Clinical applications of wavefront refraction.

PURPOSE: To determine normative reference ranges for higher-order wavefront error (HO-WFE), compare these values with those in common ocular pathologies, and evaluate treatments. METHODS: A review of 17 major studies on HO-WFE was made, involving data for a total of 31,605 subjects. The upper limit of the 95% confidence interval (CI) for HO-WFE was calculated from the most comprehensive of these studies using normal healthy patients aged 20 to 80 years. There were no studies identified using the natural pupil size for subjects, and for this reason, the HO-WFE was tabulated for pupil diameters of 3 to 7 mm. Effects of keratoconus, pterygium, cataract, and dry eye on HO-WFE were reviewed and treatment efficacy was considered. RESULTS: The calculated upper limit of the 95% CI for HO-WFE in a healthy normal 35-year-old patient with a mesopic pupil diameter of 6 mm would be 0.471 µm (471 nm) root-mean-square or less. Although the normal HO-WFE increases with age for a given pupil size, it is not yet completely clear how the concurrent influence of age-related pupillary miosis affects these findings. Abnormal ocular conditions such as keratoconus can induce a large HO-WFE, often in excess of 3.0 µm, particularly attributed to coma. For pterygium or cortical cataract, a combination of coma and trefoil was more commonly induced. Nuclear cataract can induce a negative spherical HO-WFE, usually in excess of 1.0 µm. CONCLUSIONS: The upper limit of the 95% CI for HO-WFE root-mean-square is about 0.5 µm with normal physiological pupil sizes. With ocular pathologies, HO-WFE can be in excess of 1.0 µm, although many devices and therapeutic and surgical treatments are reported to be highly effective at minimizing HO-WFE. More accurate normative reference ranges for HO-WFE will require future studies using the subjects' natural pupil size.

Acute red eye (non-ulcerative keratitis) associated with mini-scleral contact lens wear for keratoconus.

Mini-scleral lenses are an increasingly popular contact lens modality; however, there are relatively few reports regarding the unique aspects of their fitting and potential complications. We report a complication of mini-scleral lens wear in a 44-year-old female patient using the lenses for keratoconus. Her mini-scleral contact lenses were non-fenestrated and fitted to vault over the cornea and seal at the periphery. The patient presented with an acute red eye (non-ulcerative keratitis), characterised by unilateral severe conjunctival and limbal hyperaemia, corneal infiltration and pain. Refitting the lens to increase the corneal vault clearance did not prevent recurrence of the keratitis, some five months later. Successful prevention of further episodes of the acute red eye was achieved through improved patient compliance with lens cleaning, disinfection and lens case procedures. Lens hygiene may be particularly important for mini-scleral lenses with a sealed fitting.

Prelens tear stability: relationship to symptoms of dryness.

BACKGROUND: Prelens tear thinning time (PLTTT) was used to quantify tear stability relative to symptoms of dryness. METHODS: Twenty-two subjects were measured for PLTTT in this investigator-masked study. Specular reflection was performed, and the timed appearance of a colored interference fringe within the reflection under high magnification indicated PLTTT. Two symptom questionnaires were given: subjective evaluation of symptom of dryness (SESoD) and Ocular Surface Disease Index (OSDI). RESULTS: The median PLTTT was 3.9 seconds for asymptomatic lens wearers. For those with dryness, the median PLTTT was 2.2 seconds. For SESoD, 69% of asymptomatic subjects had an average PLTTT of 3.0 seconds or greater. Eighty-three percent of symptomatic subjects had an average PLTTT of less than 3.0 seconds (P = 0.03). For OSDI, 71% of asymptomatic subjects had an average PLTTT of 3.0 seconds or greater. Seventy-five percent of symptomatic subjects had an average PLTTT of <3.0 seconds (P = 0.04). CONCLUSIONS: The data suggest that a PLTTT breakup time of <3.0 seconds might be suitable criterion for tear film dysfunction causing dryness symptoms. PLTTT may be a rapid and useful clinical method for practitioners to provide a glimpse of self-reported symptoms caused by contact lens-related dryness.

A review of the Holden-Mertz criteria for critical oxygen transmission.

PURPOSE: Holden and Mertz established the foundations for the new generation of silicone hydrogel contact lenses for daily and extended wear in 1984. Absence of lens-induced corneal swelling was their premise and although this was possible with daily wear, the goal with extended wear seemed almost impossible because of the limitation of hydrogel materials. Experience with extended and daily wear of disposable contact lenses during the last 2 decades and, more recently, with silicone hydrogels has led to the reconsideration of the validity of the findings of Holden and Mertz. RESULTS: A pivotal influence on the Holden and Mertz critical Dk/t value for closed-eye lens wear was exerted by two numbers: the no-lens wear corneal edema level (4%) and the silicone lens data point (Dk/t of 182x10, closed-eye edema level of 2.6%). Subsequent publications appear to give a more accurate assessment of the no-lens closed-eye corneal edema level, and there are also more recent measurements of silicone hydrogel lens Dk/t and corneal edema responses. CONCLUSIONS: It now appears that the Holden and Mertz criteria for extended-wear critical Dk/t should be revised upwards to at least 125x10.