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Spring-action Apparatus for Fixation of Eyeball (SAFE): a novel, cost-effective yet simple device for ophthalmic wet-lab training
  1. Seema Ramakrishnan1,
  2. Prabu Baskaran2,
  3. Romana Fazal3,
  4. Syed Mohammad Sulaiman4,
  5. Tiruvengada Krishnan1,
  6. Rengaraj Venkatesh5
  1. 1Department of Cornea and Refractive Services, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Pondicherry, India
  2. 2Department of Vitreo-Retina Services, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Pondicherry, India
  3. 3Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Pondicherry, India
  4. 4Instrument Maintenance Department, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Pondicherry, India
  5. 5Glaucoma Services, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Pondicherry, India
  1. Correspondence to Dr Seema Ramakrishnan, Department of Cornea and Refractive Services, Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Cuddalore Main Road, Thavalakuppam, Pondicherry 605007, India; drseemar{at}gmail.com

Abstract

Achieving a formed and firm eyeball which is stably fixed in a holding device is a major challenge of surgical wet-lab training. Our innovation, the ‘Spring-action Apparatus for Fixation of Eyeball (SAFE)’ is a robust, simple and economical device to solve this problem. It consists of a hollow iron cylinder to which a spring-action syringe is attached. The spring-action syringe generates vacuum and enables reliable fixation of a human or animal cadaveric eye on the iron cylinder. The rise in intraocular pressure due to vacuum fixation can be varied as per need or nature of surgery being practised. A mask-fixed version of this device is also designed to train surgeons for appropriate hand positioning. An experienced surgeon performed various surgeries including manual small incision cataract surgery (MSICS), phacoemulsification, laser in situ keratomileusis (LASIK), femtosecond LASIK docking, Descemet's stripping endothelial keratoplasty, deep anterior lamellar keratoplasty, penetrating keratoplasty and trabeculectomy on this device, while a trainee surgeon practised MSICS and wound suturing. Skill-appropriate comfort level was much higher with SAFE than with conventional globe holders for both surgeons. Due to its stability, pressure adjustability, portability, cost-efficiency and simplicity, we recommend SAFE as the basic equipment for every wet lab.

  • Medical Education
  • Eye (Globe)
  • Experimental &#8211 laboratory

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Introduction

The WHO estimates that currently 39 million people are blind globally and that this number is set to increase to 76 million by 2020 if no major interventions take place.1 India has nine ophthalmologists per million population, which is woefully inadequate for combating national challenges.2 It becomes imperative to train young ophthalmologists to meet this increasing demand.

Ophthalmic surgical training has evolved greatly from animal,3–5 hybrid6 ,7 and artificial8 ,9 practice eye models to virtual reality simulators10–12 and computer-based learning.13 Despite spending millions of dollars for simulators that circumvent wet labs, surgical skill learning on animal or human cadaveric eyes is still considered the closest approximation to real surgery, being particularly useful in low/middle-income countries with financial constraints.

Conventional globe holders are hollow metal or plastic cylindrical devices on which cadaveric practice eyes are fixed with wet cotton pieces7 or rubber band.5 Such devices have two major drawbacks: first, the eyeball keeps destabilising due to lack of a firm hold; second, the cadaveric globe tends to collapse due to low intraocular pressure (IOP). Collapsed globes have to be formed by injecting saline repeatedly into the vitreous cavity either through the pars plana or through the optic nerve stump.14 Attempting to acquire microsurgical skills in a constantly collapsing chamber of a ‘refusing to stay put’ eye is a nightmare for every surgical novice and a nuisance even for experienced surgeons trying newer surgical techniques.

We describe herein a novel device developed at our institute, the Spring-action Apparatus for Fixation of Eyeball (SAFE), constructed out of inexpensive everyday use materials, that tries to improvise on previous globe-holding designs.

Design

The prototype design consists of a hollow iron cylinder measuring 27 mm in height and 18 mm in internal diameter. The cylinder is closed at the base and has a small opening in its wall. This opening engages the tip of a disposable 5 mL spring-action syringe (figure 1A). Being spring action, the piston, once pressed and left, automatically returns to its original position sucking air into the barrel. When the eyeball is placed over the device, the spring-action syringe draws the eyeball into the cylinder due to the suction generated. The volume of initial displacement of the piston is proportional to the IOP rise in the fixed eyeball. Progressively increasing IOP ranging from 10 to over 60 mm Hg can be generated (figure 1C, D). This device fixes both human and animal eyes (goat, sheep and pig eyes) either at or just behind the equator (figure 2). The periocular fat or adnexal tissues need not be removed as they provide a snug fit. A range of five cylinders with internal diameter from 17 to 19 mm (gradation of 0.5 mm) was manufactured, though the 18 mm prototype was found suitable for most eyeballs.

