1. NAKED-EYE MATCHES
   Divers with in-air Rx of – 4.00 to -5.00, no acute presbyopia and cylinder less than 1.0 can use the mask with their naked eyes.

   ---

2. ACCOMMODATORS
   Divers with in-air Rx of – 2.50 to -3.75 and cylinder less than 1.0 can use the mask with their naked eyes if they have good accommodation ability. Many early-20's emmetropes have used MEGA –4.5 prototypes with their naked eyes -- however to conservatively avoid eyestrain during lengthy (e.g. 60-minute) dark dives, we recommend not "over-prescribing" the mask more than 2.0 diopters of excess accommodation. For most up to their early-30's, a 1.5d excess neg-diopter state works very well. For late-30's / early-40's, match closer to the masks’ required net +4.50 eye power. Presbyopes may require mono-vision or modified mono-vision.
   
   Testing for accommodation AT HOME: The "125 mm / FIVE-Inch Test" can be performed at-home to confirm a diver can use the MEGA – 4.5 with their naked eyes. One must be able to sustain sharp focus on fingerprint-whorls comfortably at five inches for 60 seconds. That’s 8 diopters / 125 mm of accommodation while illuminated only by one candle at one foot from the finger.
   
   Testing for accommodation IN YOUR EXAM ROOM: Divers must be able to read their gauges in turbid water (12 inches in VERY dim light). Example: using the – 4.5 mask and focusing to 12 inches (–3.25D of accommodation) requires total accommodation of 7.25D. But the built-in "progressive effect" actually nets -6.5D accommodation required. Confirm the patient's 12-inch focus ability in dim light while they wear their new "diving" Rx contacts (or just myopic eyes) AND – 4.25 trial spectacle lenses over the CLs to simulate the mask’s effect.

   ---

3. DIVING Rx WEARERS (everybody else)
   Of course this is easiest for those with prior CL wear experience... just bring them within accommodation range.
   
   

1. EMMETROPES: induce the least amount of myopia for their surface-comfort. Most emmetropes are psychologically uneasy when temporarily myopic (i.e. for some, +3.0 may be OK but +4.50 may be too much). For younger divers, we suggest trying + 3.0 CLs, but be careful not to induce "temporary" hyperopia / presbyopia.
   
   
2. ADAPTING: Before heading out on a vacation on a rocking boat, divers with no CL experience – especially emmetropes – should first get comfortable with this new paradigm on DRY LAND. We suggest wearing Surface-Interval eyeglasses over Diving Rx CLs for a 2 hours a day x 3 days prior to a vacation departure.
   
   
3. CL BRAND CHOICE: Easy handling characteristics are important for divers who are new to CLs. While thin lenses are more comfortable, some may be better off with thicker lenses.
   

SURFACE-INTERVAL EYEGLASSES: For those who modify their vision with Diving Rx CLs, we offer low-cost eyeglasses in two styles for between-dive wear. Either style includes UV blocking polarized clilp-ons.
"Buddy Holly" style in -4.5 and -3.0 Rx.
"Harry Potter" style in any SV Rx; no edging required for these round lenses, since the bevel is molded in. What they lack in style they make up for in economy. Frames vary the PD (Narrow-Medium-Wide).