**1. Introduction**

Dry eye (DE) is a multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film and accompanied by ocular symptoms [1]. The prevalence of DE has increased considerably worldwide over the last three decades [2]. Some patients with DE experience severe pain that reduces their quality of life (QoL) with minimal ocular surface signs [1,3]. Their manifestations include a variety of unpleasant spontaneous ocular sensations, such as burning, aching, and photoallodynia [1,3]. A neurobiological mechanism is known to underline the ocular symptoms of DE [3].

The classification of pain is based on the underlying etiology: nociceptive, neuropathic, and mixed [4]. The primary approach to treating severe ocular pain is to target potential nociceptive factors [5]. Topical treatment could be attempted to lower tear osmolarity and reduce inflammation [6]. If the pain cannot be resolved with the primary approach, neuropathic pain could be considered [5,7,8]. In DE, persistent damage to the ocular surface and nerve endings induced by tear film instability and inflammation can cause peripheral neuronal sensitization. Moreover, repeated peripheral nerve injury can lead to central neuronal sensitization [9–12].

DE and neuropathic pain share several common features, including frequent discordance between the symptoms and signs, abnormal somatosensory testing, accompanying comorbidity, and anatomic nerve injury or somatosensory nerve sensitization [9,13]. Ocular pain symptoms disproportionally outweighing the clinical signs are suggestive of an underlying neuropathic etiology that requires systemic pain managemen<sup>t</sup> [9,13].

Oral gabapentin is the first-line agen<sup>t</sup> for the treatment of chronic systemic neuropathic pain [14]. Especially, gabapentin could reverse elements of central sensitization in patients with chronic pain [15–17]. This agen<sup>t</sup> has been studied as a therapy for ocular pain after refractive surgery and painful DE [7,18–20]. However, central nervous system (CNS) depression may occur as a side effect [15], and the therapeutic efficacy of gabapentin for neuropathic ocular pain (NOP) has not been verified. Hence, ophthalmologists are less likely to use gabapentin for treating NOP which is refractory to topical agents. In this study, we aimed to investigate the response to gabapentin treatment in DE patients with NOP features and compare the clinical parameters and ocular pain assessment survey (OPAS) scores between groups according to the treatment response.
