear foreign bodies will have to be grasped perpendicular to the shaft of these forceps and might require relatively large sclerotomy.

Figure 6: Acar IOFB forceps with extendable 2 metal loops perpendicular to each other at its tip with button at the center of the handle which can be There is a sliding button at slide forward to enlarge and slide backward to decrease the diameter of the loops according to the size of the IOFB to be grasped. (12)

The claw Forceps:⁽¹³⁾

The IOFB claw forceps was introduced by Maneesh Bapayee in 2018. His design was inspired by the Dormia basket concept, commonly utilized in urology for extracting proximal ureteric stones. It has four nitinol wire prongs lodged in a 19 gauge stainless steel shaft. Sliding knob on the titanium handle is used to extend the nitinol prongs which open like a claw and can grasp the IOFB and retract it towards the shaft by adjusting the knob. The prongs open to 14mm vertically and 8 mm horizontally. It has a shaft length of 27 mm with outer diameter of 1.2mm and 0.9mm of inner diameter (Figure 7A, B & C). It is effective for extracting various types of intraocular foreign bodies, including smooth spherical ones and large irregular ones, providing a strong grip on the IOFB with minimal slippage. The claw forceps requires finger pressure to grasp the IOFB till it is removed.

Figure 7: A. The claw forceps with shaft that houses the prong and knob housed at the handle B & C showing widest extent and length of the shaft and prong

Locking Forceps:

This is designed and developed by the authors in collaboration with Epsilon for removing all IOFB especially for hard to extract large nonmagnetic IOFB. The outer diameter of the shaft is 1 mm and can open up to 16 mm (Figure 8 A & B):

Figure 8 A & B Locking forceps showing 1mm shaft which can open up to 16 mm

This forceps has a locking mechanism because of its cross action. The tongs open up when the handle is digitally pressed and closes when pressure is released. When the tongs close, the IOFB gets locked and there is no further finger pressure needed to hold the IOFB and remove the IOFB through the sclerotomy or anterior route.

Conclusion:

Intraocular foreign body removal is an art where a surgeon needs to think like an artisan equipped with various tools and apply based on the foreign body’s nature, size and location. There is no single instrument that can handle all types of foreign bodies. Customized approach is the best way to deal with IOFB.

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