Journal of Refractive Surgery

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Letters to the Editor 

Mystery of the Clonic Orbscans

Julio Ortega-Usobiaga, MD, PhD; Clara Martín-Reyes, MD; Victoria De Rojas, MD, PhD; Fernando Llovet, MD, PhD; Jaime Beltrán, MD; Julio Baviera, MD

Abstract

The Orbscan II (Bausch & Lomb, Rochester, NY) system of ocular topography is a synergy of two corneal videokeratography techniques: a Placido-disk attachment (front surface curvature data) and a slit-scanning technology (elevation topography: anterior and posterior surfaces of the cornea and anterior surface of the lens).1–4 Three cases are presented in which the Orbscan device failed to map the corneal surfaces.

A 71-year-old woman underwent an ocular examination that revealed no pathology, except for shallow anterior chambers and narrow angles, and bilateral mild senile cataracts. Orbscan II was performed (Fig 1A) and the anterior elevation best fit sphere map was repeated in the four quadrants (clonic quad map, with the four maps all the same) instead of displaying the “usual” quad map (with four different maps). The test was then repeated in the same as well as a different Orbscan device with identical results. The program was able to display keratometric tangential and axial power maps, as well as the Placido image of the eye (Fig 1B) separately, but no other maps could be obtained. Moreover, the device was not able to detect the anterior chamber depth, corneal thickness, or kappa angle.

Laser YAG iridotomy was performed in both eyes and 30 minutes later Orbscan II was repeated. The “usual” quad map (pre-selected by the software) was displayed and the clonic quad map disappeared (see Fig 1B). The anterior chamber depth (ultrasound biometry) was 2.41 mm and 2.30 mm for the right and left eyes, respectively.

Two women, aged 52 and 39 years, respectively, presented without any ocular pathology except for shallow anterior chambers. When Orbscan II was per-formed, the anterior elevation best fit sphere map was repeated in the four quadrants (clonic quad map) instead of displaying the “usual” quad map. A laser YAG iridotomy was performed bilaterally and the Orbscan II was repeated, showing a “usual” quad map.

All eyes showed normal ophthalmic examination except shallow anterior chambers. On performing the Orbscan topography, the device could only obtain data from the anterior corneal surface and displayed the anterior best fit sphere elevation map. Failing to reproduce the quad map, the device repeated the only map obtained from the anterior surface and a clonic quad map was produced. The software was able to obtain the keratometric tangential and axial maps (data from Placido-disk exclusively), but not the keratometric total map (data from the hybrid Placido/slit lamp). A computer error can be ruled out, as the “clonic” maps were obtained in different Orbscan II devices, and Bausch & Lomb technicians checked the Orbscan II systems, and did not find anything amiss.

Pérez Silguero et al5 reported a case similar to our third case: a middle-aged female patient with a shallow anterior chamber and a “clonic” quad map image. After laser YAG iridotomy was performed, Orbscan II showed the “usual” quad map.

Julio Ortega-Usobiaga, MD, PhD
Clara Martín-Reyes, MD
Victoria De Rojas, MD, PhD
Fernando Llovet, MD, PhD
Jaime Beltrán, MD
Julio Baviera, MD
Bilbao, Spain

To the Editor:

The Orbscan II (Bausch & Lomb, Rochester, NY) system of ocular topography is a synergy of two corneal videokeratography techniques: a Placido-disk attachment (front surface curvature data) and a slit-scanning technology (elevation topography: anterior and posterior surfaces of the cornea and anterior surface of the lens).1–4 Three cases are presented in which the Orbscan device failed to map the corneal surfaces.

A 71-year-old woman underwent an ocular examination that revealed no pathology, except for shallow anterior chambers and narrow angles, and bilateral mild senile cataracts. Orbscan II was performed (Fig 1A) and the anterior elevation best fit sphere map was repeated in the four quadrants (clonic quad map, with the four maps all the same) instead of displaying the “usual” quad map (with four different maps). The test was then repeated in the same as well as a different Orbscan device with identical results. The program was able to display keratometric tangential and axial power maps, as well as the Placido image of the eye (Fig 1B) separately, but no other maps could be obtained. Moreover, the device was not able to detect the anterior chamber depth, corneal thickness, or kappa angle.

