Clinical
Practice Guideline
for
GLAUCOMA and
OCULAR HYPERTENSION
Developed for the
Aerospace Medical Association
by their
constituent organization
American Society of Aerospace Medicine Specialists
Overview: Aeromedically, ocular hypertension (OHT) is defined
as: (1) intraocular pressure (IOP) by applanation greater than 21 mmHg but less
than 30 mmHg on two or more determinations, or (2) 4 mmHg or more difference
between the eyes performed by applanation tonometry. (Adjustment of applanation IOP either up or
down based on cornea thickness is not aeromedically approved to
establish a different applanation IOP than what was originally obtained). In addition, the eye examination should
assess for the following indicators of optic nerve damage: optic nerve cup
enlargement greater than 0.4, cup-to-disc asymmetry greater than 0.2,
progressive optic nerve cupping changes, nerve fiber layer loss, optic nerve
hemorrhage, visual field defects, color vision defects and relative afferent
pupillary defect. Glaucoma is defined as
IOP of 30 mmHg or greater by applanation, or any evidence of the secondary
changes associated with optic nerve damage as stated above. Pressure-related optic nerve damage can occur
at any level, i.e. low tension glaucoma; however, glaucoma usually occurs among
individuals with IOP spikes of 22 mmHg or greater. Statistically, the higher the pressure spike,
the greater the risk for optic nerve damage.
Historically, the term glaucoma has been used in aircrew with pressures
of 30 mmHg or greater even in the absence of objective nerve damage. Medical treatment to lower IOP is almost
always indicated in individuals with IOP measured at 30 mmHg or greater by
applanation even when no current glaucomatous damage exists. Medical treatment to lower IOP is indicated
for anyone diagnosed with “glaucoma,” including individuals diagnosed with
normal or low tension glaucoma. The term
“glaucoma suspect” or “pre-glaucoma,” is often used when enlarged optic nerve
cupping and/or ocular hypertension exists indicating close monitoring is
required. These terms both imply no
definitive glaucomatous visual field defects, nerve fiber layer defects,
acquired color vision defects, or progressive optic nerve cup enlargement
currently exists.
The etiology and differential diagnosis of OHT/glaucoma is
diverse. The glaucomas are divided into
open angle (primary, secondary, normal tension) and closed-angle types. Primary open angle glaucoma is the most
common primary glaucoma and has a strong inheritable pattern. Pigmentary glaucoma is the most common
secondary glaucoma and is caused by elevated IOP resulting from pigment
dispersion syndrome. In pigment
dispersion syndrome, pigment granules are liberated from the posterior iris surface
which may transiently block aqueous humor outflow from the anterior chamber
through the trabecular meshwork, resulting in elevated IOP. Pigment dispersion syndrome alone is not
disqualifying. However, if either ocular
hypertension or glaucomatous optic nerve damage are present along with pigment
dispersion syndrome, the condition is disqualifying. Angle closure glaucoma is uncommon in the
aircrew population because this condition typically affects individuals of more
advanced age. However, narrow angle
configuration of the anterior chamber may be diagnosed among aircrew,
especially those with higher levels of hyperopia, which may place the aircrew
member at risk for pupillary block and resultant angle closure. A thorough history and ophthalmologic exam
are essential in determining the etiology and risk for progression.
Typically, risk of glaucomatous progression increases with
age. Additional risk factors for primary
open angle glaucoma include positive family history in a first degree relative,
race (African-American), ocular hypertension, and relatively thin central
corneas as measured by ultrasound pachymetry.
In the general population, 1 of every 10 individuals will
develop glaucomatous damage within 5 years of diagnosis of OHT. Essentially, the same risk occurs in military aircrew--10%
of aircrew with ocular hypertension will develop glaucoma during the span of a
normal Air Force aviation career. Ocular
hypertension treatment decisions should be based on the constellation of risk
factors present, including central corneal thickness measurement
(pachymetry). However, the relationship
between corneal thickness, ocular hypertension and glaucomatous vision loss is
currently undefined in the age group of military aircrew population. In addition, no single standardized nomogram currently
exists to adjust for elevated IOP (adjustment factors currently being used vary
widely). Therefore, applanation IOP
adjustment based on corneal thickness is prohibited in determining whether an
individual meets aircrew standards.
Therapy for glaucoma depends upon
the specific cause. In general, the
initial management is pharmacologic.
Other therapeutic modalities include laser therapy and surgical therapy,
e.g. filtration surgery, placement of setons,
goniotomy, trabeculotomy, trabeculectomy, trabeculoplasty and cycloablative
procedures.
Aeromedical Concerns: Enlarged optic nerve cupping and OHT
may be indicators of early glaucoma.
Elevated IOP may result in difficulty with night vision secondary to the
appearance of halos and flares around lights, and decreased contrast
sensitivity. Left undiagnosed or
inadequately treated, glaucoma can cause acquired changes in color vision, loss
of central or peripheral visual fields, loss of visual acuity, and blindness. All of these visual disturbances have the
potential to impair the aviator’s visual performance and present a significant
safety hazard or adversely impact mission effectiveness. Glaucoma associated visual degradation occurs
insidiously without subjective complaints which makes the screening program
even more vital.
