Visual acuity and quality of life in dry eye disease: Proceedings of the OCEAN group meeting

Abstract

Dry eye disease (DED) results in tear film instability and hyperosmolarity, inflammation of the ocular surface and, ultimately, visual disturbance that can significantly impact a patient's quality of life. The effects on visual acuity result in difficulties with driving, reading and computer use and negatively impact psychological health. These effects also extend to the workplace, with a loss of productivity and quality of work causing substantial economic losses. The effects of DED and the impact on vision experienced by patients may not be given sufficient importance by ophthalmologists. Functional visual acuity (FVA) is a measure of visual acuity after sustained eye opening without blinking for at least 10 s and mimics the sustained visual acuity of daily life. Measuring dynamic FVA allows the detection of impaired visual function in patients with DED who may display normal conventional visual acuity. There are currently several tests and methods that can be used to measure dynamic visual function: the SSC-350 FVA measurement system, assessment of best-corrected visual acuity decay using the interblink visual acuity decay test, serial measurements of ocular and corneal higher order aberrations, and measurement of dynamic vision quality using the Optical Quality Analysis System. Although the equipment for these methods may be too large or unaffordable for use in clinical practice, FVA testing is an important assessment for DED.

Introduction

Dry eye disease (DED) is a multifactorial disease of the tears and ocular surface that results in visual disturbance and tear film instability, among other symptoms (Fig. 1). It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface [1], [2]. The tear film is the first part of the ocular surface that light meets on the pathway to the retina, and the large refractive index step from the air to the tears means that the precorneal tear film has the greatest dioptric power of any optical interface of the eye [3], [4]. Furthermore, the tear film compensates for the optical irregularity of the corneal epithelium surface, which is caused by the presence of numerous microvilli; without this compensation by the tear film, the quality of the transmitted light would be poor. As the retinal image depends upon light passing through the optical structures, the composition and homogeneity of the tear film may have a huge impact on the quality of the retinal image [5].

The tear film is inherently unstable and undergoes irregular disruptions following a blink, causing tear film break-up [4]. The resulting irregularity in the thickness of the tear film across the ocular surface will have a negative effect on the quality of this most important ocular dioptre, which normally has a refractive power of 48.35D [3], [4]. It has been well documented that in eyes with a short tear film break-up time (TFBUT), optical quality deteriorates significantly more quickly after the blink than it does in normal eyes [5], [6]. Patients with DED typically have a shorter TFBUT than normal controls [5], [7], and these patients show a reduction in visual acuity over time after holding the eye open for a few seconds [8]. As will be discussed later, an important impact of the short TFBUT in patients with DED is an increased blink rate [9]. The use of artificial tears in patients with DED has been shown to significantly improve visual acuity (mean acuity gain of +2.33 optotypes, which was considered to be highly significant in the study) and spatial contrast sensitivity, further supporting the importance of the role of the tear film in visual function [10], [11].

External factors that lead to DED include a low-humidity environment and contact lens use, while internal conditions may include, but are not limited to, Sjögren's syndrome, meibomian gland dysfunction (MGD), connective tissue disorders, Graves' disease, chronic graft-vs-host disease, pseudoexfoliation syndrome and skin diseases (e.g. ocular rosacea) [12], [13].

In this review, we examined the effects of DED on functional visual acuity (FVA) and their impact on the quality of life (QoL) of patients with DED.