Figure 1

(A) Prototype Spring-action Apparatus for Fixation of Eyeball (SAFE) device showing two components, the iron cylinder and the detachable spring-action syringe affixed. Arrow shows the location of the spring between the flange of the syringe barrel and the flange of the piston. (B) Modified SAFE device showing the mask-affixed version of the device with an eyeball mounted on it. (C) Perkin's tonometry being performed over the fixed eyeball. (D) Confirmation of high induced intraocular pressure by Schiotz tonometer.

Figure 2

(A) Collapsed globe before fixation. (B) Initiation of suction: white arrow shows spring-action piston being manually pushed; black arrow shows piston being displaced forward within the syringe barrel. (C) Activation of suction: piston is released, and it automatically returns back due to spring action. White arrow shows backward piston displacement. Note that the originally collapsed globe is formed well without any intravitreal injection of saline or balanced salt solution. (D) Fixed eyeball resists gravity on inverting the device.

Following ethics committee approval for use of cadaveric eyes, the prototype was used to perform manual small incision cataract surgery (MSICS), phacoemulsification, laser in situ keratomileusis (LASIK), femtosecond-LASIK docking, Descemet's stripping endothelial keratoplasty (DSEK), deep anterior lamellar keratoplasty (DALK), penetrating keratoplasty and trabeculectomy by an experienced surgeon. A trainee surgeon performed various steps of MSICS, phacoemulsification and wound suturing (table 1). Skill-appropriate comfort level for both surgeons was much higher with SAFE than with conventional globe holders (see online supplementary video).

Table 1

Procedurewise efficiency of the SAFE

Initial practice was done by placing the device on a styrofoam sheet with a circular central gutter that snugly fit the base of the SAFE (figure 1A). Later modification incorporated the device into the eye aperture of a human face mask for appropriate hand positioning during surgery (figure 1B). A mask offers better overall device stability than a trial head which has a rounded base that may destabilise while practising surgical steps.

Discussion

Stability and firmness of practice eyeball are vital for wet-lab training. Conventional eyeball holders offer no reliable fixating mechanism. Various synthetic,8 semisynthetic14 and biological eye models6 ,7 have been described for surgical practice, but their use is limited without an efficient stabilising device. The use of vacuum for fixing eyeballs has efficiently solved this problem. The Otto15 and Mohammadi16 devices use automated vacuum machines for globe stabilisation and are inherently expensive and less portable, whereas the SAFE uses minimal elements with a simple spring-action syringe to generate the desired vacuum reproducibly, making it highly cost-effective and portable. A commercially available product, the Mandell device, uses a conventional syringe connected to a plastic tube attached to the globe holder.17 The effort needed to pull the piston of a conventional syringe in order to generate adequate vacuum is significant. This effort is virtually eliminated by the spring-action syringe of the SAFE. Also, direct connection of the syringe tip to the cylinder eliminates additional tubing. Table 2 summarises and compares available literature on various globe-fixation devices.

Table 2

Concise summary of literature on eyeball-fixating devices

Our device gives excellent performance, especially during the practice of microkeratome pass (for LASIK or automated DSEK) and lamellar corneal dissection (for DALK and manual DSEK). Contrary to conventional devices that allow the globe to be easily lifted out of the holder by the suction ring, the SAFE prevents any globe dislodgement and facilitates smooth microkeratome pass (figure 3A, B). Lamellar corneal dissection, probably the most globe-destabilising procedure in the wet lab, is performed smoothly on the SAFE due to its dependable hold. In fact, the device has the potential to eliminate the use of an artificial anterior chamber (AAC) for DSEK donor preparation. Usually, this step is performed by mounting a donor corneoscleral button on an AAC which poses added expenditure to wet-lab practice. Instead, using a whole globe on the SAFE provides an identical experience during training. The original maskless version of the SAFE can even be held in the non-dominant hand such as the AAC while performing dissection with the dominant hand during manual DSEK, as is preferred by many surgeons including the author (figure 3C).

Figure 3

(A) Entire globe being lifted out of a conventional globe holder (along with cotton rolls used for fixation) by the suction ring used for microkeratome pass. (B) Globe firmly fixed to the Spring-action Apparatus for Fixation of Eyeball (SAFE) resists vacuum-assisted displacement by suction ring. (C) SAFE replaces an artificial anterior chamber for practice of lamellar corneal dissection in Descemet's stripping endothelial keratoplasty. SAFE being held in the non-dominant hand akin to an artificial anterior chamber.

In conclusion, we recommend this simple, robust and low-cost device as the basic equipment in wet labs. Multiple models can be assembled, one for each practice station, so that multiple trainees can simultaneously practice surgery, saving both time and money.

Acknowledgments

The authors acknowledge the participation of Dr Prashanth Gireesh and Ms S Vinitha, in addition to RF, one of the coauthors, who appear in the online supplementary video submitted to BJO.

References

Footnotes

  • Competing interests None declared.

  • Ethics approval Institutional Ethics Committee, Aravind Medical Research Foundation, No. 1 Anna Nagar, Madurai-625020, Tamil Nadu, India.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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