|Exposing the LASIK Scam
|Dr. Steven Schallhorn's study
|Page 2 of 2|
|Author:||Broken Eyes [ Fri Feb 03, 2006 2:54 am ]|
In the first post on this thread, Bill mentioned a 10-year old PRK study conducted by Schallhorn.
http://www.ncbi.nlm.nih.gov/entrez/quer ... query_hl=1
Ophthalmology. 1996 Jan;103(1):5-22.
Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel.
Schallhorn SC, Blanton CL, Kaupp SE, Sutphin J, Gordon M, Goforth H Jr, Butler FK Jr.
Department of Ophthalomology and Clinical Investigation, Naval Medical Center, San Diego, CA, USA.
PURPOSE: To evaluate the safety, efficacy, and quality of vision after photorefractive keratectomy (PRK) in active-duty military personnel.
METHODS: Photorefractive keratectomy (6.0-mm ablation zone) was performed on 30 navy/marine personnel(-2.00 to -5.50 diopters [D]; mean, -3.35 D). Glare disability was assessed with a patient questionnaire and measurements of intraocular light scatter and near contrast acuity with glare.
RESULTS: At 1 year, all 30 patients had 20/20 or better uncorrected visual acuity with no loss of best-corrected vision. By cycloplegic refraction, 53% (16/30) of patients were within +/- 0.50 D of emmetropia and 87% (26/30) were within +/- 1.00 D. The refraction (mean +/- standard deviation) was +0.45 +/- 0.56 D (range, -1.00 to 1.63 D). Four patients (13%) had an overcorrection of more than 1 D. Glare testing in the early (1 month) postoperative period demonstrated increased intraocular light scatter (P<0.01) and reduced contrast acuity (with and without glare, (P<0.01). These glare measurements statistically returned to preoperative levels by 3 months (undilated) and 12 months (dilated) postoperatively. Two patients reported moderate to severe visual symptoms (glare, halo, night vision) worsened by PRK. One patient had a decrease in the quality of night vision severe enough to decline treatment in the fellow eye. Intraocular light scatter was increased significantly (>2S D) in this patient after the procedure.
CONCLUSIONS: Photorefractive keratectomy reduced myopia and improved the uncorrected vision acuity of all patients in this study. Refinement of the ablation algorithm is needed to decrease the incidence of hyperopia. Glare disability appears to be a transient event after PRK. However, a prolonged reduction in the quality of vision at night was observed in one patient and requires further study.
Are you wondering how large the pupils were of the one patient with severe night vision disturbance who refused treatment in the 2nd eye? Here's an excerpt from the full text:
"One patient had poor night vision after PRK and elected not to have the procedure performed in the second eye. Preoperatively, refraction was -5.50 D spherical and at 12 months it was -1.00 +.50 D axis with a trace of central haze. When viewing a point light source in a dimmed room, the patient described annular mist surrounding the light in the surgical eye. There was no mist surrounding the light when viewed by the nonsurgical eye. The pupil diameter under dim lighting (10 lux) was 7 mm (study mean, 6.3 +/- 1.01 mm). A trial of full correction (-1.00 +.50 axis 85) and over-minused (-2.00 +.50 axis 085) spectacles failed to alleviate the nighttime symptoms. However, the nighttime visual problems improved with rigid gas-permeable contact lenses and resolved with low-dose pilocarpine (0.125%)."
Referring to this patient in the abstract, Dr. Schallhorn said this patient's night vision problem "requires further study". What more do you need to know? The patient is seeing through focused and unfocused cornea when his pupils dilate at night. How much study does that require?
Immediately following this article is a commentary by Leo J. Maguire, MD.
"If the mission is to give all troops 20/20 uncorrected photopic visual acuity 1 year after surgery, then the mission is accomplished-- at least in the first eyes of these two Navy SEALs and 28 other Navy personnel. If the mission is to provide a service that consistently preserves optical quality and accurately corrects refractive error, then we find casualties among the volunteers and some information missing in action".
"It shows a high incidence of night vision symptoms in contact lens wearers and a statistically significant overall improvement in subjective assessment of night-driving tasks, halos, and glare among contact lens wearers. Unfortunately, we also have the postoperative minority with severe halos, severe glare, and disabling night vision -- all in a group with relatively low myopia. One can always discontinue contact lenses, but refractive surgery is forever."
