NIGHT VISION IMPAIRMENT

Millions of LASIK surgeries have been performed in the United States in the past decade. Many patients now suffer from visual impairment at night. Some patients, especially those with large pupils, are unsafe to drive at night and can no longer live normal, independent lives.

Unfortunately the FDA turned a deaf ear on this recommendation and did not place a pupil size limit on the approval, nor did it include large pupils in the list of LASIK contraindications. Instead, the FDA approved lasers for LASIK with watered-down cautionary language in the labeling regarding large pupils. Dissemination of this labeling to patients was mandated by the FDA but not enforced, which violated the right to fully informed consent for many patients with large pupils.



Reduced visual quality in dim light is frequently reported by LASIK patients.1 Patients with pupils that dilate larger than the effective optical zone of the LASIK treatment are at increased risk for debilitating visual aberrations and loss of contrast sensitivity.5 Even patients with normal pupil sizes are at risk, as the laser loses efficiency on the slope of the cornea resulting in an effective optical zone that is smaller than intended.6 Newer laser technologies attempt to compensate by applying more laser energy in the periphery of the ablation, but this technique removes more corneal tissue, increasing the risk of surgically-induced keratectasia.

In a study published in 2004, dark-adapted pupil sizes of candidates for refractive surgery were found to range from 4.3 to 8.9 mm with a mean diameter of 6.5 mm.8 This finding explains why many patients had severe nighttime visual aberrations in the early days of photorefractive keratectomy when optical zones as small as 4 mm were used. In an attempt to overcome pupil size/optical zone mismatch, the standard treatment zone was increased incrementally over several years. However, even the 6.5 mm optical zone commonly used today does not prevent aberrations in many patients with large pupils, or high corrections and associated small effective optical zones.


Image degradation and visual aberrations in low light after LASIK were predictable. These problems had been widely recognized and reported with previous refractive surgeries such as radial keratotomy (RK) and photorefractive keratectomy (PRK), and were related to pupil size.9 If corneal refractive power is not consistent across the entire diameter of the pupil, visual aberrations and loss of contrast sensitivity result. After cataract surgery or refractive lens exchange, patients also report poor vision at night when the pupil dilates. As phakic intraocular lenses begin to replace LASIK for high myopia due to safety concerns, the pattern of patients with large pupils experiencing night vision disturbances is consistent.


Public Health Concerns Following LASIK Surgery
Dr. Leo Maguire forewarned of the threat to public health posed by impaired night vision following refractive surgery.10 The following is an excerpt from an editorial published in the March, 1994 edition of American Journal of Ophthalmology:

“I hope the reader will now understand how a patient may have clinically acceptable 20/20 visual acuity in the daytime and still suffer from clinically dangerous visual aberration at night if that patient’s visual system must cope with an altered refractive error, increased glare, poorer contrast discrimination, and preferentially degraded peripheral vision. People die at night in motor vehicle accidents four times as frequently as they do during the day, and these figures are adjusted for miles driven. Night driving presents a hazardous visual experience to adults without aberrations. When we discuss aberration at night we are considering a possible morbid effect of refractive surgery.”


A Brief Chronology of Scientific Literature on Night Vision Impairment after Corneal Refractive Surgery
Factors responsible for visual impairment in low light following refractive surgery have been discussed in articles and reported in peer-reviewed studies for two decades:

1987
“For a patient to have a zone of glare-free vision centered on the point of fixation, the optical zone of the cornea must be larger than the entrance pupil. The larger the optical zone, the larger the field of glare-free vision.”11

1993
“Optical zone diameters must be at least as large as the entrance pupil diameter to preclude glare at the fovea, and larger than the entrance pupil to preclude parafoveal glare.”12


1996
“At nighttime, when the pupil dilates, rays from treated and untreated areas of the cornea reach the retina at different foci and produce haloes.”13


1997
“Corneal modulation transfer function calculations suggest that a significant loss of visual performance should be anticipated following photorefractive keratectomy, the effect being the greatest for large pupil diameters.”14


1998
“…after PRK, the diameter of the entrance pupil greatly affects the amount and character of the aberrations…”15


1999
“Changes in functional vision worsen as the target contrast diminishes and the pupil size increases.”16

2000
“The increase in ocular aberrations was significantly related with the virtual pupil size.”17
“Thus, an optical system may have no refractive error in the center of the pupil and an increasing error in the annular zones surrounding the pupil center. The resultant image may be sharp for small pupil diameters but degrade as the pupil expands.”18


2002
“The relation between pupil size and the optical clear zone are most important in minimizing these disturbances in RK. In PRK and LASIK, pupil size and the ablation diameter size and location are the major factors involved.” 19

The LASIK industry failed to take corrective action in response to scientific evidence regarding the importance of matching the effective optical zone to a patient’s pupil size. As a result, many LASIK patients are now permanently visually impaired in dim light.