Accurate pupillometry is an essential part of the evaluation for refractive surgery. With reports of halos and glare following refractive surgery on many of the prime-time news shows, pupillometry has become one of the preoperative tests that patients expect. It is very clear from the published and anecdotal reports of nighttime glare and halos that a large pupil is the predominant factor leading to these problems.

The need to detect the patients with large pupils as a part of the refractive evaluation makes precise pupillometry measurements crucial. I’ve been involved in a malpractice suit in which the pupils were estimated to be 6 mm (using a Rosenbaum Chart with pupil sizes at the bottom). When accurate

The Colvard device uses infrared light that does not affect the pupil size.

pupillometry was done, they were found to be 7.5 mm. The patient, a commercial pilot with 20/20 postop daytime vision in both eyes, is no longer able to fly because of disabling nighttime glare. His estimated loss of future income, as well as a loss in his quality of life has resulted in a claim of more than $5 million. I have seen the patient and the surgery was done perfectly.

In this article, I’ll review the tools available to refractive surgeons. I have used all of these instruments and will list the features and accuracy of each.

Effective vs. Intended OZ
The normal pupil size varies with age and gender. The pupil gets smaller with age and men usually have smaller pupils than women of the same age. In studies in which I’ve participated of patients seeking refractive surgery, the average patient is 42 years of age and the average pupil diameter is approximately 6 mm, with a standard deviation of approximately ± 1.0 mm. These values would indicate that 67 percent of our refractive patients have between 5 and 7 mm pupils. These values also indicate that 17 percent of the patients have pupils larger than 7 mm and approximately 2.5 percent have greater than an 8-mm pupil.

Surgeons should also consider that the “effective optical zone” size is always smaller than the “intended” optical zone size stated by the manufacturer. Studies have demonstrated that the effective optical zone for almost every

	The Procyon system calculates the average size of 10 pupil images captured in 2 seconds.

commercial laser is 10 percent smaller than intended for a – 5 D treatment, 23 percent smaller for a   – 10 D treatment, 37 percent smaller for a – 15 D treatment and 52 percent smaller for a –  20 D treatment.

For an intended 6.5 mm treatment, the actual effective optical zone size with existing lasers is 5.9, 5.0, 4.1 and 3.1 mm for the – 5, –10, –15 and – 20 D treatment, respectively. To avoid any glare from pupil and effective optical zone disparity, the effective optical zone size should be the same size as the scotopic pupil size and perfectly centered with the pupil. An additional 1- or 2-mm blend zone beyond the effective optical zone is needed to avoid a sharp transition from the treated to untreated area that can cause unwanted images in the peripheral vision.

Requiring the effective optical zone size to be equal to the scotopic pupil is the strictest possible criterion, but it is the safest approach today. It may be possible to make the effective optical zone size slightly smaller than the scotopic pupil size due to the Stiles-Crawford effect and the ability of some patients to tolerate mild halos and glare at night. Nevertheless, it is prudent today not to go significantly beyond this limit. I have patients treated in years past who are far below this limit and most of them are very happy. However, our understanding of the night vision problems and the standard of care have increased, so I would be much less likely to treat many of these patients today with a standard excimer laser.

Pupillometry Options
The are three basic types of commercial pupillometers on the market (not for laboratory, but for routine clinic use):
 
• objective infrared video camera with pupil detecting system;

 • infrared tubes with a reticule or display; and

 • gauges.

The only commercial infrared video camera system is the Procyon P2000SA binocular pupillometer, distributed in the United States by Keeler. The system calculates the average size of 10 pupil images captured in 2 seconds. It can measure at three user-adjustable light levels (scotopic, low mesopic and high mesopic) and prints a graph or table. A target at optical infinity reduces the

The Pupilscan II (top) displays the pupil image and a digital readout of the pupil size to ± 0.1 mm. The use of cards and gauges, such as the Holladay Pupil Gauge, relies more on a trained, skilled technician, but can be effective.

effect of accommodation on pupil size (similar to an autorefractor). The instrument is accurate to ± 0.1 mm, which is greater than the physiological variability in the pupil size. The test takes less than 5 minutes to perform, and it may be moved from one examination room to another, but is usually placed at one station.