"The results are mixed. The surgery is successful in the majority of patients, but the laser still takes prisoners. Upgrades in laser design and study protocols may eliminate these problems. Until then, the Navy should maintain the regulatory guard, and continue to gather intelligence".
Apparently the Navy is still lacking reliable intelligence.
So now you know. 10 years ago a colleague of Dr. Schallhorn performed PRK with a 6mm zone on a patient with 7mm pupils (at 10 lux!) and left him with severe night vision disturbances.
Schallhorn prescribed pilocarpine to reduce the size of the patient's pupils which resolved his night-time visual problems.
10 years later Schallhorn still hasn't figure out the importance of pupil size. You just have to wonder how many patients he has harmed.
I'm guessing the aberrometer he uses only measures to 6 or 6.5 mm. As long as he mismeasures pupils, mixes apples with oranges (pure sphere with astigmatic treatments, and low myopes with high myopes), uses poorly designed "surveys" that don't take severity into account, and doesn't do any objective tests at the size of the scotopic pupil, he will never get it right.
|Author:||Bill [ Sat Mar 04, 2006 1:35 pm ]|
Here's another example of Schallhorn talking out of both sides of his mouth regarding the importance of pupil size.
http://www.eyeworld.org/article.php?sid ... y=alphagan
Steven C. Schallhorn, MD: I tried over-minusing a little in a young patient for night driving glasses - night myopia - which can induce a little accommodation that they can easily handle, such as -0.5 D, and it constricts their pupils too.
|Author:||Broken Eyes [ Tue May 30, 2006 3:06 pm ]|
http://www.escrs.org/eurotimes/August20 ... lement.asp
In 2002, Schallhorn comments on his knowledge of vision and higher order aberrations:
"There is much we don't understand about higher order aberrations and how they are related to vision... [snip]"
Oh, but wait, in 2003 he has become an expert:
http://www.fda.gov/ohrms/dockets/ac/03/ ... 3991t1.htm
Now, my area of expertise and what we've studied to a great extent, deals with the quality of vision after refractive surgery and that's really what I'd like to spend the rest of the time talking about.
|Author:||Broken Eyes [ Thu Aug 16, 2007 1:31 am ]|
Also see Letter to the Editor by Salz, Boxer Wachler, Trattler, and Holladay in Ophthalmology August 2004.
|Author:||Broken Eyes [ Tue Sep 04, 2007 1:16 am ]|
FOOD AND DRUG ADMINISTRATION
MEDICAL DEVICES ADVISORY COMMITTEE
OPHTHALMIC DEVICES ADVISORY PANEL
OCTOBER 3, 2003
STEVEN C. SCHALLHORN, M.D.:
Patients who have high levels of preop myopia had a significant decrease in the night-driving performance.
It is well-known that the deeper the ablation (the higher the pre-op myopia), the greater the induction of spherical aberrations. This is due to the angle of incidence of the laser on the cornea, with the rays striking the center of the cornea ablating more tissue than the rays striking the peripheral slope of the cornea. All factors being equal such as pupil size and laser treatment diameter, a -9 myope will have higher post-op spherical aberrations (night vision disturbances) than a -2 myope.
The range of myopia in this study was -2.88 to -9.25D. Myopia varied across the range of pupil sizes.
If you treat patient-A with a medium pupil for -9.25 myopia, and patient-B with a large pupil for -3.00 myopia, the depth of the ablation has skewed the conclusions for night vision disturbances because medium-pupil patient-A is likely complaining of visual aberrations at night.
What kind of peer-review allowed this study to be published? This study is a joke. Even Schallhorn admits that high myopes are at high risk for night vision disturbances.
Schallhorn makes himself look like a moron.
|Author:||Bill [ Sat Sep 15, 2007 7:40 pm ]|
The following is a review of the study published by Steven C. Schallhorn, et al: Pupil size and quality of vision after LASIK.
Ophthalmology. 2003 Aug;110(8):1606-14.
I. Insufficient number of large pupil patients to make any valid conclusions on the issue of pupil size and night vision disturbances.
100 patients (200 eyes) were enrolled in the study: Schallhorn classified pupils sizes as follows:
Small 5mm or smaller 31 patients
Medium 5.5 and 6.0 53 patients
Large 6.5mm or larger 15 patients
(1 patient?s pupils were not measured)
The large pupil group was comprised of only 15 patients:
6.5mm pupils 5 patients
7.0mm pupils 8 patients
7.5mm pupils 1 patient
8.0mm pupils 1 patient
Only 8 large pupil patients (of the original 15) completed the endpoint (6 month) questionnaire. Figure 4 of the study (page 1611) shows missing data for the only 8mm pupil patient.
