Gonak versus Balanced Salt Solution as a corneal wetting agent in cataract surgery

1
Gonak versus Balanced Salt Solution as a corneal
wetting agent in cataract surgery

• Jacob H. Chung, MDSuqin Guo, MD
• The Institute of Ophthalmology and Visual
  Science, UMDNJ-New Jersey Medical School

The authors have no financial interests to
disclose
Gonak is employed in this study for an
off-label use
2
Introduction

• Desiccation of the corneal surface prevents
  adequate visualization of intraocular structures
  during cataract surgery. Constant globe exposure
  necessitated by the surgery leads to drying of
  the corneal surface, degrading the quality of
  intraocular visualization.
• Traditional corneal wetting solutions
  included normal saline, lactated Ringers, and
  Plasma-Lyte. However, these posed a significant
  toxic risk to the corneal endothelium. Thus, the
  development of Balanced Salt Solution (BSS)
  provided a better safety profile due to a more
  physiologic electrolyte composition. BSS is now
  the standard corneal wetting agent in cataract
  surgery. However, the disadvantage of using BSS
  is that it requires frequent applications and
  therefore an assistant to irrigate the cornea. A
  more ideal corneal wetting solution would not
  have not only the features of safety, maintenance
  of surgical view, and cost-effectiveness, but
  also greater ease of use.

3
A novel solution

• Gonak (2.5 hydroxypropyl methylcellulose a.k.a.
  hypromellose, Akorn Pharmaceutical) is an optical
  coupling agent for contact lenses used in
  gonioscopy and commonly employed in
  vitreo-retinal surgery. Hypromellose is also
  marketed by other companies as Goniosol (for
  gonioscopy), Ocucoat (for intraocular injection
  as a viscoelastic) and in many artificial tear
  and hard contact lens solutions.
• Our hypothesis is that Gonak will perform as
  well as BSS in maintaining the optical clarity of
  the intraoperative view and better with regard to
  duration of effect.

4
Methods

• Candidates for small incision cataract
  extraction with intraocular lens implant were
  divided into two groups by virtue of the surgeon
  performing the operation.
• Group A, in which a single attending surgeon
  performed 90 of the cases, employed Gonak as the
  corneal wetting agent. A third year resident
  surgeon performed the other cases.
• Group B, in which third year resident
  surgeons performed, employed BSS as the corneal
  wetting agent.

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Methods (cont.)

• Preoperative and postoperative corneal clarity
  were measured subjectively by a single observer.
  An observer not involved in the surgery recorded
  the duration of surgery, number of applications
  of the irrigating solution, and the volume of
  solution used.
• Uncomplicated cases of cataract surgery with
  phaco-emulsification were selected for inclusion
  in the study. Exclusion criteria were a
  previous history of corneal disease (e.g., Fuchs)
  or corneal trauma (surgical or otherwise). Group
  A had 30 subjects and Group B had 16.

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Methods (cont.)

• Pre-surgical treatment was identical for both
  groups and included phenylephrine, tropicamide,
  cyclopentolate and a 5 betadine wash.
• A visible degradation of the corneal light
  reflex (Purkinje-Sanson image I) from the
  microscope was the main criterion for rewetting
  the cornea.

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Results
8
Discussion

• Gonak required very few applications per
  surgical case with a mean duration of effect of
  11.0 minutes- nine times longer than BSS. The
  average duration of effect of BSS was 1.2
  minutes, grossly similar to the findings of
  another study which found duration to be 2.0
  minutes (criteria for re-irrigation in that study
  are as much as needed).1
• Furthermore, due to optical properties
  behaving as a converging lens, a dollop of Gonak
  provides better visualization of the paracentesis
  and clear corneal wounds, also magnifying the
  image of the intraocular contents.

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Discussion (cont.)

• Preoperative and postoperative corneal clarity
  were the same, regardless of whether BSS or Gonak
  was used. The average length of the cases that
  employed Gonak were significantly shorter than
  those where BSS was used (due to surgeon
  experience level), so it is unknown if Gonak
  would pose a toxic risk to the corneal epithelium
  in cases which lasted much longer than those in
  this study.
• Aside from external surface considerations, risk
  to the corneal endothelium must be considered
  given the likelihood of ingress from a gaped
  corneal wound. Corneal endothelium can tolerate
  an osmolality range of 250 to 400 milliOsmoles/kg
  without significant endothelial breakdown.2
  Gonak is within this range of safety with an
  osmolality of 292 mOsm. 3 BSS has an osmolality
  of 298 mOsm.
• References
• 1. Arshinoff SA, Khoury E. HsS versus a blanced
  salt solution as a corneal wetting agent during
  routine cataract extraction
• and lens implantation. J Cataract Refract Surg
  1997 231221-1225.
• 2. Dick HB, Augustin AJ, Pfeiffer N. Osmolality
  of various viscoelastic substances Comparative
  study. J Cataract Refract
• Surg. 2000 261242-1246.
• 3. Akorn Laboratories, written communication.

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Conclusion

• Gonak is a superior alternative to BSS as a
  corneal wetting solution in routine small
  incision cataract surgery. Gonak offers similar
  clarity and has a much longer duration of effect,
  eliminating the need for a surgical assistant to
  rewet the cornea.