The two instruments with infrared tubes are the Colvard Pupillometer,  manufactured by Oasis Medical, and the Pupilscan II Model 12A, distributed by Keeler. The Colvard device allows the observer to see the pupil using infrared light that does not affect the pupil size and a graduated reticule that overlays the pupil. Each examiner must adjust the eyepiece so that the reticule is in clear focus at the time of the measurement for the reading to be accurate. After technician training, the clinical measurement is accurate to approximately ± 0.5 mm (reticule tolerance is to ± 0.1 mm).

The Pupilscan II displays the pupil image and a digital readout of the pupil size to ± 0.1 mm. For both instruments, accommodation is overcome by having the patient look at a distant object during the pupil measurement in a dark room.
There are a number of pupil gauges on the market and near vision cards with half or full pupils for matching the pupil size (Some, such as the Rosenbaum Card, are free from many ophthalmic or pharmaceutical companies). The ability of a technician to match the size of a pupil to a black hemi-circle or circle is very good with good illumination and
practice.

The major problem measuring the scotopic pupil is lighting. In the past, we have recommended using a cobalt blue light (penlight with a cobalt blue filter) and holding it on the temporal side to minimize the effect of pupillary constriction from the light.

With practice, this technique works well in blue eyes, but in dark brown eyes it is quite difficult to be sure of the size without some direct light on the iris. Some direct light inevitably projects through the pupil and may cause some pupil constriction. Accommodation is overcome by having the patient look at a distant object such as the distance eye chart. With practice and a very conscientious observer, this technique is accurate to ± 1.0 mm in brown eyes and sometimes a little better in blue eyes.

As I stated at the outset, an accurate scotopic pupil measurement as a part of the preoperative evaluation is just as important as accurately measuring the refraction and the thickness of the cornea. Whichever technique you choose, the information should be documented in the chart and the test repeated if there is any question on the part of the technician as to the exact pupil size. An accurate pupil measurement and predicting the effective optical zone size for an intended treatment is the best way to avoid disabling nighttime glare and halos and to avoid any malpractice suits based on the current standard of care for refractive surgery. 

Dr. Holladay is the developer of the Holladay Pupil Gauge from ASICO. He is in private practice and is a clinical professor of ophthalmology at Baylor College of Medicine. Contact him  at (713) 668- 7337, fax (713) 668-7336 or docholladay@docholladay.com.

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2. Holladay JT, Moran JR, Kezirian GM. Analysis of aggregate surgically induced refractive change, prediction error, and intraocular astigmatism. J Cataract Refract Surg 2001;27:61-79.
3. Hugger P, Kohnen T, La Rosa FA, Holladay JT, Koch DD. Comparison of changes in manifest refraction and corneal power following photorefractive keratectomy. Am J Ophthalmol 2000; 129:68-75.
4. Budak K, Khater TT, Friedman NJ, Holladay JT, Koch DD. Evaluation of relationships among refractive and topographic parameters. J Cataract Refract Surg 1999;25:814-20.
5. Holladay JT, Dudeja DR, Chang J. Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography. J Cataract Refract Surg 1999;25:663-69.
6. Holladay JT. Corneal topography using the Holladay Diagnostic Summary. J Cataract Refract Surg 1997;23:209-21.
7. Hersh PS, Shah SI, Geiger D, Holladay JT. Corneal optical irregularity after excimer laser photorefractive keratectomy. The Summit Photorefractive Keratectomy Topography Study Group. J Cataract Refract Surg 1996;22:197-204.
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9. Holladay JT, Lynn MJ, Waring GO, Gemmill M, Keehn GC, Fielding B. The relationship of visual acuity, refractive error, and pupil size after radial keratotomy. Arch Ophthalmol 1991;109:70-76.

Resources

Procyon P2000SA U.S. Distributor: Keeler Inc. 1 (800) 523-5620, (610) 353-4350, fax: (610) 353-7814 Cost: $11,950 (excluding cost of laptop computer) keeler@keelerusa.com www.keelerusa.com

Colvard Pupillometer Oasis Medical 1(800) 528-9786 (626) 914 2891, fax: (636) 914-2285 Cost: $1,600

Pupilscan II Model 12A Keeler Inc., as above Cost: $1,795

Holladay Pupil Gauge ASICO 1 (800) 628-2879, fax: (630) 986 0065 Cost: $35 per gauge