This study tells us nothing about patients with very large pupils.
II. Loss to follow-up is too great to validate study conclusions.
Of the 100 patients enrolled, only 66 patients completed the endpoint (6 month questionnaire). We are left to wonder about 1/3 of the patients enrolled in the study.
III. Schallhorn used optical zones of varying sizes across the range of pupil sizes.
110 eyes 6.0mm ablation spherical ablation
90 eyes elliptical ablation ranging from 6.0 x 4.5 to 6.0 x 5.5 or greater
This is a major flaw of the study. In order to make any valid conclusions about the correlation of pupil size and night vision disturbances after LASIK, the refractive error and the ablation zone diameter should have been consistent across the range of pupil sizes.
IV. Methodology of obtaining pupil sizes is questionable.
Schallhorn states that pupil measurements were obtained at <5 lux. Scotopic is .04 lux. High mesopic is 4 lux. Pupil measurements vary greatly between scotopic and mesopic. The lighting conditions should have been rigorously controlled.
How was the room illumination measured? Schallhorn does not tell us in the study.
Schallhorn does not state if he controlled the duration of dark-adaption. Patients should be allowed to dark-adapt for 5 minutes.
Did Schallhorn control for interobserver variability of pupil measurements? We don?t know.
If there are flaws in the methodology of measuring the patients? pupils, then the entire study is meaningless because we really don?t know the true pupil sizes of the patients enrolled in this study.
V. Schallhorn enrolled patients of varying degrees of myopia across the range of pupil sizes.
Schallhorn himself has stated repeatedly that high myopia is a risk factor for night vision disturbances after LASIK. The range of myopia in the study is -2.88D to -9.25D. It is well known that the higher the myopia, the smaller the effective optical zone. The refractive error, as well as the size of the optical zone, should be consistent across the range of pupil sizes in order to draw any valid conclusion about the role of pupil size in quality of vision after LASIK.
VI. The questionnaire designed by Schallhorn is faulty. No objective tests were used to measure visual aberrations.
Schallhorn relied on subjective questionnaires instead of objective measures. We can only speculate what the outcome of the study would be if objective testing, which was available, had been used to assess visual quality. Schallhorn admits that patients with large pupils had more visual symptoms in the early postoperative period. He also admits that as time passes, patients tend to become more tolerant and complain less. This does not mean their vision improved, it simply means that patients tend to get used to their ?new vision? after the second eye is treated when they no longer have a good eye for comparison.
Schallhorn misuses the terms ?glare? and ?haze?. This surely would have caused some confusion for the study participants and resulted in errors in the reporting of symptoms.
Schallhorn asked about the frequency of visual symptoms but did not ask about the severity of visual symptoms. If a small pupil patient saw small halos at night ?most of the time? which did not affect the patient?s quality of life, this patient?s response was considered the same as a large pupil patient who saw massive halos at night ?most of the time? which were life-altering. Visual aberrations must be measured in order to draw any valid conclusions.
VII. Schallhorn did not control for residual myopia and astigmatism.
Another major flaw in this study is the lack of control for residual refractive error. It is well known that patients with residual refractive errors will experience visual symptoms at night. A patient with small or medium pupils with residual myopia and astigmatism will have night-time visual symptoms. Schallhorn states, ?Some patients with small pupils have these problems all the time?, but he fails to provide any explanation.
This study has numerous flaws and one cannot draw any solid conclusions from it about the role of pupil size and quality of vision after LASIK.
|Author:||Broken Eyes [ Mon Oct 15, 2007 8:37 pm ]|
Review of Ophthalmology
Vol. No: 13:12Issue: 12/1/2006
More on the Challenges Of Pupil Size & LASIK
James J. Salz, MD
This raises the philosophical question: Should we as refractive surgeons, recommending an elective procedure to reduce the need for glasses, be too cautious or less cautious? Dr. Shapiro evidently feels we can be less cautious in this regard and uses his reading of the literature to support his position.
