Journal of Pediatric Ophthalmology and Strabismus

Short Subjects 

Animal Model for Retinopathy of Prematurity Laser Surgery Training

W. Walker Motley III, MS, MD; Dema M. Atoum, MD

Abstract

Peripheral retinal laser ablation for high-risk retinopathy of prematurity (ROP) improves visual outcomes. Some pediatric ophthalmology fellows receive little exposure to this procedure. The authors identified and evaluated an animal teaching model that simulates peripheral retinal laser ablation in human infants with ROP. [J Pediatr Ophthalmol Strabismus. 2017;54:e47–e49.]

Abstract

Peripheral retinal laser ablation for high-risk retinopathy of prematurity (ROP) improves visual outcomes. Some pediatric ophthalmology fellows receive little exposure to this procedure. The authors identified and evaluated an animal teaching model that simulates peripheral retinal laser ablation in human infants with ROP. [J Pediatr Ophthalmol Strabismus. 2017;54:e47–e49.]

Introduction

Laser surgery for retinopathy of prematurity (ROP) can be a challenging procedure to learn. Most pediatric ophthalmology fellows in the United States participate in fewer than 5 ROP laser surgeries during their 1-year fellowships. Forty-six percent of recently graduated pediatric ophthalmologists believe that their ROP laser training during their respective fellowships was less than adequate in preparation for clinical practice.1 Of this group, 74% indicated that a wet laboratory training module would enhance ROP laser surgery skill acquisition.1 The purpose of the current study was to investigate use of the rabbit eye as an in vivo teaching model for ROP laser training.

Report

The current study was approved by the Institutional Animal Care and Use Committee of Cincinnati Children's Hospital Medical Center. One adult New Zealand white rabbit and one pigmented Dutch belted rabbit (Figure 1) underwent a peripheral retinal laser ablation procedure as an initial trial.

Adult Dutch belted rabbit under general endotracheal anesthesia.

Figure 1.

Adult Dutch belted rabbit under general endotracheal anesthesia.

The laser procedure was performed using the following method. A rabbit was placed under general anesthesia with endotracheal intubation. The pupils were dilated using two drops of cyclopentolate 1% and an eyelid speculum was inserted. To visualize the far peripheral retina and ora serrata, the globe was rotated and the sclera was depressed using a lens loop or disposable calcium alginate swab. A near-confluent pattern of photocoagulation was attempted using a diode red (810 nm) laser indirect ophthalmoscope (IRIDEX Corp., Mountain View, CA) and a 20- or 28-diopter condensing lens.

Five other faculty ophthalmologists who routinely perform ROP laser surgery were invited to test the simulation model and complete a survey. Costs of rabbits, veterinary anesthesia services, and supplies were tabulated.

The pupils of all rabbits dilated widely to between 7 and 8 mm with two doses of the cyclopentolate drops separated by 5 minutes. Pharmacologic mydriasis lasted at least 2 hours in all eyes. The rabbit fundus was found to have horizontally oriented myelinated nerve fibers and retinal vasculature radiating from the optic nerve head to the adjacent retina (Figure 2). The ora serrata could be identified by rotating the globe and depressing the sclera using a lens loop or calcium alginate swab. The globe was softer than that of a typical human infant, but intraocular pressure instruments were not available to make an objective measurement. The fundus of the New Zealand white rabbit was devoid of pigment. The fundus pigmentation of the Dutch belted rabbit was more similar to that of a human fundus.

Fundus photograph of the Dutch belted rabbit with horizontally oriented myelinated nerve fibers and retinal vessels emanating from the optic disk. The optic disk is not shown, but would be to the left of the myelinated nerve fibers shown. Laser photocoagulation spots produced with diode laser indirect ophthalmoscope are present in the retinal periphery.

Figure 2.

Fundus photograph of the Dutch belted rabbit with horizontally oriented myelinated nerve fibers and retinal vessels emanating from the optic disk. The optic disk is not shown, but would be to the left of the myelinated nerve fibers shown. Laser photocoagulation spots produced with diode laser indirect ophthalmoscope are present in the retinal periphery.

The procedure was first attempted on the fundus of the New Zealand white rabbit using a wide range of diode laser settings (energy: 200 to 2,000 mW; duration: 100 to 9,000 ms). However, little photocoagulation tissue effect was observed. Next, the procedure was attempted on the Dutch belted rabbit and photocoagulation was readily observed as demonstrated in Figures 23 using settings more typically used for ROP surgery in human infants (energy: 180 to 250 mW; duration: 100 ms).

Surgeon's view after applying laser treatment to the retinal periphery of the Dutch belted rabbit using the laser indirect ophthalmoscope.

Figure 3.

Surgeon's view after applying laser treatment to the retinal periphery of the Dutch belted rabbit using the laser indirect ophthalmoscope.

