Case report: Utilization of neutral density filters for densitometry analysis of dense corneal opacities

Abstract

Purpose: This report describes the technique of utilizing a neutral density filter (NDF) during Scheimpflug imaging of a dense corneal opacity in order to increase data acquisition success and improve data reliability for densitometry analysis.

Observations: A 49-year-old female with Steven-Johnson Syndrome secondary to sulfonamide use presented for routine follow up evaluation of her customized ocular surface prosthetic device (PD). Her ocular history was significant for mucous membrane grafting and limbal stem cell transplant in both eyes. The ocular surface examination of the left eye was notable for chronic dense neovascularization and scarring of the temporal and inferior cornea which extended into the visual axis. Scheimpflug imaging and densitometry analysis were performed in order to quantify the severity of the scar, however, there was significant difficulty in acquiring densitometry data. During a subsequent follow-up visit to monitor the scar, standardized room lighting and a neutral density filter were used to obtain reproducible and reliable imaging for densitometry analysis. The corneal scar was monitored over time using this standardized imaging protocol and by densitometry analysis minimal progression of the scar was evident, suggesting that recently documented significant vision loss in the left eye could not be attributed solely to changes in the scar.

Conclusion and importance: The use of a neutral density filter along with standardized ambient lighting conditions when performing Scheimpflug imaging may be necessary to reliably monitor densitometry progression of clinically severe corneal opacities.

Keywords: Corneal scar; Scheimpflug imaging; Scleral lens.

Fig. 1

A: Slit lamp biomicroscopy photograph of left eye taken at Visit 1. Fig. 1B: Slit lamp biomicroscopy photograph of left eye taken at Visit 3. (Images courtesy of BostonSight, Needham MA).

Fig. 2

One of the densitometry data maps acquired at Visit 1, left eye. Significant portions of the map reach the maximum allowable value of 100 (blue arrows). (Image courtesy of BostonSight, Needham MA). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3

A: Scheimpflug camera without 0.6 NDF, B Scheimpflug camera with 0.6 NDF in position (orange arrow), C: Scheimpflug image taken without NDF, D: Scheimpflug image taken with NDF. Note the reduction in reflectivity and proper posterior corneal surface registration with NDF in place. NDF: neutral density filter. (Image courtesy of BostonSight, Needham MA). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4

Average (full thickness cornea) densitometry readings. A: Visit 2, B: Visit 3, C: Change in average densitometry B-A, with a positive value signifying worsened opacification. Note the central black solid line circle in each image demarcates the central 3mm of the cornea.