Hollis Nomogram for the Nidek Excimer Laser

The Nidek uses an opening slot for myopic astigmatism, and an opening iris for myopia. The input to the laser is in minus cylinder. The laser uses a rotating disk for hyperopic astigmatism, combined with an opening slot. The same rotating disc if used to correct hyperopia. A second disk is used with each hyperopic treatment to expand the optical zone. With hyperopia the input into the laser is in plus cylinder form, different than for myopia. I. never found the look up table from Nidek to be helpful. I quickly learned that the laser overcorrects myopia and under corrects astigmatism. The nomograms are totally different for myopia and astigmatism. Hyperopia tends to overcorrect for both hyperopia and hyperopic astigmatism. I like the Nidek better than any other laser for these treatments. There is no age adjustment in hyperopia.

  • Prescription
  • Adjustment
  • +1.00
  • -0%
  • 1.50
  • -4%
  • 2.00
  • -8%
  • 2.50
  • -12%
  • 3.00
  • -16%
  • 3.50
  • -20%
  • 4.00
  • -24%
  • 4.50
  • -28%
  • 5.00
  • -32%
  • 5.50
  • -36%
  • 6.00
  • -40%
  •  
  •  


Since the rotary astigmatism treatment is just half of a hyperopia treatment, these adjustments are also made for astigmatism.

For astigmatism using the opening slot, I add 20 % to the error, and there is coupling, so I subtract 1/3 of the new new astigmatism reading from the sphere.

Example: -1.00-1.00 any axis becomes -0.60 -1.20 any axis.

I still find this yields a 28 % overcorrection on the sphere, so I reduce the sphere by 28%. Since the Nidek does not correct less than a half dioptor of myopia or astigmatism, I just do 2/3 of the treatment, don’t do it all. I went from a Nidek to an Allegretto and back to a Nidek lasers. The primary difference was that the Allegretto had better 1st day vision than the Nidek. Since I am reducing myopic correction by 28%, the Nidek now gives first day postoperative vision equal to the Allegretto. At a month, the vision was the same. AN OVERCORRECTION SEEMS TO TRIGGER A MORE ACTIVE EPITHELIAL BUILDUP AND REVERSES AN OVERCORRECTION. It would be better to get it right the first time.

There is also an age overcorrection with myopia. I subtract an additional 8% above age 45 and another 8% above 60 years of age. ON SOMEONE OVER 60 YEARS, on the above -0.60, I would subtract an additional 44%. 28+8+8=44. -0.60 -44%= -0.029.

For hyperopia I use the full cycloplegic refraction. I use no age adjustments with hyperopia.

For monovision, I add +1.50 to the cycloplegic prescription, typically in the non-dominant eye. An interesting way of testing for the dominant eye is to open the phoropter with the final Rx and have the patient look at the chart. Put a loose plus +1.50 lens over the right eye and ask if it bothers the patient. Then place it over the other eye. The one it bothers the most is the dominant eye, the one it bothers the least is the non-dominant one. 1% of right hand men are left eye dominant, 60% of right handed women are left eye dominant. If you find a woman under 42 with near vision problems, you will find she had a hysterectomy 7 or more years ago, and it does not matter if the ovaries are removed or not. It is the uterus.

I use mitomicin for 15 seconds on all hyperopic PRK cases and on myopia above -4.00..

PTK with the Nidek

The Nidek is excellent for PTK. I prefer to use it to remove the epithelium in PTK cases. This takes advantage of the modulating effect of the epithelium which thickens to fill in low spots, and thins to reduce the hight spots. I set the laser at 5 to 7 mm in a circle and shoot the epithelium with the lights off. We set the laser at100 microns. We usually do not use it all anyway. The epithelium glows when struck by the excimer and turns black when the stroma is reached. Very .little tissue is removed, just the high spots. The breakthrough usually occurs at the high spots on the topography. I have had problem patients recover 20/15 vision from 20/60 best corrected with this procedure. Until topography guided lasik/PRK is approved by our FDA, this is the best option we have to solve problems. Our government requires us to give care with our hands tied behind us. I remember 14 years ago that Dr. Margarite McDonald was saying that one day the topographer and the laser would be linked. I believe this approval has been held up to allow politically connected VisX to make more money before it is approved. All government does is choose winners and losers based on political reasons. I have accomplished PTK with the Allegretto. I will share the parameters with anyone requesting them. Vision is very slow to recover with PTK. The larger the optical zone the slower the recovery. I have had 5 mm PTK’s recover in 2 weeks. I find that the PTK corrects about 0.75 of myopia, or induces of 0.75 of hyperopia.

PTK/PRK

The Nidek is perfect for removing the epithelium with the laser and then doing PRK. The positive effect is to smooth the cornea and improve vision, if needed. It only smooth the cornea if it is needed. It does not induce irregularity of the cornea. When the PTK is combined with PRK, we get a smoothing of the cornea and an improvement of vision, combined with the PRK correction. Dr. Cantu of Mexico has been doing this for years. Patients are afraid of blades, so this is bladeless Lasek, or No touch PRK.

I do PTK at 7.5 mm for 100 microns for a hyperope, quitting when the high spots are gone (50% removal). I usually use 5.5 mm at 100 microns for myopic correction. This is usually less than the full 100 microns. For a myope with a small pupil, I have used a 5 mm oz for PTK. They recover very quickly. I figure the PTK has added plus 0.75 to the correction. I then take that 0.75 diopter from the myopic correction and use all the nomogram adjustments. For hyperopia, I add 1 diopter to the plus because of the +0.75 from the PTK. I add another +0.50 because of the remaining epithelium that is always left in the periphery after PTK. I believe this is caused by the laser beam hitting at a 45 degree angle in the periphery. Much of the energy is deflected and so therefore epithelium is left in the periphery.

Bifocle Cornea

The Nidek is the only laser appropriate to create the bifocal cornea using the center for distance. Small myopia optical zones of 4 or 4.5, can be used, since the are beyond that diameter is being treated with a hyperopia treatment. Large myopic optical zones are counterproductive since you are treating the 4 to 5 mm with both treatments, and making the contours less than optimal for the dual vision to occur. A monovision near eye typically sees 20/70. With the bifocal cornea, I have achieved 20/20 distance in the one eye with 20/40 near. The near eye is 20/30 distance and 20/25 near. With both eyes open, the patients that do not adjust to monovision, easily adjust to this.

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