The employer and insurer appeal from the compensation judge’s finding that the employee’s medical care and treatment, in the nature of an artificial iris/intraocular lens implant, was a natural consequence of the employee’s 1991 work-related injury and from the judge’s related finding that a subsequent non-work-related incident did not constitute a superseding, intervening cause of the need for that treatment.  We affirm.

On May 22, 1991, Thomas Michlitsch [the employee] sustained an injury to his left eye while working for Michlitsch Builders, Inc. [the employer].  He was treated at Minneapolis Medical Eye Clinic and diagnosed with traumatic hyphema, traumatic cataract, traumatic iritis, and a marked angle recession of the left eye.  The employee subsequently underwent cataract surgery and placement of an intraocular lens.  An additional surgery was performed in 1993 in an attempt to address the employee’s glare symptoms, but that procedure was only partially successful.  Thereafter the employee continued to report problems with light-related visual disturbances, including photophobia and glare.

On March 7, 2005, the employee returned to Minneapolis Medical Eye Clinic with a history of changes in his vision, increased glare sensitivity, and frequent headaches.  Three weeks later, at a visit on March 28, 2005, the employee reported having experienced distorted and fuzzy vision in his left eye on awakening that morning.  During the night, he had gotten up to use the bathroom and had walked into a door, striking the left side of his head.  He was referred to Dr. Daniel Hardten, who diagnosed a dislocated implant and recommended a subtotal vitrectomy and intraocular lens exchange, for placement of an artificial iris.  In a May 4, 2005, letter to the employer’s insurer, State Fund Mutual Insurance Company, requesting approval for the surgery, Dr. Hardten stated,

The employee evidently underwent the recommended surgery on September 27, 2005.  About that same time, the employer and insurer obtained a medical record review by neuro-opthalmologist Dr. Alan Weingarden.  In a report dated October 6, 2005, Dr. Weingarden diagnosed traumatic cataract and dislocated intraocular lens secondary to the employee’s head trauma at home in March 2005.  He agreed that the surgical approach recommended by Dr. Hardten was reasonable, but he did not believe that the procedure would have been necessary absent the trauma on March 27, 2005.

The employee’s claim for payment for the artificial iris/intraocular lens implant surgery was submitted to a compensation judge for determination based on stipulated facts.  The issue presented to the judge was whether the employee’s need for surgery was a natural consequence of the work-related injury of May 22, 1991, and thus compensable, or whether it was a noncompensable result of a superseding, intervening cause.  In a Findings and Order issued January 20, 2006, the compensation judge determined that the employee’s activity of getting up in the middle of the night to go to the bathroom and walking into a door was not unreasonable, negligent, dangerous, or abnormal activity on the part of the employee.  She determined also that that activity by the employee did not constitute a superseding, intervening, independent cause of the employee’s need for surgery.  She therefore found that the employee’s need for surgery was a natural consequence of the work injury of May 22, 1991, and she ordered payment of the claimed medical expenses.  The employer and insurer appeal.

On appeal, the Workers’ Compensation Court of Appeals must determine whether “the findings of fact and order [are] clearly erroneous and unsupported by substantial evidence in view of the entire record as submitted.”  Minn. Stat. § 176.421, subd. 1 (2004).  Substantial evidence supports the findings if, in the context of the entire record, “they are supported by evidence that a reasonable mind might accept as adequate.”  Hengemuhle v. Long Prairie Jaycees, 358 N.W.2d 54, 59, 37 W.C.D. 235, 239 (Minn. 1984).  Where evidence conflicts or more than one inference may reasonably be drawn from the evidence, the findings are to be affirmed.  Id. at 60, 37 W.C.D. at 240.  Similarly, findings of fact should not be disturbed, even though the reviewing court might disagree with them, “unless they are clearly erroneous in the sense that they are manifestly contrary to the weight of the evidence or not reasonably supported by the evidence as a whole.”  Northern States Power Co. v. Lyon Food Prods., Inc., 304 Minn. 196, 201, 229 N.W.2d 521, 524 (1975).