He talks about the large, excellent studies of Schallhorn and Pop. Let?s take a close look at the ?large? Schallhorn study. The article by Schallhorn1 in 2003 on 100 patients with 6-mm ablation zones with refractive errors from -2.88 to -9.25 D found that patients with large mesopic pupils did have more quality of vision issues at one month, but not at six months. Of the 100 eyes studied, only two were measured as greater than 7 mm under mesopic conditions, no doubt an underestimate of the true number of patients with scotopic pupils larger than 7 mm. Why do I say this? The pupils were measured under low light (<5 lux) with the Colvard device.
An article by Netto defines scotopic measurements using the Procyon pupillometer as being performed at 0.04 lux and mesopic high at 4 lux.2 That group studied 192 eyes and found that the mean scotopic pupil size was about 6.5 mm; the mean low mesopic pupil size was about 5.6 mm; and the mean high mesopic was about 4.0 mm. A study by Twa compared infrared video and digital photography to the Colvard at three different lux settings.3 On average the infrared or digital measurements at <0.63 lux (scotopic) were about 0.5-mm larger than the measurements with the Colvard at about 5 lux. Because of the testing method, the Schallhorn study most likely underestimated true scotopic pupil size. If just one or two patients with ?small pupils? who had NVC actually had scotopic pupils greater than 6.5 mm, the analysis and conclusions would have been different. The correlation with NVC and large pupils present at one month may have also been present at six months. Since one-third of these 100 patients missed their last follow-up visit, it is uncertain whether the conclusion that the correlation with pupil size present at one month was not still true at six months. The fact that many patients with NVC complaints and large pupils ?cortically adapt? to their new vision doesn?t mean the pupils were not a factor in their original complaints.
|Author:||Bill [ Wed Oct 24, 2007 2:57 pm ]|
Schallhorn debunked by Lone Dog:
http://www.lasermyeye.org/keratoscoop/c ... c2003.html
|Author:||Bill [ Sun Oct 28, 2007 7:40 pm ]|
Curr Opin Ophthalmol. 2006 Aug;17(4):373-9.
Pupil size and corneal laser surgery.
Salz JJ, Trattler W.
University of Southern California and Los Angeles County Medical Center, Los Angeles, California 90048, USA. firstname.lastname@example.org
In 2003 a study by Schallhorn et al.  on 100 eyes found that patients with large mesopic pupils had more quality-of-vision issues at 1 month but not at 6 months.
Our first concern about this study is that the pupils were measured under low light (<5 lux) with the Colvard pupillometer (Oasis Medical, Glendora, California). Netto et al.  define scotopic measurements using the Procyon pupillometer (Keeler USA, Broomall, Pennsylvania) as being performed at 0.04 lux and mesopic high at 4 lux. They studied 192 eyes and found that the mean scotopic pupil size was about 6.5mm whereas the mean low mesopic pupil size was about 5.6mm and the mean high mesopic was about 4.0mm. Twa et al.  found that infrared or digital measurements at less than 0.63 lux (scotopic) were about _0.5mm larger than the measurements with the Colvard at about 5 lux. Owing to the testing method, the Schallhorn et al. study underestimated true scotopic pupil size. Of the 100 eyes studied, only two were measured as greater than 7 mm. Thus if only a few of the patients with pupils measured as less than 6mmwho had NVCs had had scotopic pupils greater than 7mm, the analysis and conclusions would have been different. A second concern is that the conclusions are based on a subjective questionnaire and many patients adjust to these night vision problems (?cortical adaptation?) even though they are still aware of them. The final concern is lack of follow-up; a third of the patients missed the last visit.
|Author:||Fed Up Doc [ Mon Jan 07, 2008 10:10 pm ]|
This study can be easily nuked by just one of three major flaws.
1) Methology of pupil measurement. If Dr. Schallhorn didn't control the lighting and duration of dark-adaptation, the pupil measurements are wrong. Actually, the average pupil size in the study is too small for the average patient age. If you can prove that the pupil sizes were undermeasured, you can discredit the entire study.
2) Range of myopia, low to high. Even Dr. Schallhorn would likely not disagree that high myopia increases the risk for night vision disturbances. Patients with low refractive error have greater effective optical zones, everything else being equal.
3) Optical zones varied from 6.0 to 6.0 x 4.5 mm. The most obvious problem with this study is the varying optical zone diameters. Nearly half of the eyes in this study had an elliptical ablation to treat astigmatism. The optical zone of the minor axis was as small as 4.5 in some patients. You simply cannot compare a 6.0 spherical OZ with a 6.0 x 4.5 elliptical OZ.
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