Medical Work-up: (This section just applies to military cases) For initial waiver request for
OHT and glaucoma, the following information is required:
1. Aeromedical summary with a thorough
review of past medical history and family history. Past ocular history should include a review
of eye injuries, surgery, previous infectious or inflammatory eye disease,
intraocular pressure history, previous visual field findings and presence or absence
of associated risk factors including family history of glaucoma.
2. Complete ophthalmologic examination
to include: refraction to best visual
acuity, Humphrey visual field testing (preferably 30-2), applanation tonometry
with diurnal measurements (at least three measurements at different times of
the day), dilated funduscopic exam. For
OHT and glaucoma, examination should also include central corneal thickness and
optic disc photographs if available.
When enlarged or asymmetric optic nerve cupping is detected
on examination, local evaluation to rule-out ocular hypertension and visual
field loss is required. Diurnal
intraocular pressure readings and Humphrey visual field testing (preferably
30-2) should be accomplished.
Physiologic optic nerve cupping and asymmetry should be monitored on an
annual basis. In cases of suspicious
optic nerve appearance or suspicious visual field abnormalities, detailed
ophthalmologic evaluation is required.
For a military waiver renewal of OHT and glaucoma, an
ophthalmology consult is required. The
evaluation should include quarterly measurements of intraocular pressure,
unless the ophthalmologist specifies less frequent assessment, and bilateral
Humphrey visual field exams.
Aeromedical Disposition
(military): Physiologic
enlargement or asymmetry of the optic nerve cup is no longer disqualifying once
ocular hypertension and glaucomatous visual field defects have been ruled
out.
OHT is a disqualifying condition for all military flying
classes. OHT is not waiverable
for any initial flying training. OHT waiver
criteria for trained aircrew include:
acceptable visual performance on ophthalmologic examination, stabilized
intraocular pressures and no evidence of optic nerve damage (as defined
above).
Glaucoma is disqualifying for all military flying classes. Glaucoma is not waiverable for any
initial flying training. Glaucoma waiver
criteria for trained aircrew include:
stable glaucoma controlled by waiverable medications or laser treatment
modalities, no aeromedically significant visual field defect within the central
30 degrees of either eye, a full binocular visual
field, and no visual or systemic medication side effects.
When pharmacological intervention is
required to control IOP, the current waiverable topical medications include
beta blockers and latanoprost (Xalatan).
The degree of beta blockade resulting from ophthalmic timolol is
proportionately much less than oral, with perhaps a 20-30% reduction in reflex
cardiovascular responses at the plasma levels achieved with such therapy. This degree of blockade is unlikely to result
in any real impairment. On the other
hand, latanoprost appears to be more effective at reducing intraocular
pressure, and has no known effect on cardiovascular homeostasis. Thus, Xalatan® appears to be the first-line
choice for high-performance aviators requiring treatment. Should the local effects of latanoprost prove
to be a problem, or should it prove necessary to add a beta blocker to control
intraocular pressure, Timoptic-XE® is associated with lower systemic levels and
improved patient compliance, and would be the preferred preparation. Furthermore, punctual occlusion during
administration of eye drops will decrease the systemic absorption of medication
and should be encouraged during the use of β-blockers. Pilocarpine and related medications are not
waiverable, neither are alpha agonists nor carbonic
anhydrase inhibitors, i.e. acetazolamide (oral) or dorzolamide
(topical).
Laser surgical procedures such as argon laser
trabeculoplasty (ALT), selective laser trabeculoplasty (SLT), peripheral
iridotomy (PI), or iridoplasty may be performed on aviators with demonstrated uncontrolled
OHT or progressive glaucoma. Waiver request
for these procedures should be submitted following successful laser treatment
once the treated eye/s have stabilized (usually at least one month), IOP is
controlled and topical post-op steroids have been discontinued.
Aeromedical Disposition (civilian): In the civilian aviator population open angle glaucoma is
acceptable in all classes of medical certification. Closed angle glaucoma is disqualifying unless
successfully treated with a procedure.
The FAA has a specific form that the treating physician must complete
along with Humphrey visual fields. This
testing is required on a yearly basis.
All of the medications are acceptable as treatment for the exception of
Pilocarpine. Stable peripheral visual field loss has been accepted. Glaucoma is one of the medical conditions
that the FAA will allow aviation medical examiners to issue after they evaluate
the airman on the initial presentation.
Waiver Experience (military): The Ophthalmology Branch at the US
Air Force Aeromedical Consultation Service has followed over 550 aviators with
the diagnosis of either OHT or glaucoma.
Aeromedical experience reveals that approximately 90% of trained
aviators are granted initial waiver for these conditions.
Waiver Experience (civilian): As of November 2007 there were 383 first-, 616 second-, and
2,095 third-class airmen who are currently issued medical certificates with
ocular hypertension and glaucoma.
References:
1. Freidman DS, et. al., Assessment of risk factors for the progression of ocular
hypertension and glaucoma.
American Journal of Ophthalmology (supplement). Sept 2004; Vol
138:S19-S31.
2. Principles and Practice of Ophthalmology. Clinical Practice. Vol 3, Albert
D., Jakobiec F. (eds.).
2/15/08