The Incidence and Significance of Optic Atrophy In Patients with Mental Retardation

The University of New England College of Osteopathic Medicine

Optic abnormalities are very common among mentally retarded individuals. One specific type of optic abnormality commonly seen in mentally retarded individuals is optic atrophy. Optic atrophy, is defined as: "atrophy of the optic disc resulting from degeneration of the nerve fibers of the optic nerve and optic disc" (Dorlands 28th edition). Optic atrophy can be seen during a routine optometric exam using a slit lamp. Often times, the etiology of the optic atrophy is known. Some of the common primary diagnoses in the mentally retarded that accounts for their optic atrophy are birth-related injuries (Luna et. al.1995) or developmental abnormalities, such as septo-optic dysplasia (SOD) (Willnow et. al.1996).

De Morsier was the first person to define SOD. In 1956, he defined SOD as being associated with optic nerve hypoplasia and the absence of the septum pellucidum (Rush et. al 1970). Some of the common features of SOD are optic atrophy, absent septum pellucidum, and minimal corpus callosum. Fifteen years after de Morsier first described SOD, it was discovered that pituitary failure was also a feature of the syndrome. It appears that the pituitary failure associated with SOD is actually caused by hypothalamic damage. It has been suggested that hypothalamic dysfunction and the optic atrophy of SOD may have a common underlying etiology.

In order to make a definitive diagnosis of septo-optic dysplasia, neuroimaging techniques need to be used (Brodsky et. al.1997). If SOD is diagnosed, adequacy of pituitary function should be ascertained. Arslanian and colleagues(1984), documented growth hormone deficiencies in 88% of patients he evaluated who were diagnosed with SOD. He also noticed 56% of this population had adrenocorticotropic hormone deficiencies, as well as 19% were TSH deficient. Arslanian's results further support the relationship between SOD and hypothalamic pituitary dysfunction.

The mechanism of the hypothalamic/pituitary dysfunction associated with SOD can be explained by the proximity of the optic tracts to the hypothalamus. Therefore damage to the visual system, regardless of the cause, may affect the functioning of the hypothalamic system (Willnow et. al. 1996). Willnow further demonstrated a relationship between SOD and endocrine deficiencies. His research revealed 64% of patients with SOD had hypopituitarism.

The most compelling data has been presented by Brodsky and colleagues(1997). Brodsky demonstrated that individuals who have SOD are at a greater risk for sudden death. The cause of the sudden death appears related to adrenal crisis, during viral illness. Clinically, there is fever, thermoregulatory disturbances, dehydration, and hypothalamic pituitary adrenal dysfunction. It was concluded that children with SOD and hypocortisolism are at risk of sudden death during febrile illness.

Septo-optic dysplasia is not the only disorder in which optic atrophy and hypothalamic pituitary dysfunction is seen. Oktan and colleagues(1995) demonstrated that patients with Wolfram syndrome had both optic atrophy and pituitary dysfunction. Therefore, combined optic atrophy and endocrine dysfunction are not limited to SOD.

Thus in several different syndromes, which include optic atrophy as a symptom, there often times are hypothalamic dysfunctions. The relevance of this correlation is that hypothalamic pituitary dysfunction can directly increase morbidity and mortality in mentally retarded persons (Brodsky et. a1.1997).

In the current study all patients at Hunterdon Developmental Center (a State ICF/MR facility in Clinton NJ) were evaluated for the presence optic atrophy. Our goal was to identify a sub-group of mentally retarded individuals who may have an increased risk of morbidity and mortality as a result of having optic atrophy.

Methods

All residents (n= 626) of Hunterdon Developmental Center (HDC) were given a complete optometric examination between dates: January 1 1993 and December 31, 1997. Sixty-one residents were unable to participate in the current research due to the inability to obtain an adequate optometric exam. Reasons for dismissal from the study were as follows: inability to cooperate with the examiner, absence of globes, and/or calcification, ossification, or fibrosis of the globes.

Therefore, 565 residents were included in the current research. A formal consultation report of the optometric exam was generated and used for data collection purposes. Information regarding the patient's sex, date of birth, primary diagnosis, and optometric examination results were recorded and analyzed.

Results

Five hundred sixty five (90.3%) of the residents were given a complete optometric exam, 339 (60.0%) were male and 226 (40.0%) were female.

Of the residents examined, 62 (11.0%) were found to have pale discs or optic atrophy.

Of those patients with optic atrophy, thirty-seven (59.7%) were males and 25 (40.3%) were females. Males with optic atrophy ranged in age from 19 to 65 years with a mean age of 39.3 years, and a median age of 36.0 years. Females ranged in age from 28 to 79 years with a mean age of 42.8 years, and a median age of 37 years.

The primary diagnosis of brain disorder responsible for the mental retardation(and possibly the optic atrophy as well) included: Hydrocephalus 6 (9.69%), prematurity 5 (8.06%), birth related anoxia 5 (8.06%), post natal trauma 4 (6.45%), genetic chromosomal 3 (4.83%), disorders of brain formation 3 (4.83%), tumor 3 (4.83%), central nervous system infection 2 (3.23%), and aneurysm 1 (1.61%).

However, in 30 (48.4%) of the residents with mental retardation and optic atrophy, the etiology of the brain disorder was unknown.

Discussion

The residents who participated in the current study were reflective of the population at HDC, both in gender and age range, 59.7% males and 40.3% females , and 19 -79 years, respectively. Furthermore, when the primary diagnosis of the brain disorder responsible for the mental retardation was known, it reflected common syndromes which also have optic atrophy as part of their symptoms, such as: Hydrocephalus, prematurity, birth related anoxia (Luna et al 1995), post natal trauma (Murphy et al 1997), genetic chromosomal (Votruba et al 1997), disorders of brain formation (Lizcano et al 1995), tumor, central nervous system infection (Koraszewska et al 1995), and aneurysm. Since the etiology of the mental retardation and optic atrophy was unknown in 30 (48.4%) of the residents at HDC with optic atrophy further evaluation needs to be done. A full hypothalamic pituitary work-up is necessary in these individuals, to determine if these residents are at risk for sudden death (Brodsky et. al.1997).

Furthermore, just because the etiology of optic atrophy is known in other patients it is still possible that they are at risk for hypothalamic pituitary abnormalities, due to the relationship, anatomically, of the optic nerve, optic chiasm, and optic tracts to other structures in the brain.

It is entirely possible, as a result of this close proximity; other systems may be affected by optic atrophy. These complications are the factors that may influence adequacy of response to stress and therefore affect morbidity and mortality in mentally retarded individuals. Further study needs to be done to examine and determine the adequacy of pituitary function in patients with mental retardation and optic atrophy This is because of the possibility that they may be at an increased risk for sudden death, due to infections of other causes of stress.

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