Science: Intraocular Pressure and Optic Nerve Head Morphology during Scleral Lens Wear
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david 3.9k
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Source: Walker MK, et al. Optom Vis Sci. 2020;doi:10.1097/OPX.0000000000001567 April 20, 2021

TL:DR

This study has limitations that make it of little value for glaucoma patients.

Abstract

SIGNIFICANCE 

Scleral lenses (SLs) are increasing in scope, and understanding their ocular health impact is imperative. The unique fit of an SL raises concern that the landing zone causes compression of conjunctival tissue that can lead to resistance of aqueous humor outflow and increased intraocular pressure (IOP).

PURPOSE 

This study aimed to assess changes in optic nerve head morphology as an indirect assessment of IOP and evaluate other IOP assessment methods during SL wear.

METHODS 

Twenty-six healthy adults wore SL on one randomly selected eye for 6 hours, whereas the fellow eye served as a control. Global minimum rim width (optical coherence tomography) and IOP (Icare, Diaton) were measured at baseline, 2 and 6 hours after SL application, and again after SL removal. Central corneal thickness, anterior chamber depth, and fluid reservoir depth were monitored.

RESULTS 

Minimum rim width thinning was observed in the test (−8 μm; 95% confidence interval [CI], −11 to −6 μm) and control (−6 μm; 95% CI, −9 to −3 μm) eyes after 6 hours of SL wear (P < .01), although the magnitude of thinning was not significantly greater in the lens-wearing eyes (P = .09). Mean IOP (Icare) significantly increased +2 mmHg (95% CI, +1 to +3 mmHg) in the test eyes (P = .002), with no change in the control eyes. Mean IOP changes with Diaton were +0.3 mmHg (95% CI, −0.9 to +3.2 mmHg) in the test eyes and +0.4 mmHg (95% CI, −0.8 to +1.7 mmHg) in the control eyes. However, Diaton tonometry showed poor within-subject variation and poor correlation with Icare. No clinically significant changes were observed in central corneal thickness or anterior chamber depth.

CONCLUSIONS 

This study suggests that SLs have a minimal effect on IOP homeostasis in the normal eye during SL wear and an insignificant impact on the optic nerve head morphology in healthy adult eyes. However, the long-term effects of scleral lenses on IOP and optic nerve head structure, especially in susceptible eyes, should be investigated.

FitEyes commentary: The abstact doesn't include the following statement from the full text:

After removal of the scleral lenses, the Icare IOP was significantly greater in the test eyes than in the control eyes. This is in relative agreement with the study by Aitsebaomo et al., which also used Icare, although they saw an average increase about three times greater.

The remaining questions are whether the increased Icare measurements are true, and if so, are they caused by prolonged IOP increase during scleral lens wear or caused by the process of lens removal itself?

This study has several limitations.

It was short term and in normal subjects; long-term studies in diseased eyes may show different results, and this type of study should be repeated in individuals with glaucoma and keratoconus specifically. In addition, the duration of IOP increase measured with Icare after lens removal was not determined, and future studies should measure IOP for several minutes or longer after lens removal.

IOP was measured using two different methods. One of those was a very unreliable tonometer (Diaton). The authors state, "Ultimately, Diaton cannot be considered an accurate and reliable instrument for IOP assessment during scleral lens wear." In my opinion, they should have known that before they started and the Diaton should not have been used for any research that requires accuracy. (It might be a suitable screen tool in special circumstances, but it is not useful for much more.)

IOP and Optic Nerve Head Morphology during Scleral Lens Wear : Optometry and Vision Science

ResearchGate link: https://www.researchgate.net/publication/344277572_IOP_and_Optic_Nerve_Head_Morphology_during_Scleral_Lens_Wear

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