Tear Film and Lid Margins in Over-Blink

Abstract

 

Purpose

 

It is generally accepted that the eyelid margins touch each other in spontaneous blinks while spreading the lipid over the tear film in the upwards movement of the upper lid. In contrast, recent research has demonstrated that the central upper lid (UL) and lower lid (LL) do not touch in spontaneous blinks due to an over-blink (OB). Furthermore a lissamine green drop, placed onto the anterior portion of the central LL, was demonstrated to be unchanged in spontaneous blinks (drop-test). The aim of this project was to evaluate UL and LL margins movements and a possible tear film spreading model based on the new knowledge.

 

Methods

 

In 15 subjects (9 female; median age= 45) lid-margin thickness of the opened eye was measured by Pentacam. Drop-test was performed over a period of 60sec. Blinks were filmed by high-speed video from a temporal-inferior view to analyse OB (Fig. 1) and LL margin movement (z-axis). UL tear meniscus depth (UL-TMD; horizontal width between UL margin and cornea; z-axis) was observed in the opened eye and almost closed eye via a mirror and slit lamp microscope. Image J Software was used for digital analysis of TMD and LL movement. OB was simulated in vitro by a dynamic blink model (glass-plates (=lids and cornea; saline solution = tear film (TF)).

 

Results

 

In-vivo: median lid margin thickness was 1.8mm (LL) and 1.9mm (UL), but not significant different (p=0.258). Lissamine green drops stayed unaltered in all subjects. Median OB grade was 3. The LL margin tightened in blinks by 1.2mm (median) but this was not related to OB (r=-0.25; p=0.220). Median TMD ratio (TMD almost closed eye / TMD opened eye) was 1.8 indicating an increasing separation of the upper eyelid margin from the cornea. This small effect was significantly correlated to OB (r=0.875; p<0.001). TM appeared to retreat slightly behind the UL (in y-axis direction, toward the cul-de-sac). In-vitro: When dynamically simulating OB the in-vitro TMD increased and the in-vitro TM retreated. TF was anchored to the UL by surface tension and mixed with the LL TM even without lid contact.

 

Conclusions

 

Central keratinized lid margins frequently do not touch in spontaneous blinks and it appears that the central keratinized lid margins are not aligned, as is traditionally presumed. This appears not to impact tear film spreading.

 

 

Figure 1: Grading scale of over-blink

 

Keywords: 526 eyelid • 486 cornea: tears/tear film/dry eye • 421 anterior segment