As a general rule, an employer is liable for medical expense if the employee’s need for treatment is due in substantial part to the work injury.  The work injury need not be the sole cause of the need for treatment; it is only necessary for the employee to show that the personal injury was a legal cause of the medical expense, that is, a substantial contributing cause.  Roman v. Minneapolis Street Railway Co., 268 Minn. 367, 129 N.W.2d 550, 23 W.C.D. 573 (1974).  The employer is not, however, liable for medical expenses resulting from a superseding, intervening cause.  In Buford v. Ford Motor Co., 52 W.C.D. 723 (W.C.C.A. 1995), this court explained that “[a] superseding intervening cause is one which severs the causal link between the original personal injury and the resultant disability such that the original personal injury is no longer a substantial and contributing cause of the resultant disability.”  Id. at 728.  The determination of whether a subsequent incident or event is a superseding, intervening cause of disability is one of fact, and the employer and insurer have the burden of proof.  Turney v. Ebenezer Soc’y, 39 W.C.D. 809, 818 (W.C.C.A. 1986), summarily aff’d (Minn. Apr. 9, 1987).

In the present case, the compensation judge determined that the employee’s need for surgery was compensable as a natural consequence of his work-related injury of May 22, 1991.  In so concluding, the judge relied on a line of supreme court cases commencing with Eide v. Whirlpool Seeger Co., 260 Minn. 98, 109 N.W.2d 47, 21 W.C.D. 437 (1961).  In Eide, the court held that where a permanently weakened physical condition caused by a personal injury is aggravated by an employee’s subsequent normal physical activities to the extent of requiring additional medical treatment, such treatment is compensable, so long as it could be said that the additional care was “a natural consequence flowing from the primary injury” and not the result of “unreasonable, negligent, dangerous, or abnormal activity on the part of the employee.”  Id. at 102, 109 N.W.2d at 49-50, 21 W.C.D. at 441.  In Gerhardt v. Welch, 267 Minn. 206, 125 N.W.2d 721, 23 W.C.D. 108 (1964), the court, again reviewing the range of compensable consequences of a personal injury, adopted the “direct and natural consequence rule” set forth at 1 Larson, Workmen’s Compensation Law, § 13.00, which provided:

The employer and insurer argue that the compensation judge erred in finding causation between the employee’s injury of May 22, 1991, and his subsequent need for surgery in 2005.  They contend they are not responsible for the procedure to replace the employee’s lens implant because the need for that surgery was exclusively caused by the intervening event of March 27, 2005, which was not a natural consequence of the work-related injury.  In the absence of that trauma, they assert, the employee would not have required the surgery and treatment at issue.  Citing Wallace, the employer and insurer maintain that the “occurrence” causing the employee’s implanted lens to become dislocated was not causally related to the original injury and therefore cannot be a consequence of that injury; if mere involvement of the work-related condition was the criterion, they contend, there would be no such thing as an intervening cause.

We believe that the employer and insurer’s interpretation of Wallace is too broad.  In that case, the employee’s second injury was found to be a consequence of the employee’s intervening conduct rather than his prior work injury, where the employee, who had an immobilized knee as a result of his work accident, was standing on an old door supported by 2 x 4s about seven or eight feet off the floor, attempting to tip the roof off an old house, when the supports collapsed.  The employee fell, fracturing his leg above the knee.  The supreme court distinguished these facts from those in Eide.  In Wallace, it could be said that employee’s own conduct, given his immobilized knee, was so unreasonable, negligent or dangerous as to be considered an intervening, superseding cause of employee’s second injury.^[2]

In the present case, the judge concluded the employee’s additional medical and hospital expenses were a consequence of the original injury as aggravated by an ordinary activity.  The employer and insurer’s contention that compensability for a subsequent non-work-related injury or aggravation depends on whether the occurrence is causally related to the original injury misinterprets the court’s holding in Wallace.  If all that was necessary to break the chain of causation was to have a new “occurrence,” there would be no need to evaluate fault, negligence, or the employee’s own intentional conduct, as contemplated by Eide.  Under the employer and insurer’s theory, even injury or aggravation caused by a sneezing incident, because the incident was unrelated to the original injury, could not be considered a compensable consequence of the primary injury.  This is clearly not the law in Minnesota.  See Rohr v. Knutson Constr. Co., 305 Minn. 26, 232 NW2d 233, 28 W.C.D. 23 (1975).

We believe that this case is controlled by Eide.  As found by the judge, the triggering episode for the employee’s medical complications was not “unreasonable, negligent, dangerous, or abnormal activity on the part of the employee.”  The employee’s permanently weakened condition did not cause the subsequent incident, but the weakness clearly made the employee more vulnerable to the very injury that occurred.  As such, there remains a causal relationship between the original injury and the employee’s subsequent need for medical treatment.  The judge’s conclusion that the episode at home aggravated a permanently weakened condition and was “a natural consequence flowing from the primary injury” is supported by substantial evidence and is affirmed.  Hengemuhle v. Long Prairie Jaycees, 358 N.W.2d 54, 37 W.C.D. 235 (Minn. 1984).