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.).  Philadelphia, W. B. Saunders.  1994:1289-1684.

 

2/15/08