CME With Different Fluidic Parameters

• cystoid macular edema (CME) [ Time Frame: 3 months ] [ Designated as safety issue: Yes ]
  A > or = 30% increase in baseline central foveal thickness measaured by anterior segment OCT will be defined as having CME.
  
  

• macular thickness [ Time Frame: 1, 3 months ] [ Designated as safety issue: Yes ]
  macular thickness measured in 3 zones using the anterior segment OCT
  
  
• central corneal thickness (CCT) [ Time Frame: first post-operative day, ] [ Designated as safety issue: Yes ]
  CCT will be measured on the ultrasound pachymeter by a single experienced observer
  
  
• endothelial cell loss [ Time Frame: 6 months post-operative ] [ Designated as safety issue: Yes ]
  Endothelial cell loss will be measured using a specular microscope in the central area by a single technician
  
  
• anterior chamber inflammation [ Time Frame: 1 months ] [ Designated as safety issue: Yes ]
  it will be assessed on the slit lamp examination by a single experienced observer using the Hogan's criteria
  
  
• CORRECTED DISTANCE VISUAL ACUITY (CDVA) [ Time Frame: 3 months ] [ Designated as safety issue: Yes ]
  visual acuity (VA) of 20/40 or worse was defined as "clinically significant"
  
  

Several studies have shown the adverse impact of an increase in the IOP and IOP fluctuations that occur during anterior segment intervention on the posterior segment structures. In human volunteers with each incremental increase in IOP the systolic and diastolic flow velocities in the short posterior ciliary arteries decreased linearly. This implies that the normal healthy eye is not able to autoregulate to maintain posterior ciliary artery blood flow velocities in response to acute large elevations in IOP. Vascular insufficiency due to abnormal autoregulation has been proposed as a major factor in the development of glaucoma. 1

It has been postulated that IOP elevation during the LASIK procedure causes mechanical stress which may induce tangential stress on the posterior segment.2, 3 Some studies have reported that the increase in IOP damages the retinal ganglion cells causing visual field defects. Also sudden increases in IOP, although well tolerated may induce changes in the peripheral retina.4,5,6

Several reports propose the occurrence of macular hole, lacquer cracks and choroidal neovascular membranes following the LASIK procedure. 3 It has been observed that the rapidly fluctuating pressure variations may be detrimental, particularly in susceptible persons with compromised ocular blood flow. Rapid IOP changes across a 30-mm Hg range would be predicted to influence posterior segment blood vessels.

In a previous study we compared the impact of using high fluid parameters versus low fluidic parameters on real-time IOP measured during phacoemulsification. We found that using high parameters resulted in a higher absolute rise in IOP as well as higher fluctuations in the IOP when compared to low parameters. Clinically these higher fluctuations in IOP would translate in a higher chamber instability.

We hypothesize that although transient, the increased IOP that occurs during phacoemulsification when using high parameters could cause mechanical stress on the eye. These higher fluid parameters during phacoemulsification can predispose the eye to increased macular thickness.

To the best of our knowledge there are no published data on impact of IOP changes and fluctuation that are induced during cataract surgery on the macula. To investigate this further, we decided to study the impact of using high parameters (and thus, higher chamber instability) on macular thickness following surgery, in an otherwise uncomplicated surgery.