Measurements of contrast sensitivity and distortion aid surgical decision-making in eyes with macular pucker

Issue: August 10, 2016

Objective measures of contrast sensitivity and visual distortion can be used to assess the impact of macular pucker on visual function, according to a study.

“The study was designed to develop quantitative measures of vision in patients with macular pucker. Right now, we only have visual acuity, and that’s limited in its ability to really give us a handle on the degree of impact that macular pucker has on vision,” corresponding author J. Sebag, MD, FACS, FRCOphth, FARVO, told Ocular Surgery News.

Patients and methods

The prospective, comparative case series, published in Ophthalmology, included 41 patients with unilateral macular pucker and normal fellow eyes. By their own choice, 24 patients underwent pars plana vitrectomy with membrane peeling and 17 did not. A control group comprising 12 patients with visual distortions was used to test the reproducibility of distortion measurement.

“By measuring the contrast sensitivity and the degree of distortion, we were able to distinguish between these two groups. There were significant differences in people who had macular pucker that in their opinion was bad enough to have surgery compared with the group whose macular pucker was not so bad,” Sebag said.

Contrast sensitivity was measured with the Freiburg Visual Acuity Contrast Test, a Web-based test developed at the University of Freiburg in Germany. After at least 3 minutes of dark adaptation, the test is performed on standard backlit light-emitting diode display monitors, and the program automatically calculates contrast sensitivity measured as Weber index (%W). The higher the index, the lower the contrast sensitivity.

The three-dimensional threshold Amsler grid was used to quantify distortions (Figure 1). Development of the prototype system is primarily credited to Alfredo A. Sadun, MD, PhD, who holds a patent on the technology.

Among the 24 patients who had surgery, 13 eyes were phakic (54%) and 11 were pseudophakic (46%). Among control fellow eyes, 14 were phakic (58%) and 10 were pseudophakic (42%). Eyes with multifocal IOLs were excluded from the analysis.

Anatomic and visual outcomes

Average macular thickness in operated eyes decreased from 514 µm preoperatively to 390 µm at 1 month, 366 µm at 3 months, 357 µm at 6 months and 343 µm at 1 year (P < .001 for each interval). Final reduction of macular thickness was 33%. But at 12 months after surgery, macular thickness in operated eyes was still 34% greater than thickness in control fellow eyes (P < .001).

Figure 1. Three-dimensional threshold Amsler grid quantification of distortions in macular pucker. Patients are seated in front of a standard touch-screen computer monitor that displays an Amsler grid upon which they trace the area of distortion with a finger. The blue tracing in this figure represents the 2-D tracing at 100% contrast between the grid lines and the background. A total of five separate grids with varying contrast levels (20%, 40%, 60%, 80% and 100%) between the grid lines and the background are displayed, and the patient traces the area of distortion five times. These five grid tracings are stacked on the z-axis, and a volumetric plot (red lines) is created. The volume of this 3-D rendering quantifies the degree of distortion, expressed as percent volume lost relative to the hill of vision. This patient with macular pucker had 23.55% volume lost preoperatively. One month after vitrectomy/peel surgery without chromodissection, the distortions decreased to 5.09% volume lost, and at 12 months postop the distortions were nearly gone, at 1.7%. Overall, the 24 patients in this study averaged a 92% resolution of distortions after surgery.

“The interesting thing was that although the thickness of the central macula improved after surgery, it never became normal like the control fellow eyes,” Sebag said.

Mean macular volume, however, decreased from 3.22 µL preoperatively to 2.58 µL at 1 month, 2.44 µL at 3 months, 2.39 µL at 6 months and 2.29 µL at 1 year (P < .01). Macular volume was similar in operated eyes and control fellow eyes at 1 year.

“The volume of the macula not only improved but also became similar to the control fellow eyes, suggesting that measuring the volume of the macula could be more informative than just the thickness,” Sebag said.

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Posterior vitreous detachment was present in 23 of 24 eyes with macular pucker (96%) and in 12 of 24 control fellow eyes (50%); the between-group difference was statistically significant (P < .001).

Average logMAR visual acuity in operated eyes improved from 0.53 preoperatively to 0.38 at 1 month, 0.33 at 3 months, 0.35 at 6 months and 0.35 at 1 year (P < .001 for all time points).

Contrast sensitivity improved from 8.61 %W preoperatively to 5.36 %W at 1 month, 4.81 %W at 3 months, 5.26 %W at 6 months and 5.60 %W at 12 months; average improvement was 54% (P < .001).

Distortion index improved from 7.61 preoperatively to 2.46 at 1 month, 1.57 at 3 months, 0.62 at 6 months and 0.63 at 1 year (P < .001), representing a 92% resolution of distortions.

“We were able to show an improvement in the contrast sensitivity as well as an improvement in the quantitative index of distortions that was statistically significant at each time point, so it’s a very positive finding that helps us greatly,” Sebag said. – by Matt Hasson

References:
Gupta P, et al. Retina. 2008;doi:10.1097/IAE.0b013e318160a754.
Nguyen JH, et al. Ophthalmology. 2016;doi:10.1016/j.ophtha.2016.03.022.
Sebag J. The Vitreous – Structure, Function, and Pathobiology. New York: Springer-Verlag; 1989.
Sebag J, et al. Trans Am Ophthalmol Soc. 2007;105:121-129; discussion 129-131.
Sebag J. Vitreous – in Health & Disease. New York: Springer; 2014.

For more information:
J. Sebag, MD, FACS, FRCOphth, FARVO, can be reached at VMR Institute, 7677 Center Ave., Suite 400, Huntington Beach, CA 92647; email: jsebag@vmrinstitute.com.

Disclosure: Sebag reports no relevant financial disclosures.