Abstract
Background: In 1508 Leonardo Da Vinci illustrated a man with his head in a bowl of water; this was interpreted as the beginning of corneal neutralisation and one could argue, led eventually to the concept of contact lenses. Since then, rapidly evolving technology has led to the rebirth of scleral lens (SL) fitting in recent years. A SL is a gas permeable contact lens (CL) that vaults the cornea and rests on the sclera, therefore, the weight of the lens is distributed across the landing area on the sclera. The vault of the SL creates a tear reservoir between the lens and the cornea which is partially responsible for the improvement in visual acuity for SL wearers. The use of SLs is becoming more common and diversified. The indications and applications of these lenses range from treating refractive errors to the management of corneal diseases.
It has been postulated that this form of optical device may lead to the disruption of aqueous humour outflow. This disruption may lead to an increase in intraocular pressure (IOP). Studies have attempted to explain reasons as to why SL wear might influence IOP. Furthermore the vaulting of the cornea by the SL creates a barrier to oxygen supply from the atmosphere. A reduction in oxygen supply creates hypoxic conditions that encourage oedema which leads to an increase in corneal thickness (CT).
Purpose: The aim of this study was to investigate the effect of small diameter scleral lenses on IOP and central corneal thickness (CCT) of healthy young individuals and evaluate SL settling.
Method: Twenty nine (29) participants, between the ages of 18 35 years, were fitted with small diameter (≤ 16 mm) SL on their right eyes. Intra ocular pressure and CCT were measured before and after four hours of SL wear. The instruments used to measure the variables of interest were an iCare rebound tonometer (Helsinki, Finland) and an Oculus Pentacam (Oculus GmbH, Germany) and scleral lens settling was also measured with the iVue SD OCT (Optovue Inc., CA).
Results: This dissertation presents the findings of a study to observe the effects of a small diameter scleral lens on IOP and CCT in young adults. The evaluation of the two variables (IOP and CCT) will help provide a greater understanding of how SLs affect the eye during lens wear. Although this study involved healthy participants, it may guide our management of patients with pre existing conditions such as glaucoma or corneal diseases such as keratoconus that need to be fitted with these specialty lenses. For each participant, their right eye was fitted with a SL and their left eye was used as a control. The study found no statistically significant difference in IOP and CCT after four hours of SL use. There was, however, a slight elevation with IOP and CCT. Scleral lenses were found to have settled after the four hours of SL wear.
Conclusion: This study displayed a slight increase in IOP and CCT, but the differences were not significant. Scleral lens settling was found to have taken place, after the four hours of SL. These findings suggest that SLs should be assessed after longer wearing periods so as to further understand the possible effects of SL in healthy and other eyes.