Total costs included $150 per rabbit, $1 per day boarding, and $15 per hour for the veterinary anesthesia service, which included anesthetic medication and supplies. The survey results of the 5 faculty ophthalmologists (4 pediatric ophthalmologists and 1 pediatric retinal specialist) who routinely perform ROP laser surgery are listed in Table 1. Each faculty ophthalmologist performed peripheral retinal laser photocoagulation on pigmented Dutch belted rabbits.

Results of Rabbit Teaching Model Trial Survey of 5 Faculty Ophthalmologists Who Routinely Perform ROP Laser Surgery

Table 1:

Results of Rabbit Teaching Model Trial Survey of 5 Faculty Ophthalmologists Who Routinely Perform ROP Laser Surgery

Discussion

Our initial selection of the adult rabbit eye for use as a training model was based on the similarity of the average adult rabbit globe axial length (15.12 mm) to the human premature infant globe axial length (15.27 to 16.65 mm at a gestational age of 32 to 41 weeks).2,3 The New Zealand white rabbit is a common species used in biomedical research and is the most readily available rabbit at our institution. We believe that visible photocoagulation burns could not be produced in the New Zealand white rabbit due to the absence of fundus pigment. The 810-nm wavelength diode laser energy is absorbed primarily by the retinal pigment epithelium and secondarily by choroid and retina.4 The fundus of the Dutch belted rabbit was pigmented and therefore yielded better photocoagulation results. We found that our initial attempt to perform retinal photocoagulation on the pigmented Dutch belted rabbit was successful with laser settings typically used for human eyes.

The additional teaching faculty who tested the pigmented Dutch belted rabbit model were uniformly in agreement that this model would be helpful to trainees and most believed that peripheral retinal laser ablation surgery would be easier to master on the rabbit than the human premature infant eye. The relative ease of the procedure performed on the rabbit eye is likely due to factors such as a widely dilated pupil, absence of tunica vasculosa lentis, and ease of scleral depression of the rabbit eye.

Instruction in and practice of the peripheral retinal ablation technique using an adult Dutch belted rabbit eye may be a good step for trainees to take early in fellowship to develop skills and confidence before attempting on a human infant eye. The fellow may practice using different power settings or methods of rotating the globe and depressing the sclera without the risk of harming a patient. Because most fellows are not exposed to many ROP procedures during fellowship, we believe that making use of a training model would permit the trainee to take better advantage of every ROP laser surgery case that presents during his or her 1-year fellowship. The teaching faculty may have additional confidence in permitting a fellow to perform the laser procedure on a patient after evaluating the fellow's skills with the training model.

References

  1. Bradley MH, Motley WW 3rd, . Pediatric ophthalmology fellowship training in laser ablation for retinopathy of prematurity. J AAPOS. 2012;16:539–542. doi:10.1016/j.jaapos.2012.08.012 [CrossRef]
  2. Bozkir G, Bozkir M, Dogan H, Aycan K, Güler B. Measurements of axial length and radius of corneal curvature in the rabbit eye. Acta Med Okayama. 1997;51:9–11.
  3. Laws DE, Haslett R, Ashby D, O'Brien C, Clark D. Axial length biometry in infants with retinopathy of prematurity. Eye (Lond). 1994;8:427–430. doi:10.1038/eye.1994.101 [CrossRef]
  4. Brancato R, Gobbi PG, Lattanzio R. Retinal photocoagulation with diode lasers. In: Fankhauser F, Kwasniewska S, eds. Lasers in Ophthalmology: Basic, Diagnostic and Surgical Aspects. Amsterdam, Netherlands: Kugler; 2003:241–254.

Results of Rabbit Teaching Model Trial Survey of 5 Faculty Ophthalmologists Who Routinely Perform ROP Laser Surgery

QuestionsResponses
How does the fundus view compare with that of a human infant?
  Very similar1
  Similar4
  Not very similar0
  Not similar at all0
Overall, how would you rate the rabbit model for laser training as compared with a human infant?
  Very similar0
  Similar5
  Not very similar0
  Not similar at all0
How difficult is it to perform the laser procedure on the model as compared with a human infant?
  More difficult0
  About the same1
  Less difficult2
  Much less difficult2
Do you think the rabbit model would provide trainees with useful experience before performing laser on human infants?
  Yes5
  No0
Authors

From Abrahamson Pediatric Eye Institute, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, Ohio.

The authors have no financial or proprietary interest in the materials presented herein.

Supported in part by a Challenge Grant from Research to Prevent Blindness, Inc. to the University of Cincinnati Department of Ophthalmology (James J. Augsburger, MD, Chairman).

Correspondence: W. Walker Motley, III, MS, MD, 3333 Burnet Avenue, MLC 4008, Department of Ophthalmology, University of Cincinnati, Cincinnati, OH 45229. E-mail: william.motley@cchmc.org

Received: March 14, 2017
Accepted: May 08, 2017
Posted Online: August 24, 2017

10.3928/01913913-20170531-06

Sign up to receive

Journal E-contents