Clonic Quad Map, with the Anterior Elevation Best Fit Sphere Map Repeated in the Four Quadrants.

Figure 1A. Clonic Quad Map, with the Anterior Elevation Best Fit Sphere Map Repeated in the Four Quadrants.

“Usual” Quad Map, After Laser YAG Iridotomy.

Figure 1B. “Usual” Quad Map, After Laser YAG Iridotomy.

Laser YAG iridotomy was performed in both eyes and 30 minutes later Orbscan II was repeated. The “usual” quad map (pre-selected by the software) was displayed and the clonic quad map disappeared (see Fig 1B). The anterior chamber depth (ultrasound biometry) was 2.41 mm and 2.30 mm for the right and left eyes, respectively.

Two women, aged 52 and 39 years, respectively, presented without any ocular pathology except for shallow anterior chambers. When Orbscan II was per-formed, the anterior elevation best fit sphere map was repeated in the four quadrants (clonic quad map) instead of displaying the “usual” quad map. A laser YAG iridotomy was performed bilaterally and the Orbscan II was repeated, showing a “usual” quad map.

All eyes showed normal ophthalmic examination except shallow anterior chambers. On performing the Orbscan topography, the device could only obtain data from the anterior corneal surface and displayed the anterior best fit sphere elevation map. Failing to reproduce the quad map, the device repeated the only map obtained from the anterior surface and a clonic quad map was produced. The software was able to obtain the keratometric tangential and axial maps (data from Placido-disk exclusively), but not the keratometric total map (data from the hybrid Placido/slit lamp). A computer error can be ruled out, as the “clonic” maps were obtained in different Orbscan II devices, and Bausch & Lomb technicians checked the Orbscan II systems, and did not find anything amiss.

Pérez Silguero et al5 reported a case similar to our third case: a middle-aged female patient with a shallow anterior chamber and a “clonic” quad map image. After laser YAG iridotomy was performed, Orbscan II showed the “usual” quad map.

Julio Ortega-Usobiaga, MD, PhD
Clara Martín-Reyes, MD
Victoria De Rojas, MD, PhD
Fernando Llovet, MD, PhD
Jaime Beltrán, MD
Julio Baviera, MD
Bilbao, Spain

References

  1. Cairns G, McGhee CN. Orbscan computerized topography: attributes, applications, and limitations. J Cataract Refract Surg. 2005;31:205–220. doi:10.1016/j.jcrs.2004.09.047 [CrossRef]
  2. Cairns G, McGhee CN, Collins MJ, Owens H, Gamble GD. Accuracy of Orbscan II slit-scanning elevation topography. J Cataract Refract Surg. 2002;28:2181–2187. doi:10.1016/S0886-3350(02)01504-3 [CrossRef]
  3. Lim KL, Fam HB. Relationship between the corneal surface and the anterior segment of the cornea: an Asian perspective. J Cataract Refract Surg. 2006;32:1814–1819. doi:10.1016/j.jcrs.2006.08.022 [CrossRef]
  4. Maldonado MJ, Nieto JC, Diez-Cuenca M, Piñero DP. Repeatability and reproducibility of posterior corneal curvature measurements by combined scanning-slit and placido-disc topography after LASIK. Ophthalmology. 2006;113:1918–1926. doi:10.1016/j.ophtha.2006.05.053 [CrossRef]
  5. Pérez Silguero D, Merlo Romero J, Jiménez García MaA, Pérez Silguero MA. Evaluación y comparación del grosor corneal en ojos patológicos utilizando ultrasonidos y el sistema topográfico Orbscan. Studium Ophthalmologicum. 2006;XXIV:n°4.

10.3928/1081597X-20090917-03

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